Arthropods. VIII. Phylum Arthropoda By nearly any measure, the most successful animals on the planet...

Arthropods

VIII. Phylum Arthropoda

By nearly any measure, the most successful animals on the planet are the arthropods. They have conquered land, sea and air, and make up over three-fourths (71-75%) of all currently known living and fossil organisms, or over one million species in all. Once you see what organisms are arthropods, it’s easy to understand why they are so numerous…

While arthropods very greatly in many ways, they all share three basic characteristics: jointed appendages, a segmented body, and an exoskeleton. The number of legs and body parts varies by class.

Insects have three distinct body segments: head, thorax, and abdomen.

In crustaceans like crayfish, crabs, and lobsters, the head and thorax are fused into a cephalothorax. The “tail” is the abdomen.

Arachnids like spiders also have a cephalothorax.

Insects

Arachnids Crustaceans

Having a hard exoskeleton provides good protection. But it can be a disadvantage when an arthropod is growing. Arthropods must shed their exoskeleton and grow a new, larger one. As an arthropod grows, its exoskeleton splits along the back of the thorax. The arthropod can then crawl out of its old exoskeleton. This process is called “molting.”

http://www.youtube.com/watch?v=2A1i10ZIB-w

Because there are so many different types of arthropods, there are also many different ways in which they develop and grow. Most begin as eggs, hatch into larvae, and then metamorphose (change) into adults. There are two types of metamorphosis:

In incomplete metamorphosis, the newly hatched arthropod looks very much like the adult version. There is no larval stage. The middle stage is the nymph stage.

In complete metamorphosis, the newly hatched arthropod goes through a larval stage, then a pupal stage before finally developing into the adult.

ELPAENA

Some insects undergo complete metamorphosis, like this butterfly. What are the four stages of complete metamorphosis?

Moths, butterflies, ants, bees, termites

http://www.youtube.com/watch?v=AZk6nZGH9Xo

Some insects undergo a type of incomplete metamorphosis. For insects that have aquatic nymphs, the nymph stage bears little resemblance to the adult. For insects with terrestrial nymphs, the nymphs look very much like the adult only smaller and generally wingless. This is also referred to as “gradual metamorphosis.”

http://www.youtube.com/watch?v=NutMWUlca-o

Grasshoppers, crickets, praying mantises, katydids.

aquatic

No pupa stage. The adult emerges from the nymph by molting once it reaches a certain size.

Dragonflies, mayflies, flies, damsel flies

http://www.youtube.com/watch?v=TzF0GKfOvRY

A. Millipedes and Centipedes (terrestrial)

Millipedes are herbivorous and generally harmless, although they can squirt some stinky stuff as a defense mechanism.

They have one pair of antennae, and usually two pairs of legs per body segment (“mili” means 1000, but they don’t have that many legs.)

They are non-venomous, have many body segments and feet, and are generally not considered a source of food for humans.

But you never know…

http://www.youtube.com/watch?v=NAnc1jA-050

Centipedes are predators. They will eat other arthropods or even small vertebrates.

They generally have one pair of legs per body segment and one pair of antennae.

They can inflict a painful bite, but are non-venomous.

They are not a source of food for humans.

http://www.youtube.com/watch?v=TzF0GKfOvRY

B. Arachnids (mostly terrestrial)

If there were a popularity contest for arthropods, arachnids would come out on bottom in most votes. That’s because many arachnids are nasty parasites, and some are venomous.

As we already learned, arachnids have 8 legs, two main body parts (cephalothorax and abdomen) and no antennae.

Arachnids like ticks, mites, and chiggers are parasitic. Several species can carry diseases like Lyme Disease and Rocky Mountain Spotted Fever (ticks).

Spiders and scorpions, or course, are venomous. ALL spiders are venomous, however, only a handful present a significant risk to humans.

1. Spiders

Spiders are important predators. They feed primarily on other arthropods, however, some species of spider are large enough to feed on small vertebrates such as frogs. Spider venom can attack the prey’s autonomic nervous system causing it to shut down. Spider venom also can cause necrosis, the death and decay of tissue. Spiders don’t generally “eat” their prey. They “drink” it. The necrotizing venom softens the tissue and eventually liquifies it.

All spider bites can be painful and cause swelling, irritation, and infection. But the bites from two of the world’s most infamous arachnids should always be treated medically. Those two spiders are abundant in Georgia.

The Black Widow spider often lives under rocks and in crevices. They are fairly easy to identify. They have a glossy, large, black abdomen with a red hourglass on the ventral (bottom) side of the abdomen. Black Widow venom is a neurotoxin, a poison that attacks the victim’s nervous system. An effective anti-venom was developed in 1956, but the anti-venom can only be given to victims who are certain they have been bitten by the Black Widow. Giving the wrong anti-venom can be very dangerous.

http://www.youtube.com/watch?v=wcdKlgFOPsQ

The bite of the Black Widow is often not painful and may go unnoticed. But the poison injected by the Black Widow bite can cause abdominal pain similar to appendicitis as well as pain to muscles or the soles of the feet. Other symptoms include alternating salivation and dry-mouth, paralysis of the diaphragm, profuse sweating and swollen eyelids.

