Arthropods - General

Animals: Arthropods-Hexapoda Ziser Lecture Notes, 2009 1

Arthropods - General

1,100,000 known species; at least 2-50 M more species

includes: crabs, crawfish, shrimp, spiders,scorpions, mites, ticks, millipedes, centipedes,insects (dragonflies, butterflies, ants, wasps,beetles, etc)

“jointed legs”

more species in this phylum than in ANY phylum of ANY kingdom of life

includes 2/3rds of all known animals

possibly 50 Million not yet described

one of the most ancient phyla

one of the few that existed before the Cambrian explosion

rich fossil record

many unusual forms now long extinct

very active and energetic animals

very adaptable body plan


easily modified for a wide variety of lifestyles

more widely distributed over the earth than any otheranimal phylum

live in virtually every habitat on earth

in terms of numbers of individuals:

200 M individual arthropods for everyperson on earth

most <6 mm long

largest: Japanese crab 19’ (5.79 M), 40lbs (18kg)smallest: mite <0.1 mm

tremendous economic importance to humansfoodpollinationdrugs, dyes, silk, honey, waxcrop pestsvectors of disease

were the first animals to move onto land

Silurian 420 MY ago

were the 1st animals to fly

150 MY before flying reptiles, birds, bats

insects 330 MY; Carboniferous


pterosaurs 170 MY;late Jurassicbirds 150 MY; (coexisted with pterosaurs

for ~90 MY)bats ~40 MY; late Eocene

opened up a whole new set of ecosystems andhabitats

before anything else began to compete for thesame resources

allowed wide and rapid distribution anddissemination across the globe

Body Plan

well developed head (cephalization)

with numerous sense organs

antennae & compound eyes are characteristicsense organs of arthropods

brain (ganglia)

several pairs of feeding appendages

segmented body

allows infinite possibilities for adaptivemodifications


lots of fusion of segments into a variety of body plans:

cephalothorax & abdomen

head & trunk

head - throax - abdomen

paired jointed appendages

also highly adaptable: walking, swimming,feeding, flying, breathing, reproduction, senses

Body Wall

body is completely covered with hard exoskeleton

also folds into mouth and anus to form lining of foregut and hindgut

cuticle also lines tracheae

excellent for protection

also waterproof good for life on land

main component is chitin (a starch) but much thickerthan the chitin of previous animal phyla

chitin is further hardened with proteins and calciumdeposits


exoskeleton is secreted by epidermis

often highly colored:camoflagerecognitionwarning

exoskeleton consists of many separate hardened plates

with flexible hinges between

areas where cuticle hasn’t been hardened

muscles are attached to fingerlike inner extensionsof skeleton (=apodemes)

when muscle pulls it moves part

eg. lobster closes claws

the exoskeleton also contains various folds, flaps andspines:

parts modified for feeding

structures for respiration, swimming & mating

some act as sensory organs

with the advantages of this exoskeleton it has one


major drawback:

animals can’t grow without shedding and regrowing a larger exoskeleton

Molting

problem is solved by molting

a complex process requiring environmental factors and the interaction of various hormones

eg. insects go through a fixed # of molts tilladulthood, then they don’t molt anymore

eg. spiders molt indefinite # of times throughouttheir lives

a. molting is usually initiated by environmentalcues or a buildup of pressure in the body

causes the release of molting hormone (=ecdysone)

b. old cuticle softens and separates from body

c. animal extricates itself from old cuticle

animal is especially vulnerable at this point

eg. soft shell crab

must also shed lining of intestine and tracheaeat same time


d. animal inflates itself and allows new cuticle to harden

still, the advantages must have greatly outweighed the disadvantages of an exoskeleton

Movement

virtually every form of animal movement is found in arthropods: walking, running, crawling, burrowing, swimming, flying, etc

arthropods have a very complex muscular system

the jointed plates of the body and legs provide attachment point for muscles

similar to muscle bundles that move ourbones

insects have more muscles than most animalsincluding us

eg. humans have ~700 individual muscles; some insectshave 900 or more muscle organs; some caterpillars

have 4,000

Feeding & Digestion

virtually every mode of feeding: carnivores, herbivores, omnivores, parasites


head appendages modified into a variety ofmouthparts

two main varieties:

chelicerae pinchers or fangs

mandibles jawlike

with numerous accessory feeding appendages

well developed complete digestive tract:

mouth - esophagus - stomach - intestine - anus

with specialized areas for grinding and storing food

accessory glands that secrete enzymes and digestive juices

efficient areas for absorption of nutrients

Respiration

need some kind of respiratory system since waxy cuticle is impermeable to air

arthropods use a variety of respiratory systems

gillsbook gillslungs


book lungstracheae

Circulation

simple open circulatory system

coelom becomes haemocoel

has beating heart

Nervous System

similar to annelids:

dorsal brain and double nerve cord with pairedganglia in each segment

Excretion

efficient excretory system

prevents excessive water loss on land

Reproduction and Development

mostly dioecious

lots of variation in developmental stages

often quite complex


eg. larva metamorphosis adult

larvae = caterpillars, grubs, maggots

eg. nymph juvenile adult

eg. some aquatic forms with free swimming larval stage

= nauplius

often with complete change in feeding andlifestyles

eg. aquatic larva vs terrestrial adult


Classification

Major Subphyla:

