Insects, Spiders and Kin

These animals (along with crabs, shrimp, crayfish and others) are arthropods—invertebrates with “jointed legs.” Most of us recognize arthropods when we see them, but here are some basic ways to start grouping them.

Centipedes, millipedes and sowbugs all have elongated bodies with many similar segments and many legs.

Spiders, ticks, scorpions and daddy longlegs all have eight walking legs—often with extra appendages near the head for manipulating food.

Insects—a group staggering in numbers and diversity—all have six legs, and their bodies are divided into three portions: head, thorax and abdomen. The adults often have one or two pairs of wings, and one pair of antennae. Several insect groups undergo a striking change (metamorphosis) between juvenile forms and winged, adult forms.

There may be as many as 10 million species of insects alive on earth today, and they probably constitute more than 90 percent all animal species. Scientists are busy cataloging and describing new insect species.

Insects are divided into orders, or major lineages, such as “the dragonflies and damselflies” and the “grasshoppers, crickets, and katydids.”

The four largest orders of arthropods

  1. The beetles, which you can quickly recognize by the two shell-like covers (actually, they’re a modified first pair of wings) that meet in a straight line down the back.
  2. The butterflies and moths, which all have tiny scales on their wings.
  3. The flies, which all have only one pair of wings. This group includes houseflies, mosquitoes, midges and gnats.
  4. The ants, bees and wasps have two pairs of wings (queen ants have wings though workers do not) and a selection of other characteristics, often with the ability to sting and a range of colonial behaviors.

Amazing diversity, immeasurably important to people

  • Many are crop pests, but insects are also crucial for pollinating nearly every flowering plant on earth.
  • They are the food source for thousands of vertebrates: Fish, amphibians, reptiles, birds and mammals rely on them, directly or indirectly.
  • Many humans eat insects, too; if not directly, then indirectly by consuming animals that eat insects.
  • Insects parasitize nearly every type of animal, including humans; mosquitoes are dreaded worldwide for the diseases they carry. A few spiders in our state deliver venomous bites to people.
  • Spiders, ladybugs, lacewings, mantids, robber flies, dragonflies and many others provide natural pest control.
  • Termites destroy wooden structures.
  • Bees make honey; fruit flies are used in genetics research; hellgrammites and crickets are used a fishing bait; silkworms make silk.
Photo of a Xysticus crab spider, individual, on rough blazing star flowerhead.


Get to know and appreciate Missouri's most common spiders.

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