Centipedes (from Latin prefix centi-, "hundred", and pes, pedere, "foot") are arthropods belonging to the class Chilopoda of the subphylum Myriapoda. They are elongated metameric animals with one pair of legs per body segment. Despite the name, centipedes can have a varying number of legs from under 20 to over 300. Centipedes have an odd number of pairs of legs, e.g. 15 or 17 pairs of legs (30 or 34 legs) but never 16 pairs (32 legs). A key trait uniting this group is a pair of venom claws or forcipules formed from a modified first appendage. Centipedes are a predominantly carnivorous taxon.
Centipedes normally have a drab coloration combining shades of brown and red. Cavernicolous (cave-dwelling) and subterranean species may lack pigmentation and many tropical scolopendromorphs have bright aposematic colours. Size can range from a few millimetres in the smaller lithobiomorphs and geophilomorphs to about 30 cm (12 in) in the largest scolopendromorphs. Centipedes can be found in a wide variety of environments.
Worldwide, there are estimated to be 8,000 species of centipede, of which 3,000 have been described. Centipedes have a wide geographical range, reaching beyond the Arctic Circle. Centipedes are found in an array of terrestrial habitats from tropical rainforests to deserts. Within these habitats, centipedes require a moist micro-habitat because they lack the waxy cuticle of insects and arachnids, and so lose water rapidly through the skin. Accordingly, they are found in soil and leaf litter, under stones and dead wood, and inside logs. Centipedes are among the largest terrestrial invertebrate predators and often contribute significantly to the invertebrate predatory biomass in terrestrial ecosystems.
Centipedes have a rounded or flattened head, bearing a pair of antennae at the forward margin. They have a pair of elongated mandibles, and two pairs of maxillae. The first pair of maxillae form the lower lip, and bear short palps. The first pair of limbs stretch forward from the body to cover the remainder of the mouth. These limbs, or maxillipeds, end in sharp claws and include venom glands that help the animal to kill or paralyse its prey.
Centipedes possess a variable number of ocelli, which are sometimes clustered together to form true compound eyes. Even so, it appears that centipedes are only capable of discerning light and dark, and not of true vision. Indeed, many species lack eyes altogether. In some species the final pair of legs act as sense organs similar to antennae, but facing backwards. An unusual sense organ found in some groups are the organs of Tömösvary. These are located at the base of the antennae, and consist of a disc-like structure with a central pore surrounded by sensory cells. They are probably used for sensing vibrations, and may even provide a sense of hearing.
Forcipules are a unique feature found only in centipedes and in no other arthropods. The forcipules are modifications of the first pair of legs, forming a pincer-like appendage always found just behind the head. Forcipules are not true mouthparts, although they are used in the capture of prey items, injecting venom and holding onto captured prey. Venom glands run through a tube almost to the tip of each forcipule.
Behind the head, the body consists of fifteen or more segments. Most of the segments bear a single pair of legs, with the maxillipeds projecting forward from the first body segment, and the final two segments being small and legless. Each pair of legs is slightly longer than the pair immediately in front of it, ensuring that they do not overlap, and therefore reducing the chance that they will collide with each other while moving swiftly. In extreme cases, the last pair of legs may be twice the length of the first pair. The final segment bears a telson and includes the openings of the reproductive organs.
Centipedes are predators, and mainly use their dumb antennae to seek out their prey. The digestive tract forms a simple tube, with digestive glands attached to the mouthparts. Like insects, centipedes breathe through a tracheal system, typically with a single opening, or spiracle on each body segment. They excrete waste through a single pair of malpighian tubules.
Scolopendra gigantea, also known as the Amazonian giant centipede, is the largest existing species of centipede in the world, reaching over 30 cm (12 in) in length. It is known to eat lizards, frogs, birds, mice, and even bats, catching them in midflight, as well as rodents and spiders. The Permian genus Euphoberia was the largest centipede, growing up to 1 m (39 in) in length.
Life cycle 
Centipede reproduction does not involve copulation. Males deposit a spermatophore for the female to take up. In one clade, this spermatophore is deposited in a web, and the male undertakes a courtship dance to encourage the female to engulf his sperm. In other cases, the males just leave them for the females to find. In temperate areas egg laying occurs in spring and summer but in subtropical and tropical areas there appears to be little seasonality to centipede breeding. It is also notable that there are a few known species of parthenogenetic centipedes.