1. Trilobites

4,000 species

all extinctmostly marine

2. Myriopods (centipedes & millipedes)

14,000 species

“many feet”centipedes and millipedesmostly terrestrialdistinct head with mandibles & 1 pr antennaemany similar segments

3. Chelicerates (spiders & scorpions)

74,000 species

spiders, crabs, ticks, mites, scorpionsancient groupmostly terrestrialchelicerae and pedipalps for feedingno antennaecephalothorax

4. Crustacea (shrimps and crabs)

67,000 species

shrimp, crab, barnacles, crayfishmostly marinea few freshwater and terrestrial forms


mandibles, 2 prs antennaemany appendages & many different kinds of appendagescephalothorax

5. Insects

1,100,000 species

most successful animal group87% of all arthropods62% of all animals50% of all life on earth

mostly terrestriala few freshwater, hardly any marinedistinct head with mandibles & 1 pr antennaebody consist of head, thorax and abdomen3 prs of legs, most with 2 prs of wings


Trilobites

completely extinct group; 4,000 fossil species

earliest arthropod group

appeared before the cambrian explosion

flourished during Cambrian and declined by ordovicianbecame extinct at tend of Permian

lasted 300 MY

marine bottom dwellers (benthos)

some could burrow into the sediment

could roll up like pill bugs for protection

dominated marine benthos for 200 Million years

named for the division of the body into 3 longitudinallobes

most 2-7 cm; largest 70 cm (~2.5’)

distinct head with antennae and compound eyes

heads of many were armed with long sharp spines

not sure of any specialized mouthparts


thorax of 2-29 segments

segments added as animal grew

each segment had pair of branching appendages

one portion a walking leg

the other probably a gill

base segment of each leg had bristles or teeth

probably used to grind food and move food toward mouth

posterior end of several fused segments


Myriopods(centipedes & millipedes)

myriopods = many feet

mainly centipedes and millipedes

mostly terrestrial, many freshwater, very few marinespecies

body plan: head & long segmented trunk

1 pair of antennae

mandibles for feeding

appendages on each segment


Myriopods: eg Centipedes

“100 feet”

3000 species

some tropical species grow to 25 cm (10”) long

usually found in cool, moist habitatsunder longs and rocks

on each of the body segments is one pair ofwalking legs

from 15 to 191 pairs

but none have 50 pairs (its always an odd #)

Feeding and Digestion

most are very active nocturnal predators

mainly use antennae to detect prey;

eyes not well developed

smaller ones eat worms and insects

larger ones, such as Scolopendra of Texas, can eat lizards and small mice

mandibles are primary feeding appendages


1st pair of trunk appendages is a pair of poison fangs tosubdue prey

apparently not harmful to humans

sting causes slight paindisappears in a few hours


Myriopods: eg. Millipedes

>10,000 species

“1000 feet”

usually in moist dark places

under logs and stones

can burrow through rotting logs

body usually round in cross section

but locally, flattened millipedes are more common

millipedes are “double footed” 2 prs legs/segment

none have 1000 feet

most have fewer than 50 legs (25 prs)

maximum 752 legs (376 prs)

=Illacme plenipes; endemic to small area in California; thoughtextinct until rediscovered in 2006

some can curl up like pill bugs for defense

Feeding & Digestion

most are scavengers:


feed mainly on decaying vegetation

a few are herbivores

feed on living plants

much less active than centipedes

eyes not well developed essentially blind

mainly use antennae as primary sense organ

some are able to spray defensive chemicals from“stink” glands along sides of body for protection

eg. toxins, irritants, HCN, prussic acid

eg. a European species secretes a tranquilizer similar toquaaludes

predator (eg spider) eating itbecomes totally relaxed for several days


Chelicerates(spiders & scorpions)

an ancient group with good fossil record

include horse shoe crabs, sea spiders, scorpions,spiders, ticks, mites, sea scorpions

most are fairly small; some fossil sea scorpions(eurypterids) were 5-6’long; a few up to 9’

most members of the group are terrestrial

1s t group of animals to successfully make transition to land

oldest known fossils of terrestrial animals arechelicerate arthropods from 420 M years ago (Silurian)

Distinctive Characteristics of Chelicerates:

1. named after their main feeding appendage

chelicerae (pincer-like or fang like)used to grab or pierce or tear prey

2. most also have second feeding appendage= pedipalp

3. only arthropod group without antennae

4. most have 4 pairs of walking legs

5. head is fused to thorax = cephalothorax


Chelicerates: eg Water Scorpions

extinct group

lived from Cambrian to the Permian (especially Silurian & Devonian)

largest of all fossil arthropods

some up to 6’ long

body plan is a blend between horseshoe crabs andscorpions

cephalothorax with simple and compoundeyes, chelicerae & pedipalps

4 pr of walking legs

last pair of appendages paddlelike for swimming

segmented abdomen

spikelike telson

sluggish bottom dwellers

marine, brackish and probably freshwaters

feeding:

probably ate mostly trilobites


they were the killing machines of the oceans

one paleontologist: “ I’d much rather be in a pool with a6’ shark than a 6’ eurypterid”

