Are Centipedes Insects? The Answer and Key Differences

Centipedes are not insects. They belong to an entirely separate class of arthropods called Chilopoda, while insects belong to the class Insecta. The two groups last shared a common ancestor hundreds of millions of years ago and evolved many of their most recognizable traits independently of each other, including the ability to live on land. The confusion is understandable: centipedes are small, leggy, terrestrial creatures that scuttle across floors and hide under rocks, which is exactly what many insects do. But the biological gulf between a centipede and a beetle is far wider than it might seem when one darts out from behind your washing machine.

Where Centipedes Actually Fit in the Tree of Life

Both centipedes and insects are arthropods, the enormous phylum that also includes spiders, crabs, shrimp, and scorpions. Within that phylum, though, they sit on different branches. Insects are grouped with crustaceans in a clade called Pancrustacea, meaning your backyard ant is more closely related to a lobster than to the centipede living under the same paving stone. Centipedes belong to the subphylum Myriapoda, which they share with millipedes and a couple of lesser-known groups. Molecular estimates calibrated with fossil data place the origin of arthropods back in the Ediacaran period, with most of the major lineage splits happening during the Cambrian.

One of the most striking findings from molecular phylogenetics is that centipedes and insects became land-dwelling creatures independently. The first sequencing of a myriapod genome, from the centipede Strigamia maritima, confirmed that myriapods attained terrestriality on their own, separate from the lineage that gave rise to insects.¹ That means many of the features centipedes and insects share for surviving on land, such as tracheal breathing systems and waterproofing adaptations, evolved separately rather than being inherited from a shared terrestrial ancestor. The resemblance is convergence, not kinship.

The Obvious Physical Differences

The quickest way to tell a centipede from an insect is to count body regions and legs. An insect’s body is divided into three distinct sections: head, thorax, and abdomen. It has six legs, all attached to the thorax, and most adult insects have wings (or at least vestigial remnants of them). A centipede’s body follows a fundamentally different blueprint. It has a head followed by a long series of largely similar segments, each bearing a single pair of legs. This kind of body plan is described as homonomous, meaning the segments repeat with relatively little specialization from front to back.¹

The leg count varies enormously among centipede species but is always an odd number of pairs, ranging from 15 pairs in common house centipedes up to over 190 pairs in some soil-dwelling geophilomorphs. No centipede actually has exactly 100 legs despite what the name implies. Insects never exceed six legs in their adult form, period. There are no wings on any centipede, and there never have been in their entire evolutionary lineage.

Antennae differ too. Insects have one pair of antennae, and centipedes also have one pair, so that feature alone won’t help you distinguish them. But insects have compound eyes made of hundreds or thousands of tiny lenses, giving many species excellent vision. Most centipedes have simple eye clusters called ocelli, and some soil-dwelling species have no eyes at all. The house centipede (Scutigera coleoptrata) is an exception with large, well-developed compound eyes, but even those are structured differently from insect compound eyes.

Forcipules and Venom

Perhaps the most remarkable feature unique to centipedes is their forcipules: a pair of modified front legs that have been repurposed into venom-injecting fangs. This is the only known case in the entire animal kingdom of walking legs evolving into venom-delivery apparatus.² Insects that inject venom do it through stingers (modified egg-laying organs, as in bees and wasps) or through mouthparts (as in some assassin bugs). No insect uses converted legs for the job.

Centipede venom is far more complex than researchers initially expected. Studies cataloguing the protein and peptide families in centipede venom have identified at least 61 distinct evolutionary lineages of venom components. Many of these bear no resemblance to any previously characterized protein family, meaning they are genuinely novel biochemistry.³ Some centipede venom proteins have been convergently recruited into the venoms of unrelated animals like spiders and scorpions, which tells evolutionary biologists something about which molecular tools are especially useful for subduing prey. The venom is toxic to both mammals and insects, which makes centipedes effective predators of the very creatures people confuse them with.⁴

For humans, most centipede bites cause localized pain and swelling comparable to a bee sting. Large tropical species in the order Scolopendromorpha can produce more serious symptoms, and the diversity of their venom proteins helps explain why reactions occasionally go beyond simple pain.³ No centipede species is considered life-threatening to healthy adults, but the bites of the largest species deserve medical attention.