The Brown Recluse spider is another common and very dangerous spider. The Brown Recluse’s venom has a powerful necrotizing agent. Immediately after being bitten, the victim’s tissue near the bite site begins to die and decay. As this happens, the bite site becomes an area where bacteria begin to spread rapidly causing a secondary infection in the victim.

Like the Black Widow, the Brown Recluse has a tell-tale identifier. On the dorsal (top) side of its cephalothorax, the Brown Recluse has a mark that is shaped like a violin or “fiddle.”

http://www.youtube.com/watch?v=OrFtyRcDNUU

Graphic

Image

Warning

Progression of necrosis following a Brown Recluse bites.

Never, never, never, never, never……..neglect a spider bite. The longer you wait to seek medical attention, the more serious the damage.

FemaleMale

For more on the risk of local spiders, visit:

http://www.termite.com/spider-identification.html

Although tarantulas often evoke panic and anxiety on sight, these hairy long-legged spiders generally are non-aggressive and rarely bite. Tarantula venom is rarely toxic to humans; bites from tarantula species in the United States can be painful but are not considered dangerous.

Wolf Spider

Garden Spiders with their signature zig-zag web.

Many soldiers who served in Iraq became familiar with this monster, the Camel Spider.

2. Ticks and Mites

Ticks and mites are parasitic arachnids that feed on the blood the host species. While not venomous, ticks are non-venomous, however, several species of ticks are carriers of diseases. If the tick is removed within 24 hours. You will usually be ok.

http://www.youtube.com/watch?v=0wotB38WrRY

Chiggers are the larval stage of a type of mite. Chiggers can infect a person’s body and cause a rash and serious itching. Chiggers actually don’t feed on blood. They are so small, the feed on fluids in skin cells.

Billions of dust mites live in our homes. They feed off tiny particles of dead skin that constantly slough off our body. The feces of this animal is one of the most common sources of indoor allergy.

Eyelash mites…..

https://www.youtube.com/watch?v=47CIdUld8eQ

3. Scorpions

Scorpions are also venomous, but their venom is often the victim of urban legend. Scorpion venoms are complex mixtures of neurotoxins (toxins which affect the victim's nervous system) and other substances; each species has a unique mixture. Despite their bad reputation, only one species in the western U.S. (the bark scorpion) and about 25 others worldwide have venom potent enough to be considered dangerous to humans.

Striped Bark Scorpion

Emperor Scorpions

Complete a Venn Diagram for arachnids vs. insects using the following characteristics:

1. Number of body segments2. # of appendages3. Name of body segments4. # antennae5. Capable of flight or not 6. Have species that are venomous.7. Jointed appendages?8. Segmented bodies?9. Exoskeleton?

10. Identify two insects that undergo complete metamorphosis:

11. Identify two insects that undergo incomplete metamorphosis:

C. Crustaceans (mostly aquatic; mostly marine)

Crustaceans are the group of arthropods that are most commonly recognized as food for humans (although we will see later that insects also fill that role in many countries.) Crustaceans include lobsters, crabs, shrimp, and crayfish.

Other crustaceans like copepods and krill are enormously important in the marine food chain.

Most crustaceans have two main body parts (cephalothorax, abdomen), 5 or more pairs of appendages, and two sets of antennae (one long, one short.

1. Lobsters and Crayfish

Maine Lobster

Spiny lobster

Cornish Lobster

Maine lobster makes a major contribution to the state's economy. In 2006, the catch exceeded 72 million pounds and generated close to $300 million.

Crayfish…crawfish….crawdads…whatever….

2. Shrimp, Prawns, Krill, Copepods (mostly marine)

Shrimp and prawns are only slightly different, so the two are generally treated as the same when it comes to recipes. There are large species of freshwater or brackish water prawn, but freshwater shrimp are very small.

Krill and copepods are not eaten by humans, but they are one of the most important sources of food for many species of marine animals, particularly in colder waters. Krill and copepods feed on algae and other small organisms.

The shrimping industry in Georgia used to be a multi-million dollar industry. Competition from cheap, farm raised shrimp couple with high gas prices has crippled Georgia shrimping. Many shrimpers can no longer leave the dock.

http://savannahnow.com/news/2011-07-31/georgia-savannah-shrimpers-catch-hardship-hope

Article

Dirty bag shrimp

The largest animal to ever live feeds on the shrimp-like krill. Krill cloud the water in the spring in colder waters, providing rich nourishment for many species of animal.

An adult humpback whale can eat 1-2 tons of krill a day.

http://www.youtube.com/watch?v=1_BqC9IIuKU

Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat and they constitute the biggest source of protein in the oceans.