Eurypterids may have been the first animals to moveonto land


Chelicerates: eg. Horseshoe Crabs

also an ancient group; but still survives today

almost unchanged for 300 million years

can grow up to 2 feet in total length and weigh up to10 lbs

Body Form

large cephalothorax, abdomen & telson

cephalothorax with compound and simple eyes

largest chelicerae of the group

pedipalps resemble the 4 pr of walking legs

all but the last pair of walking legs have “pinchers”

the last pair have small paddle-like processes for swimming

Feeding & Digestion

eats clams, snails and sandworms

mouth is in center of legs chews food with bases of legs = gnathobases

have stiff spines


uses chelicerae to help get and break up food

Respiration

breaths by flat, leaflike book gills on underside ofabdomen

they are also used for swimming

Reproduction & Development

spawn in early summer

arrive by millions on Atlantic beaches

female burrows into sand to lay eggson beach

males deposit sperm on the eggs then femalecovers them with sand

eggs hatch into larvae = trilobite larva

Ecological and Human Impacts

eggs are a valuable food source for migrating shorebirds

overharvesting of horseshoe crabs hascorrelated with a decline in shorebird numbers


are the most important food source for loggerheadturtles

used by humans as cheap fertilizer for past 100 yrs

pharmaceuticals are also extracted from them

millions are taken to be used as bait


Chelicerates: eg. Scorpions

~1400 living species

mainly in tropics and subtropics

especially deserts

secretive

active at night = nocturnal

usually stay in underground burrows in day

Texas has 18 species of scorpionsAustin has 2 species

Body Form

cephalothorax short, abdomen much longer

cephalothorax

contains large median eyes

2-5 pairs of smaller lateral eyes

no antennae

small chelicerae and very large pedipalps


4 pair of walking legs

abdomen

subdivided into a wider part and a thinner tail-like section

at tip of abdomen is stinger

Feeding & Digestion

come out at night to prey on spiders and insects

detect prey by sensing vibrations in sand with hairs onlegs and possibly pectines

large prey are subdued by injecting paralyzing venomfrom stinger at tip of tail

rarely sting humans only if provoked

venom is a neurotoxin that causes paralysis

very painful but rarely fatal

in children the more poisonous species may causeconvulsionsvomitingeven death

a few are deadly to humans


~25 of the 1500 species (2%)

none in Texas

eg. Centruroides

found in Mexico

kills 100’s – 1000’s/yr in Mexico

effect of poison is very rapidimmediate drowsinessexcessive salivationsluggish tonguesevere contractions of jaw musclesfever to 104 or 105may be hemorrhaging in stomach, lungs and

intestineswaves of convulsionscardiac irregularitiesbreathing difficulties

death usually occurs in <3hrs

if patient lives this long will probablysurvive

Reproduction & Development

scorpions have an elaborate courtship ritual and showparental care like spiders

male and femalehold each other by pinchers (chelae)touch cheliceraeand dance back and forth


male then stings female to subdue her aggression

does not permanently harm her

male deposits spermatophore on ground(a solid packet of sperm)

male maneuvers female until her genital pore is overthe spermatophore

she flips open lid of spermatophore releasing sperm into her genital opening

in some species male then flees; in others he remains to be cannibalized

provides food to nurture young

development can take up to a year

scorpions bear live young

embryos develop inside mom

development may take several months to a year

absorb nutrients from mom

at birth 1-100 babies are are born

after birth, babies climb onto mom’s back

she carries them around for a week or sobefore they set out on their own


Chelicerates: eg. Spiders

large group; 40,000 species

Body Form

two part body

cephalothorax and unsegmented abdomen

separated by small pedicel

cephalothorax

simple eyes can detect movement

in some eye may actually form image

some very good vision

eg. jumping spider, Portia, has eyes with spatial acuitybetter than most mammals and birds (better thana cat or pigeon)

most have chelicerae modified into a“switch-blade” like fang

extends and injects venom from poisongland into prey

then retracts like pocket knife


pedipalps help in manipulating food

also sensory

and to transfer sperm to female

4 pair of walking legs

with sensory setae

tactile; cover legs and detect vibrationsin web and in air

abdomen

with spinnerets for webmaking

Feeding and Digestion

all are predators

fang-like chelicerae inject venom into prey

venom can be:

1. neurotoxin

affects nervous system and musclesto cause paralysis or death

2. digestive enzymes


digest proteins to kill and liquify prey

after biting prey, spider backs off while toxin kills orparalyzes it

many spiders wrap prey with silk to further immobilize it

after prey has been subdued spider liquifies prey with digestive enzymes

eg. one African spider can liquefy a 2” fish or smallsnake in <3 hrs

spider then uses pharynx and “pumping stomach” tosuck up liquefied prey

spiders have very low metabolism:most can live for long periods without eating

eg. tarantulas several monthseg. Black Widow 200 days

Spider Webs

virtually every aspect of spider biology depends on itsability to produce silk:

used to wrap prey

silk is also used in web as “trip lines”

males produce sperm webs


females weave coccoons and build nursery webs

juveniles use it to “balloon” to new habitats

spiders have six different kinds of silk glands

each produces a different kind of silk:

sperm webdrag linecoccoonvarious parts of web

silk is made of liquid proteins (keratins) that hardenas it is secreted from glands

silk is extruded from spinnerets

tension of pulling out silk changes its structurefrom a liquid to a solid string

silk is stronger than steel of same diameter

after use it is eaten and amino acids are recycled intonew silk

3 basic types of webs:

