Meet the ArthropodsInsects, Spiders, and Their Relatives

What’s an arthropod?An arthropod is an animal that:

Is an invertebrate (has no backbone or spinal chord)

Has jointed limbsHas a segmented bodyHas an external skeleton

(exoskeleton) made of a substance called “chitin”

Arthropods Are EverywhereYou can find arthropods everywhere: in a yard, on a street, in a pond, in the sea.

So what are they?

This creature is an ant, which is an insect. Insects are a kindof arthropod that have three body divisions (head, thorax, and abdomen) and six legs.

The feelers on its head don’t count as legs.

Yes

No

This beetle has a segmented body, an exoskeleton, and six jointed legs.

Is it an insect?

Where are the beetle’s legs?Circle them.

Most insects are larvae before they become full grown.

Larvae include the grubs and caterpillars that you may have seen in a garden. Later they mature into adult insects.

Butterflies and moths are insects.

They have six legs.

When butterflies and moths first hatch from their eggs, they are caterpillars. But they are still insects.

Yes

No

When the hornworm moth is a larva, it looks like the picture below.

Is it still an insect?

Arachnids are another kind

of Arthropod.Spiders are arachnids. arachnids are a kind of arthropod that have two body sections (cephalothorax and abdomen) and eight legs.

This creature is a raft spider.

Scorpions are also a kind of arachnid.

Besides their legs, arachnids also have other appendages, which do different things, depending on the kind of arachnid.

The scorpion is an arachnid that has eight legs. It also has a pair of claws.

How many legs does a spider have?

6

8

12

Circle the spider.

Another common class of arthropods are crustaceans.Crustaceans have several body segments that are grouped into a head, a thorax, and an abdomen. The head and thorax may be fused into one piece, and the whole body may be covered by a carapace. Crustaceans have at least 10 legs.The crab on this slide is a crustacean.

You may have eaten a crustacean.

Most crustaceans live in water. Lobsters, crabs, shrimp, crayfish, and barnacles are crustaceans. A few live on land, like woodlice.

Which animal is a crustacean?

Scorpion

Shrimp

Moth

There are other kinds of arthropods.

For example, there are the myriapods, which include centipedes. Centipedes have a pair of legs for every segment of their bodies.

Circle the insects.

How many legs does a crustacean have?

6

At least 10

8

Draw a circle around the arthropod that is not an insect, an arachnid, or a

crustacean.