Insects, Spiders, Crayfish & More

Insects, spiders and crustaceans (flies, beetles, ants, ticks, daddy long legs, centipedes, pill bugs, crayfish, etc.) are members of the largest category of creatures on the planet: arthropods.

Arthropods have hard, external shells called “exoskeletons,” segmented bodies and jointed legs. (The word "arthropod" comes from the Greek words for “joint” and “foot.”)

Insect, Bug or Other?

When talking about small arthropods that crawl or fly around basements, gardens and forest preserves, many people use the word "bug," but "bug" covers just one group.

If the arthropod in question has three pairs of jointed legs, a three-part body, compound eyes and two antennae, it's an "insect." Familiar insects include bees, wasps, beetles, mosquitoes, flies, grasshoppers, ants, butterflies, moths, dragonflies and damselflies.

An insect's a "true bug" only if it has a certain type of sucking mouthpart called a “stylet.” Cicadas, aphids and leafhoppers are all true bugs. All true bugs are insects, but not all insects are true bugs, and you can't rely on common names to tell who's who. Lightning bugs, June bugs and ladybugs are all insects, but because they don't have the right mouthparts none are "true bugs."

One large group of arthropods often lumped in with "bugs" aren't insects at all. Spiders, harvestmen, ticks and mites are all "arachnids." Most adults have eight legs and two-part bodies, although on ticks and harvestmen (aka daddy longlegs) the two parts are joined so closely they look like single ovals.

Equally "buggy" to some are centipedes and millipedes — "myriapods" from the Greek for "10,000" and "foot" — although these multilegged arthropods are certainly not insects. (Common name aside, though, most centipedes in your basement likely have only 30 legs).