1. sheet web

most commonleads to funnel shaped retreat in which spider awaits preyconspicuous on lawns after heavy dew


2. cobwebs

loosely wovendepend on sticky threads to snare prey

3. orb web

most intricate geometrymost well knowngeneral pattern varies by speciesspider plucks web to determine where prey is

located in web

some other variations of web and silk use:

eg. Bola Spidersproduce single sticky strandthey throw at flying insects (eg moths) to

catch them

eg. many spiders live in webs of other spiderseat host’s prey or host

Reproduction

when ready to reproduce male stops feeding

constructs “sperm web”

deposits drop of semen on it

picks up and stores semen in tip of pedipalp

goes in search of a mate

female is detected by pheromones


copulation is usually preceded by elaborate courtshiprituals

to ensure the female doesn’t treat suitor asprey

if successful, male inserts pedipalp with sperm intofemale genital opening

after mating male goes out in search of anotherfemale

female remains in web and deposits 100’s or 1000’s ofeggs in egg web

often lots of maternal care

Examples of Spiders

the two most dangerous spiders in US areBlack Widow andBrown Recluse.

both are common in Texas

both have a tendency to live in homes, outhouses and outbuildings

eg. Black Widow


has been found in all 50 states; common in centralTexas

female is the most venomous

venom is a neurotoxin

venom is 15x’s more toxic than that of aprairie rattlesnake

but so little that only ~1% of bites are fatal

native Americans of California rubbed arrows withmashed spiders for more effective hunting

causes synapses to release Ach causing:muscular spasmsabdominal rigiditycrampssweatingsalivationhigh blood pressuresometimes convulsions

eg. . Brown Recluse

So Central US include Texas

venom contains digestive enzymes

its venom contains enzymes that destroyblood cells


this induces WBC’s to attack surroundingtissues

creates large crater-like wounds that mayrequire months to heal

its bite can be fatal to children

eg. Phoneurtria sp. (Brazilian wandering spider)

also called banana spiders but NOT the same as the relatively harmless Nephila, also called banana spiders

most dangerous of all spiders

most toxic venom

Costa Rica and throughout South America east of theAndes

large spiders: 10-12 cm (4-5”) leg span

very aggressive

will attack anything (including humans) who appear aggressive

wander the jungle floor at night

in day they hide inside termite mounds, under logs and rocks or in banana plants and bromeliads


species responsible for most spider bite deaths

in some bites very little venom is released;in others a large amount is injected

bite can cause:

intense pain

sweating

acute allergic reaction

uncomfortable penile enlargement - can lead to impotence(being studied as erectile dysfunction meds)

death (esp in children injected with large dose)

eg. Camel spiders (=wind scorpions)

mideastern species

have reputation as one of the nastiest arachnids but arerelatively harmless

its said they are bigger than a human hand, extremelyaggressive, will climb onto the belly of a camel andeat the camel alive

truth: they are as large as a 5 yr old child’s hand, they can runup to 10 mph (still fastest known nonflying arthropod) and don’t eat camels or people


Human Impacts of Chelicerates:

most arachnids, though feared, are actually harmlessto humans

1. spiders are directly beneficial as predators each kill 1000’s of insect crop pests

2. large infestations of some mites can damage foodand ornamental plants by sucking their juices

2. Venomous species a few are deadly

eg. black widow

eg. brown recluse

eg. scorpions, esp Centruoides

3. Arachnid Diseases and Parasites: mites & ticks

Future Applications

scientists are experimenting with venom genes touse as biological control against insect pests

venom gene in virus infect & kill insect pest


Crustaceans(shrimps & crabs)

=shelled creatures; “the insects of the sea”

~67,000 species

eg: lobsters, crayfish, shrimp, crabs, water fleas,copepods, barnacles, pill bugs, etc

crustaceans are mostly aquatic, mostly marine

inhabit most waters of the earth: ocean , arctic , freshwaters, high mountain creeks and lakes thermal springs, brine waters

many are at the base of aquatic food chainspart of zooplankton

only a few are terrestrial; sow bugs, pill bugs

vary in size from microscopic to 12’

largest is giant Japanese crab up to 12’ from end of claws to tail

some quite colorful: blue, red, orange, yellow, mottled

many crustaceans are bioluminescent

most are free living


some are commensal

eg. sponges, corals, sea anemones

many are parasites

infect almost all classes of animals

some are sessile (=attached)

eg. barnacles

Distinctive Characteristics of Crustacea:

1. body is divided into a cephalothorax, abdomenand tail

2. only arthropods with 2 pairs of antennae

3. use jaw-like mandibles as main feedingstructures; also maxillae and maxillipeds

4. generally have many pairs of appendages modified for a variety of uses

most are branched

lots of variation between groups

Body Form

in most, body is divided into a cephalothorax, abdomen and tail


often have carapace extending over abdomenand gills

in some groups carapace forms clamshell like valves that encloses body

in some crustaceans the exoskeleton isparticularly thick and reinforced by calciumcarbonate deposits

eg. crab claws

abdomen usually with pairs of jointed appendages onmost segments

generally have many pairs of appendages modifiedfor a variety of uses:

sensoryfeedingdefensewalkingswimmingreproductionrespiration

lots of variation between groups

eg in decapods (crayfish, crabs, lobsters, etc):