How They Breathe

Both centipedes and insects breathe through tracheal systems: networks of branching tubes that deliver oxygen directly to tissues without relying on blood to carry it, the way vertebrates do. This sounds like a strong similarity, but the details diverge significantly, and the systems almost certainly evolved independently.

In insects, paired spiracles (breathing pores) line the sides of the body, typically on the thorax and abdomen segments. Air enters through these openings and travels through progressively smaller tubes until it reaches individual cells. Most centipede orders (the pleurostigmophoran centipedes) also have lateral spiracles, but house centipedes and their relatives in the order Scutigeromorpha do something unusual. Their spiracles are unpaired and sit on the dorsal (top) surface of the body instead. Research on the tracheal systems of five different scutigeromorph species found that while all five were remarkably similar to each other, their architecture was distinctly unlike what is seen in other centipede orders.¹ This has fueled an ongoing debate about whether tracheal systems evolved once or multiple times within centipedes alone, let alone between centipedes and insects.

Centipedes are generally more vulnerable to drying out than insects are. Most insects have a waxy cuticle layer that limits water loss very effectively, which is one reason they have colonized deserts, high altitudes, and open grasslands so successfully. Centipedes, by contrast, tend to stick to moist habitats: soil, leaf litter, under logs and stones, in caves. Their cuticle is less waterproof, and their breathing system can lose moisture more readily. This is why you almost never see centipedes out in the open during the day.

Internal Plumbing Is Surprisingly Similar

Despite the evolutionary distance between them, centipedes and insects share some internal features that turn out to be older arthropod traits rather than insect-specific inventions. A clear example comes from the Malpighian tubules, the waste-processing structures that function a bit like simplified kidneys. Research on the centipede Lithobius forficatus found that its Malpighian tubules produced a potassium-enriched fluid and maintained a positive electrical potential across the tubule wall, both characteristics long thought to be exclusive to insects.⁵

There were differences, too. Insect Malpighian tubules typically rely heavily on potassium to drive fluid secretion, while the centipede’s tubules were strongly sodium-dependent instead. But the broader finding is significant: traits that textbooks once held up as uniquely insect adaptations to terrestrial life turn out to be shared with non-insect arthropods. The implication is that some of these physiological mechanisms are ancient enough to predate the split between myriapods and the line that led to insects, or they evolved convergently because they solve the same physical problem.⁵

Development and Regeneration

Insects and centipedes grow up very differently. Most insects go through metamorphosis: either a complete transformation from larva to pupa to adult (like butterflies) or a gradual series of nymph stages that increasingly resemble the adult (like grasshoppers). Centipedes don’t undergo metamorphosis. Instead, they hatch either with their full complement of legs already in place (as in the order Scolopendromorpha) or with fewer legs than the adult and add segments and leg pairs with each successive molt, a process called anamorphic development.

The regeneration abilities of centipedes set them further apart. House centipedes are famous for shedding their legs when grabbed by a predator, much as some lizards drop their tails. What happens next is impressive. Research has classified centipede limb regeneration into two categories: progressive regeneration, where a lost limb gradually returns to normal over several molting cycles, and explosive regeneration, where the full-sized, fully functional leg comes back after a single molt.⁶ House centipedes in particular exhibit explosive regeneration. If a leg is lost before a critical point roughly seven days before the next molt, it can be completely restored in one molting cycle.⁶ While a few insects can regenerate limbs during their nymphal stages, nothing in the insect world matches the speed and completeness of house centipede leg regeneration.

Parental Care

If you think of arthropod parenting as something mostly limited to social insects like ants and bees, centipedes have a surprise for you. Many centipede species in the order Scolopendromorpha practice maternal care, with the mother coiling her body around her clutch of eggs and remaining with the young after they hatch. She guards the brood, keeps it clean (likely preventing fungal infection), and in some species may not eat for weeks during the brooding period.

Field observations from São Sebastião Island in southeastern Brazil documented females of Otostigmus scabricauda guarding both eggs and first-instar nymphs, the first field report of maternal care in a Neotropical centipede species.³ This kind of brooding is not rare among scolopendromorphs and has been observed in multiple species worldwide. It is a genuine investment: if the mother is disturbed, she may abandon or even eat the clutch. The behavior has no real parallel among most solitary insects, where eggs are typically deposited and left to fend for themselves. Earwigs are one of the few non-social insects known to guard their young, which gives you a sense of how unusual this behavior is across the broader arthropod world.

