Introduction to Insect Taxonomic Classification

Here is a question: is a butterfly a bug? Contrary to what you might think, no, butterflies are technically not bugs. Butterflies are insects, but they lack the features necessary to be considered “true” bugs. When it comes to biology, classifications like “insect” or “bug” take on a very specific meaning that often comes apart from the common usage of the word.

Biologists who classify and name plants and animals are called taxonomists. Taxonomists use special biological categorizations to organize the diversity of life into groups that share common features, morphologies, or genetic ancestry. According to classical taxonomic theory, there are 7 hierarchical categories for classifying life.

♦ Kingdom
♦ Phylum
♦ Class
♦ Order
♦ Family
♦ Genus
♦ Species

insect taxonomy

Although many creatures get called “insects” in everyday conversation, the biological term “insect” refers specifically to invertebrate animals in the class Insecta. Insects are defined as having a chitinous exoskeleton, a three-segment body consisting of a head, thorax, and abdomen, 3 pairs of jointed legs, compound eyes, and antennae. Insects are the single most diverse grouping of animals and there are an estimated 6 to 10 million extant species. Other common characteristics of insects include development through a series of molts, a set of vestigial or functional wings, and hatching from eggs.

Cicadas are true bugs and have mouthparts for chewing. Source: B. Martin via WikiCommons CC-BY-SA 2.5
Cicadas are true bugs and have mouthparts for chewing. Source: B. Martin via WikiCommons CC-BY-SA 2.5

In contrast, the term “bug’ refers to insects that fall under the order Hemiptera. Bugs are distinguished from insects by their specialized mouthparts meant for sucking or chewing. Examples of organisms that fall under the category of true bugs include cicadas, aphids, grasshoppers, and shield bugs. Several insects that may have the word “bug” in their common name may or may not actually be bugs. Ladybugs, for example, are actually beetles, not bugs.

All bugs are insects, but not all insects are bugs. Cicadas, are bugs and are therefore also insects, but butterflies are insects and are not bugs. Of the millions of species of insects, only about 80,000 of them are considered “true” bugs. Both insects and bugs fall under that larger phylum of arthropods.

A partial phylogeny chart showing the relationship between different insect orders. Source: Public Domain

A partial phylogeny chart showing the relationship between different insect orders. Source: Public Domain

Several animals get called bugs or insects but are actually neither. Spiders, for example, are often called bugs or insects, but spiders are neither insects nor bugs. Spiders are arthropods and belong to another class of organisms called Arachnida. Other organisms included in class Arachnida include scorpions, ticks, mites, and solifugae (sometimes called “whip scorpions”). Arachnids typically have a 2-segment body and 8 legs. The forelegs of many species of arachnids are specialized for feeding, grasping, and defense. Arachnids typically do not have antennae or wings, another feature that distinguishes them from insects.

Interesting Facts About Insect Taxonomy

  • The word “Hemiptera” comes from two Greek words hemi (half) and pteron (wing). Most true bugs have hardened wings in front and softer wings on the back.
  • The word “arachnid” comes from the Greek myth of Arachne, a maiden who was turned into a spider after beating Athena in a weaving contest.
  • The phylum Arthropoda also includes crustaceans and crabs. This means that spiders are more closely related to crabs and lobsters than they are to insects.
  • Organisms like slugs and snails are often considered insects but this is false. Snails and slugs are mollusks and fall under the phylum Mollusca, the same phylum that includes octopuses and squids.