1st 2 pair antennae with chemoreceptorsnext 5 pr (3-8) feeding appendages; including

mandible, maxilla and maxillipedsnext 5 (9-13) walking legs including cheliped and

gillsnext 5 (14-18) called swimmerets; used to carry

eggs and as copulatory organ


last (19) uropod = swim fin

most crustaceans can cast of legs or pinchers andregrow them

Feeding & Digestion

great variation in feeding types:

many are predators

some with appendages that cock and fire to produce pressure waves that stun prey

eg. mantis shrimp

some are suspension feeders

eg. barnacles sit upside down in shell and uselegs to strain water for food

some are scavengers

use jaw-like mandibles as main feedingstructures

well developed digestive system:cardiac stomach with gastric mill for grinding

gastric mill has hardened “teeth”


pyloric stomach for sorting

digestive gland

Respiration

no special organs in small crustacea

exchange across body surface

in larger crustacea respiration usually by gills

on bases of walking legs

in some sides of carapace form gill chambersthat enclose gills

have an appendage called a “bailer” thatcreates a water current across gills

Sense Organs

sense organs are well developed

most have compound eyes and simple eyes

chemoreceptors (taste) on mouthparts and on the s2pairs of antennae, and on other areas

statocysts for orientation, at base of antennae

saclike; opens to surface by pore


take in sand grains which trigger hair cells to provide info on orientation

tactile hairs and spines spread over body

Reproduction

most are separate sexed (dioecious)

but barnacles are monoecious

copulation: male delivers sperm packet toreceptacle using swimmeret

some develop large brood sacs for carrying eggs

many marine species have characteristic larval form


Examples of Crustacea

shrimps, crabs & crayfish

best studied groups

mainly benthic: in and on the sediment

lots of specialized legs

crabs use large claw used to break open shells to feed

fiddler crab uses largest claw for social interactions

only uses small claw for scavenging food from sand

others are filter feeders, herbivores or scavengers

cleaner shrimp remove skin parasites from fish

land crabs burrow above tide line into the water table

can survive days out of water

mantis shrimp is an ambush predator

front end looks like praying mantis

most crab and shrimp carry eggs or brood their young

planktonic crustaceans

small

a large part of the zooplankton in both marine and freshwaters are crustaceans

marine: esp. copepods & krill


krill can occur in enormous swarms and are a major part of the diet of baleen whales and many fish

freshwaters: esp. water fleas, copepods, seed shrimp

fairy shrimp & brine shrimp

barnacles

often confused with molluscs and originally classified with them

sessile: secrete shell of several calcium plates in which they live

extend feather-like legs to filter feed in the surf

almost all are hermaphrodites yet they cross fertilize with internal fertilization

eggs hatch into motile, nauplius larvae

adults secrete chemicals that attract the larvae to settle near them to facilitate reproduction

preyed on especially by starfish and snails

pill bugs & sow bugs (isopods)

only truly terrestrial crustaceans

have very delicate gill-like respiratory organs that must be kept moist

found in damp places under stones and logs

able to roll up for protection (=rolly pollys)


young develop in brood pouch

some salt water relatives are found along coasts and live in seaweed, along rocks and algae

some bore into wood causing destruction of pilings and warves

beach fleas(amphipods)

found in both freshwaters and marine habitats

some are almost terrestrial; found crawling around on piers and jettys


Economic Importance of Crustaceans

many are at the base of aquatic food chainspart of zooplankton

1. as food

eg. crab, lobster, crayfish, shrimp

some crab are harvested by breaking off claws andthrowing rest back

2. many crustaceans are serious pests

a. cause crop destruction

eg. rice crabs in China and India eat rice;burrows may drain rice fields destroying crops

eg. crayfish destroy young cotton plants

b. boring & fouling organisms

borers destroy warves & docks and woodenhulled boats

undermine sea walls and bore into stone

destroy underwater cables

adhere to ships reduce efficiency and increasehull decay


eg. barnacles

3. some act as intermediate hosts for human parasites

eg. Guinea wormlarva is in copepods; swallowed in contaminated watergrow in lymphatic systemup to 3’ longfemale produces blister like lesions on lower extremeties to

lay eggs in water

eg. fish tapewormlarva in Cyclops and Diaptomuseaten by fishhumans eat uncooked fish


Insects

1.1 M species; may be as many as 50 M

there are more species of insects than all other animalspecies

entire field of study = Entomology

most successful & widespread group of all animals

adapted to land before most other terrestrial animalsexcept a few Chelicerates

(Devonian 390 MY)

adaptations to land (even deserts):waxy cuticlevarnish layer can close spiraclesextract & retain fluids from food and metabolism