Ecological Roles and Habitat Preferences

Centipedes are almost exclusively predators. They eat insects, spiders, worms, and other small invertebrates, which places them in a fundamentally different ecological position than most insects. Insects occupy an extraordinary range of ecological niches: pollinators, decomposers, herbivores, parasites, predators, and more. Centipedes are specialists by comparison, and they fill the predator role in soil and leaf-litter food webs in ecosystems around the world.

Research in tropical montane forests of the Andes tracked how centipede communities shift across different stages of forest succession. Temperature fluctuations and prey availability were the strongest factors driving centipede abundance overall, but different centipede orders responded to different variables. Scolopendromorpha (the large, robust centipedes) were most strongly associated with maximum temperature, while geophilomorphs (slender, eyeless soil centipedes) were linked to a combination of prey availability, temperature variation, and slope of the terrain.³ The finding that different centipede lineages respond to entirely different environmental drivers highlights how diverse their ecology is, even within a single group often lumped together as “just centipedes.”

Their sensitivity to moisture means centipedes are useful indicators of habitat quality in forests and soils. A patch of ground teeming with centipedes is almost certainly moist, well-structured, and rich in prey. Heavily degraded or dried-out soils tend to have fewer centipede species, which in turn may mean reduced predation pressure on the small invertebrates that break down organic matter.

What About Millipedes?

If centipedes aren’t insects, people often wonder whether they’re the same thing as millipedes. They aren’t, though both are myriapods. Millipedes belong to the class Diplopoda and differ from centipedes in several fundamental ways. Millipedes have two pairs of legs per visible body segment rather than one, move slowly, and are mostly detritivores that feed on decaying plant matter. They lack venom entirely and defend themselves through chemical secretion rather than biting. Their bodies are typically cylindrical and hardened, built for pushing through soil rather than chasing prey.

Centipedes, by contrast, are fast, flattened predators with one pair of legs per segment and those signature venom-injecting forcipules. The two groups are thought to have diverged from each other very early in myriapod evolution, so despite looking superficially similar to someone unfamiliar with them, they are as different from each other as cats and dogs are within mammals. The main thing they share, besides both being myriapods, is a preference for damp, dark habitats.

Why the Confusion Persists

Part of the reason people lump centipedes in with insects is cultural rather than biological. Pest control companies market services against “insects and bugs” and include centipedes in the same breath as ants, roaches, and spiders. Hardware stores stock insecticides alongside glue traps, and the packaging often shows centipedes on the same label as beetles. In everyday language, “bug” and “insect” function as catch-all terms for any small terrestrial invertebrate, and centipedes get swept in by default.

There is also a practical reason the confusion sticks: many of the products that kill insects also kill centipedes, because both groups share enough physiology (tracheal breathing, chitinous exoskeletons, similar nervous-system chemistry) that broad-spectrum pesticides affect them in comparable ways. So from a homeowner’s perspective, the distinction between an insect and a centipede may feel academic. But it isn’t, especially if you’re trying to understand why you have centipedes in your house in the first place. Centipedes show up because their prey is there. A house centipede population in your bathroom is a sign that other small arthropods are present in enough numbers to sustain a predator. Getting rid of the centipede without addressing its food source is like removing the smoke alarm without looking for the fire.

Living Fossils or Quietly Evolving?

Centipedes are sometimes called living fossils, and the label isn’t entirely unfair. Recognizable centipede fossils date back to the Silurian period, over 400 million years ago, making them among the oldest known land-dwelling arthropods. Their body plan has remained relatively conservative over that span. The myriapod genome project found that Strigamia maritima retains a surprisingly conservative set of genes compared to insects, which have undergone much more dramatic gene family expansions and losses.¹

But “conservative” does not mean static. Centipede venom, for instance, is anything but primitive. The 61 or more distinct venom protein families represent a long evolutionary history of diversification, with many families having no counterpart in any other known organism.³ The fact that centipedes look similar to their ancient ancestors externally while quietly innovating in their biochemistry is a reminder that evolution doesn’t always express itself in ways we can see. Insects are flashier about their evolutionary creativity: wildly varied wing shapes, social colonies, metamorphosis. Centipedes have been more subtle, refining a body plan that worked well 400 million years ago while evolving one of the most complex venom cocktails in the invertebrate world.