Hexapods represent the most successful body plan in the history of terrestrial life. The name Hexapoda literally translates to “six feet,” which is the defining characteristic of this group. Unlike other arthropods like spiders (eight legs) or centipedes (many legs), hexapods have a body strictly divided into three sections: a head, a thorax (where the legs and wings are attached), and an abdomen. While the vast majority of hexapods are true insects, the group also includes a few primitive lineages that branched off before insects evolved their external mouthparts.

Class Insecta — The Insects

These are arguably the most successful group of all animals. With around one million named species, they make up three-quarters of all described animal life. However, researchers estimate the actual number could be as high as 5 to 10 million species.

The word “insect” comes from the Latin insectum, meaning “with a notched or divided body.” This refers to their three distinct body segments: head, thorax, and abdomen. As six-legged arthropods, they are characterized by a pair of antennae, compound eyes, and, in most adult stages, two pairs of wings.

Orders of Insects

Modern classification, divides insects based on their evolutionary history and how they grow. Early on, a couple of groups branched off the evolutionary tree before the development of wings. They are:

• Order Archaeognatha (Jumping Bristletails)
• Order Zygentoma (Silverfish and Firebrats)

The vast majority of insects went on to develop wings and are grouped together in the Subclass Pterygota. While most possess wings as adults, the group also includes “once-winged” insects like fleas or lice that lost their wings through evolution.

Growth in this subclass generally follows one of two paths: incomplete metamorphosis, where the young look like miniature versions of the adults, or complete metamorphosis, where the insect transforms from a larva and pupa into its final adult form.

Show orders

Links to orders where I have observations

• Coleoptera — Beetles
• Hemiptera — True bugs
• Lepidoptera — Butterflies and moths
• Odonata — Dragonflies and damselflies

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Class Entognatha — The Primitive Hexapods

are mostly tiny, soil-dwelling organisms. The name refers to their entognathous mouthparts, which are retracted into a pocket within the head—a key feature that separates them from true insects. They lack wings and are often found in leaf litter or moist soil where they play a critical role in nutrient cycling.

The Three Orders

• Collembola (Springtails) – The most common group, famous for a spring-like tail (furcula) used to catapult themselves away from predators.
• Protura (Coneheads) – Tiny, blind hexapods that lack antennae and use their front legs as sensory organs.
• Diplura (Two-pronged Bristletails) – Slender, pale creatures with two long “tails” (cerci) at the end of the abdomen.

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