(some don’t need any liquid water at all)diapause & resistant eggs

had 40 MY to evolve and diversify before seriouscompetition for space and resources from other animal phyla

by carboniferous (~300MY ago ) there many differentkinds of insects

still no birds around yet

still not a lot of parasites of insects yet


eg. roaches were the main insects of the time

eg. some dragonflies had 2’ wingspans

today insects have spread into all major habitats

dominant fauna of all freshwater and soil habitats

some live in deep underground caves

on top of world’s highest mountains

some insects live in unusual habitats:

some flies occur by the millions in brine lakes eg. Great Salt Lake, where hardly any other life forms are able to survive

some insects live in hot springs up to 120º F (49º C)

many species are found inside ice in anarctica

larvae of petroleum flies live in pools of petroleum around oilwells

a few insects have been found breeding in brine vats holdinghuman cadavers at medical schools

the “short-circuit beetle bores into lead cables

butonly a very few are truly marine; Why?

most are <2.5 cm

small size helps them escape enemies

need very little food to sustain themselves


range from < 1 mm to 25 cm

eg. Atlas moth of India has a wingspan of almost 1 foot

eg. Walkingstick of India is up to 15” long

insects invented agriculture & animal husbandry

many ants and termites cultivate fungi within their burrows

some ants guard aphids that let the ants “milk”them for nectar-like secretion

may have invented slavery

there are ~35 species of “slave making ants” that regularlyraid the nests of other ant species and take young back totheir own colony

there they work as they would in their home colonysearching for food, raising young, etc

always very closely related species

ants will always do the work of whatever colony they are inwhen they emerge as adults

were the first animals to fly

130 MY before pterosaurs

insects: 330 MY(SN04); carboniferousreptiles: 200 MY pterosaurs; late jurassic ,birds: 150 MY; coexisted with pterosaurs for~90MYbats: 54 MY (Eocene)

Distinctive characteristics of Hexapods


1. body divided into head - thorax - abdomen

2. 1 pair of antennae

3. mandibles for feeding

4. three pairs of walking legs

5. usually 2 pairs of wings

Body Form

body in three parts: head, thorax and abdomen

Head

large compound eyes

several (usually 3) simple eyes (=ocelli)

1 pair of antennae

many kinds of antennae

eg. grasshoppers, crickets and cockroaches have longantennae

eg. butterflies have knob on end

eg. moths antennae are featherlike


antennae are very complex sense organs in which different segments control different aspects of an insects life:

eg. in ants:one segment detects nest odor and helps prevent

an ant from entering the wrong colony

another segment identifies offspring of a specific queen

another segment detects the ants own feeding trail

another segment helps detect what is needed by the immature ants it is tending

etc

mandibles and other mouthparts for feeding

Thorax

divided into three segments

each thoracic segment bears 1 pair of legs

total 6 legs; thus hexapods

most insects also have 2 pairs of wings on thorax

wings are extensions of cuticle formed byepidermis

Abdomen


segmented (10-11 segments)

reproductive organs

females have pincher like or syringe likeovipositor to lay eggs

Insect Movement

most kinds of movement are created by muscular system (striated muscles like us)

insects have a more elaborate muscular system thanany other invertebrate group

insects have more muscles than most animalsincluding us

eg. humans have ~700 individual muscles; some insectshave 900 or more muscle organs; some caterpillars

have 4,000

insects are remarkably strong, given their small size

eg. a bee can pick up 50 times its weight equivalent to human carrying 4 tons

eg. beetles are the strongest insects equivalent to us carrying 5 tons

[but their small size relative to weight makes them appear strong if insects were as large as humans they would be little ifany stronger than us]

A. Legs


great diversity of leg types:

insect legs are adapted for the same kinds ofmovements as vertebrates:

walking, running, jumping, swimming,digging, climbing, grasping

sometimes modified for

jumping (grasshoppers, crickets, fleas)

eg. grasshoppers can j ump 20 times length ofbody

equivalent jump for human would be1/3rd length of football field

eg. fleas are probably the best jumperscan jump 8 “ high and 13 inches in length

equivalent feat in human leap tall bldg in a single bound

storage of pollen (bees)

swimming (diving beetles, many insect larvae)

B. Wings

most insects have two pairs of wings

some use both pairs to fly (eg. butterflies)

some the 1s t pair cover and protect second pair(eg. beetles)


a few have only 1 pair (flies, mosquitoes)

a few are wingless (lice, fleas)

Insect Flight

insects were the first animals to fly 130 MY before any other animal

the rate of wing beating varies considerably:

fastesteg. midge >1000bpseg. housefly beat ~200bpseg. mosquito ~300bpseg. honey bee ~ 190bps

more typical beat:eg. locust ~20bpseg. dragonfly ~25bps

slowly beating:eg. white butterfly ~12bpseg. swallowtail ~5bps

speed of insect flight varies greatly:

from slowest insect flight speeds:eg. mosquitoes ~2mpheg. houseflies ~5 mpheg. butterflies ~6mpheg. honey bee ~7 mph

to quite fasteg. hawkmoth ~35mpheg. horse fly ~30mpheg. dragonflies 25 mph

flight greatly improved dispersal ability


some insects are able to migrate 1000’s of miles or fly at high altitudes:

eg. monarch butterfly flies slowly ( 6 mph)but can fly 100’s of miles at a time

eg. painted lady migrates 4000 miles

eg. some butterflies have been seen at 20,000’

some wings are only temporary structures

eg. males and queen ants use wings only for mating flight, then they drop off

Feeding & Nutrition

insects feed upon almost every kind of organic substance

all insects share the same basic mouthparts:mandibles jawshypopharynx tonguelabrum, labium lipsmaxillae

the same basic mouthparts are modified in manyways to facilitate feeding types:

a. most feed on plant juices and tissues

eg many caterpillars feed on specific plants

eg. in butterflies the maxillae form a long coiled food tubefor sucking nectar


b. many feed on dead or decaying organic matter

eg. beetles and insect larvae are

eg. in houseflies the labium forms a sponge-like feedingstructure

c. some are predaceous

d. some are parasitic

the digestive tract is a tube divided into 3 major regions:

foregut crop, salivary glands, stomachinitial food processing & temporary storage

midgut usually has sac-like gastric caecae enzyme secretion and absorption of nutrients

hindgut intestine and rectumrectum for water and nutrient absorption;