There are approximately 7500 species of copepod, with nearly 2000 being parasitic.

Sea lice are parasitic

Brine shrimp

Sand fleas can make a day at the beach miserable. They have a painful bite, but are very tiny.

Cyclops larvae

cyclops

Diaptomoushttp://www.youtube.com/watch?v=GDeY6snQw6s

3. Crabs

There are many species of crab, though not all are edible.

The crab with the largest span is the Japanese Spider Crab.

The crab fishery in Alaska is a huge industry, with separate seasons for the different species like…

King Crab

Dungeness

Opilio (Snow Crab)

In the Atlantic, fisheries include blue crab, stone crab, and rock crab.

Another large and strange looking crab is the terrestrial Coconut Crab, the largest crab by weight or bulk.

http://www.youtube.com/watch?v=ch3VVI4IDqc

And then there are, of course, the hermit crabs. Many of these species are terrestrial.

During the mating season, terrestrial red crabs stampede to the ocean where they must lay there eggs.

https://www.youtube.com/watch?v=WSkj5IH6qMU

https://www.youtube.com/watch?v=LNKgh6TfWXo

If you see little holes near the dunes at the beach, they were probably made by Ghost Crabs.

In the marshes, Fiddler Crabs dig burrows in the mud below the water line. (But not ones this cool looking.)

The abominable snow crab!? Well, yeah—in a manner of speaking. This deep sea dweller was discovered a couple miles down in 2005 and called the Yeti Crab.

Note to Sponge Bob Square Pants fans…

Krabby Patties contain no crabmeat.

So, is anyone hungry yet? Yes? GREAT!

Because next we’re going to talk about the last but most numerous invertebrate. These scrumptious little bites are a major source of protein in many parts of the world.

Open wide, ‘cause here come the…

Insects!

D. InsectsThere are approximately 800,000 species of insects on the planet, and more are being discovered every day.

Insects are found in almost every environment on Earth. They can be saprophytic scavengers, parasites, herbivores, or predators.

While there are thousands of different shapes, sizes, and body designs, all insects have several important traits in common. In addition to having the typical arthropod characteristics of jointed appendages, exoskeletons, and segmented body parts, insects can be distinguished from other arthropods by these traits:

•Insects have three pairs of legs

• Insects have three body parts: head, thorax, and abdomen

•Insects are the only arthropods capable of true flight

•Insects have one set of antennae

•Some insects are social insects that live in colonies (bees, ants, termites, etc.) while others lead mostly solitary lives (grasshoppers, butterflies, flies, etc.)

http://www.youtube.com/watch?v=lE-8QuBDkkw

Colony Collapse Disorder-

Colony Collapse Disorder (CCD) is a serious problem threatening honey bees throughout the world. Entire hives are disappearing. It is estimated that 30% of the world’s plants (including many that we use as food) rely on bees to pollinate.

While it is not known for certain what is causing CCD, suspects include parasitic mites and a type of bee virus. Since none of the bees that are reported to have disappeared are found dead around the hive, it has been very difficult for scientists to autopsy the bees to help understand the problem better.

http://www.youtube.com/watch?v=unca1QR3nLs

Lacewing design, Thin, membranous. Generally has a system of “veins” running through them.

The wings of butterflies and moths are covered in tiny scales and sometimes a powder-like substance

Insects like beetles have two pairs of wings, but the top pair is a flightless shell or cover that protects the insect when it is not in flight.

EXTION INFORMATION

Most insects have two pairs of wings. Some, like flies, gnats, and mosquitoes, have one pair. A minority of species are wingless such as ants and termites (although there are species of both ants and termites that can produce winged members that “swarm” during certain times of year.)

Top “wings”

Spiders have simple eyes, but they have 8 of them. Insects and many crustaceans have simple eyes AND compound eyes. Compound eyes are eyes that have many lenses or facets.

Dragonfly nymph

Adult caddis fly

Sometimes it is really hard to tell some of these guys apart. Which is the grasshopper? The cricket? The katydid?cricket

grasshopper

katydid

Remember from our early lessons that many insects use mimicry as a means of camouflage. http://

www.youtube.com/watch?v=EJGtN-igCu8http://www.youtube.com/watch?v=EX9ySwi-kHQ

The largest insect is probably the Goliath Beetle.

But the acteon is no slouch.

Acteon grub (larvae). Yes, they do eat them.

Giant weta of Australia

It’s hard to say what insect species in the biggest. The Borneo Walking Stick definitely gets the prize for length, but girth?

Our local “giants” include the Eastern Lubber Grasshopper and…

…the Giant Water Bug, aka “toe biter.”

Anybody hungry?

Silkworm larvae stir fry

Grasshoppers on the Bar-B.

Fried? In a soup? There are countless ways to prepare these delicious arthropods!!!