Respiration

an insects blood does not carry much oxygen

oxygen is delivered directly to body cellsthrough system of tubes and passageways

tracheal system with spiracles adaptation to air

many spiracles have valves


lined with cuticle must be shed

gas movement by diffusion

larger insects use some kind of ventilationeg. pumping movement of abdomen

Sense Organs, communication & behavior

most insect sense organs are microscopic in size andare found on the body wall and variousappendages:

1. Touch

small hairs on body generally respond to touch

most touching involves antennae and mouthparts

these touch receptors can also pick up vibrations inair to respond to wind or gentle breeze

eg. a fly avoids a swat by ‘feeling’ the air being pushed byyour hand as you try to swat it

can also detect temperature, humidity, gravity

touch receptors are used to:

a. recognize nest mates

eg. mole cricket uses antennae to recognize nymphs indark burrow


eg. social insects can detect unwelcomed visitor totheir nest and attack them

b. social insects often stroke and groom eachother with antennae and mouthparts

c. waggle dance of honeybees involvestouching to communicate location of pollen

2. Vision

two kinds of photoreceptors in insects:ocelli usually 2 or 3 on head

can detect only light vs dark

compound eyes

with many individual lenses = facets

provide a wide field of view andparticularly good at detectingmovement

3. Hearing & Sound

insects have many different kinds of organs forhearing

many insects have hearing organs inside theirlegs that respond to vibrations passingthrough the ground or a plant


eg. ants come out of nest if you stomp on theground

cicadas and crickets detect sound with anear-like tympanum

sound may be used to attract individuals of thesame species

eg. males and female mosquitoes are attracted to eachother by sound of their buzzing wings

eg. tapping sound of death watch beetles (eat woodon old house -heard by those keeping watch overdead person before burial) used to attract a mate

many insects that can hear have structures formaking various sounds to communicate witheach other or to other species

some rub body parts together to make sounds= stridulation

eg. chirping sound of crickets, katydids, beetlesand ants

some have drum like membrane that canvibrate to make a sound

eg. cicadas are loudest of all insects can be heard half mile away songs differ for each species

hissing cockroach blows air out its spiracles tomake sound


4. Taste, Smell & Chemical Communication

chemoreceptors are found on all parts of the insects body

on setae, antennae, mouthparts, legs

but are mainly on antennae and feet

wasps and crickets know where to lay eggsbecause they have chemoreceptors on their ovipositors

most insects have the same 4 taste sensations asdo humans: sweet, sour, bitter and salty

organs of smell do not detect as many differentodors as does a human nose

but it is tuned more finely

can detect differences between verysimilar chemicals and in much lesseramounts

eg. male of lesser emperor moth can smell thepheromone of the female up to 6 miles away

some can detect airborne chemicals 5 milesaway

used to find suitable plant for laying eggsflies to find dead animalssome parasitic wasps can track host species

chemical pheromones are used to communicate


within a species, respectively

eg. sex pheromones attract mates

eg pheromones that cause grouping behavior

eg. ants release alarm pheromones if disturbed orthreatened

eg. ants, caterpillars and other insects produce trailpheromones to map route to food

allomones are chemicals produced by one speciesthat affect another species; defensivechemicals

eg. stink bugs produce defensive allommones to wardoff other species

some of these chemicals can be painful andcause temporary blindness

eg. Bombadier beetle

in addition to external senses insects also have avariety of proprioceptors

can monitor body positions, eg legs and wings,internal pressures

could not walk or fly without this info

Behavior & Communication

insects have keenly developed senses


can be used for communicationand behavioral responses

insect behavior is mostly instinctive (innate)

eg. caterpillar is programmed to eat a certain plant

but they do have the ability to learn

eg. bee dance

eg. notice landmarks near nest or food

eg. when Colorado potato beetles first attempt to mate,they are not very good at identifying their own species

or even distinguishing head from tail; with repeatedattempts they get better at it

colonial insects (eg. ants, bees) can work muchmore efficiently as a group than any solitary insect

have very structured division of labor

eg. in relative size, ants have one of the largestbrains among insects (equivalent to the processing power of an Apple II computer)

an ants brain contains ~ 250,000 cells a colony of 40,000 has collectively as many cells as a

human brain

Reproduction & Life Cycles

wide range in life spans for adult insects:hours to years


eg. adult mayflies live for less than a day; do not eat

sole purpose is to reproduce

eg. species with longest lifespan may be a tropical termite whose queen may live for 50 years

most insects also go through several distinctdevelopmental stages as they grow from egg to adult

insects are dioecious

most have internal fertilization

to find mates

most use pheromones

some use light; eg. lightning bugs

others use sound or color

often have courtship rituals

internal fertilization

male inserts sperm into females seminal receptacles

many females mate only once/lifetime and store the sperm

usually lay many eggs

eg. queen honeybee >1 M/lifetime

eg. termites lay 10,000 or more/day


eg. cockroaches can lay >1 million eggs in a year

but some only 1 egg per mating

some lay eggs on specific plant or animal

many insects “mark” plant with chemical todissuade other females from depositing eggsthere

ID of the chemical they use may beuseful as a natural insect deterrent

some may care for young after hatching

development

insects often have complex development includingmetamorphosis

a. 88% have complete metamorphosis(holometabolous):

egglarvapupa adult

larva usually has chewing mouthparts

pupa is a nonfeeding stage beforemetamorphosis; often in a cocoon

eg. butterflies: larva=caterpillareg. flies: larva=maggoteg. beetles: larva=grub


once adult emerges it no longer molts

b. most of the rest have incompletemetamorphosis (hemimetabolous):

eggnymph adult

nymph resemble adult without wings

wings develop externally as budlike growths on thorax

grow by successive molts

eg. grasshoppers, cicadas, mayflies,stoneflies, dragonflies

Some insects overwinter as immature stage

don’t complete development until they areliterally frozen in winter months

Defenses

many insects have elaborate mechanisms to avoid predation

camoflage eg. walking stick

mimicry eg. viceroy butterfly

weapons eg. bombardier beetle shoots hot explosive secretions


toward predator

Diapause

some insects are able to enter a state of dormancy tosurvive adverse conditions; eg temp, humidity

if this dormancy is for an extended period andtriggered by daylength = diapause


Symbioses

coevolution with plants as pollenators

many ants and termites cultivate fungi within theirburrows

some ants guard aphids that let the ants “milk” themfor nectar-like secretions

eg. termites and protests that digest wood

eg. acacia ants


Ecological Impacts of Insects

insects are the most important organisms in mostecosystems

1. Important in Recycling of nutrients

eg. 90% of all dead animals (mainly insects) end up as food inant nests

most of the rest of the world is literally helplesswithout them

vertebrates wouldn’t last more than a few months if all insects suddenly disappeared

pollinators for most flowering plants including mostof the world’s crops


Economic Impacts of Insects

in the US a 2006 study estimates that insects directlyor indirectly contribute more than $57 Billion to oureconomy

1. as nutrition for wildlife insects contribute ~$50Billion/yr to US economy from fishing, hunting, hiking, and enjoying wildlife

2. pest controlinsects often prey on agricultural pests saving upto $4.5 billion/yr in crops and pesticides

3. Pollination services

economic value of insect pollinators worldwide is$217 Billion/yr (08)

in US, excluding honey bees, other insectpollinators contribute ~$3 Billion/yr to agriculture

4. dung beetles burying animal dung help to recyclenutrients, fertilize the soil, and reduce flies and disease carrying insect on grazing land at a value in US of $380 million/yr

5. commercial products


eg. chitinsecond most abundant organic polymercan be used to coat fruits to slow ripening

eg. beneficial insectsladybugs, etc for natural pest control

6. Venomous Insects

ants, bees, wasps, hornets, blister beetles, etc

some caterpillars have poisonous hairs or spinesthat are attached to poison gland

with any contact spine penetrates skin andinjects poison

eg. asp or pus caterpillar

spines remain poisonous even after they areshed

7. Parasites & Diseases & Vectors

8. Medical applications

maggots used to eat dead tissue from wounds

secrete a fluid containing enzymes that speed healing

will eat and remove ONLY the dead and damaged tissuesand leave the healthy tissues alone

heal some kinds of wounds much more effectively and muchmore quickly than other treatments


have produced a prototype gel that healed wounds more quickly

hope to produce wound dressings impregnated with the enzymes

Future Applications

1. blood sucking insect, Dipetalogaster maximus,is used as a high tech syringe

can take up to 4 ml in one meal

donor doesn’t feel a thing

used as a way to get blood samples from wild animals thatare difficult to sample in other ways

eg. can measure stress hormone levels in nesting terns without having to capture them

eg. used to survey rabies infections in batsremoves blood sample using a needle; theyrecover quickly

2. insects as chemical detection devices

insects have extremely sensitive olfactory senses

military and security services need ultra sensitive, flexible and portable odor detectors

sniffer dogscost ~$15,000 each,takes 6 months to trainrequire dedicated handler

“wasp hound” = a portable hand held odor detector

with a team of black wasps as its sensor


so far the wasps have learned to respond tojust about any odor tried

wasps show coiling behavior when they detectfood molecules

other insects (eg. bees) when they detect foodthey stick out their tongues

they can detect an odor at concentrations of afew ppt

equivalent to finding a grain of saltin a swimming pool

after a couple day stint as sniffers they arereturned to hive and a new batch is trained

can also be used toassure food quality,check for contaminantsmaybe even help diagnose diseases such as

cancer or TB

3. Scientists hope to harness the activities of termitebacteria to break down cellulose to produce ethanol and biofuels

Documents

Arthropods - General