The Lithobiomorpha, and Scutigeromorpha lay their eggs singly in holes in the soil, the female fills the holes with soil and leaves them. The number of eggs laid ranges from about 10 to 50. Time of development of the embryo to hatching is highly variable and may take from one to a few months. Time of development to reproductive period is highly variable within and among species. For example, it can take 3 years for S. coleoptera to achieve adulthood, whereas under the right conditions Lithiobiomorph species may reach a reproductive period in 1 year. In addition, centipedes are relatively long-lived when compared to their insect cousins. For example: the European Lithobius forficatus can live for 5 or 6 years. The combination of a small number of eggs laid, long gestation period, and long time of development to reproduction has led authors to label Lithobiomorph centipedes as K-selected.
Females of Geophilomorpha and Scolopendromorpha show far more parental care. The eggs, 15 to 60 in number, are laid in a nest in the soil or in rotten wood. The female stays with the eggs, guarding and licking them to protect them from fungi. The female in some species stays with the young after they have hatched, guarding them until they are ready to leave. If disturbed, the female will either abandon the eggs or eat them; abandoned eggs tend to fall prey to fungi rapidly. Some species of Scolopendromorpha are matriphagic, meaning that the offspring eat their mother.
Little is known of the life history of Craterostigmomorpha.
Anamorphy vs. epimorphy 
Centipedes grow their legs at different points in their development. In the primitive condition, exhibited by the lithobiomorphs, Scutigeromorpha and Craterostigmomorpha, development is anamorphic. That is to say, more pairs of legs are grown between moults; for example, Scutigera coleoptrata, the American house centipede, hatches with only 4 pairs of legs and in successive moults has 5, 7, 9, 11, 15, 15, 15 and 15 before becoming a sexually mature adult. Life stages with fewer than 15 pairs of legs are called larval stadia (~5 stages). After the full complement of legs is achieved, the now post-larval stadia (~5 stages) develop gonopods, sensory pores, more antennal segments, and more ocelli. All mature Lithobiomorph centipedes have 15 leg-bearing segments.
The Craterostigmomorpha only have one phase of anamorphis, with embryos having 12 pairs, and moultees 15.
The clade Epimorpha, consisting of orders Geophilomorpha and Scolopendromorpha, exhibits epimorphy: all pairs of legs are developed in the embryonic stages, and offspring do not develop more legs between moults. It is this clade that contains the longest centipedes; the maximum number of thoracic segments may also vary intra-specifically, often on a geographical basis; in most cases, females bear more legs than males. The number of leg-bearing segments varies widely, from 15 to 191, but the developmental mode of their creation means that they are always added in pairs — hence the total number of pairs is always odd.
Centipedes are a predominantly predatory taxon. They are generalist predators, which means that they have adapted to eat a variety of different available prey. Examination of centipede gut contents suggest that plant material is an unimportant part of their diet although centipedes have been observed to eat vegetable matter when starved during laboratory experiments.
Centipedes are mostly nocturnal. Studies on centipede activity rhythms confirm this, although there are a few observations of centipedes active during the day and one species Strigamia chinophila that is diurnal. What centipedes actually eat is not well known because of their cryptic lifestyle and thorough mastication of food. Laboratory feeding trials support that they will feed as generalists, taking almost anything that is soft-bodied and in a reasonable size range. It has been suggested that earthworms provide the bulk of diets for Geophilomorphs, since Geophilomorphs burrow through the soil and earthworm bodies would be easily pierced by their venom claws. Observations suggest that Geophilomorphs cannot subdue earthworms larger than themselves, and so smaller earthworms may be a substantial proportion of their diet. Scolopendromorphs, given their size, are able to feed on vertebrates as well as invertebrates. They have been observed eating reptiles, amphibians, small mammals, bats and birds. Collembola may provide a large proportion of Lithiobiomorph diet. Little is known about Scutigeromorph or Craterostigmomorph diets. All centipedes are potential intraguild predators. Centipedes and spiders may frequently prey on one another.
Centipedes are eaten by a great many vertebrates and invertebrates, such as mongooses, mice, salamanders, beetles and snakes. They form an important item of diet for many species and the staple diet of some such as the African ant Amblyopone pluto, which feeds solely on geophilomorph centipedes, and the South African Cape black-headed snake Aparallactus capensis.
Centipedes are found in moist microhabitats. Water regulation is an important aspect of their ecology, since they lose water rapidly in dry conditions. Water loss is a result of centipedes lacking a waxy covering of their exoskeleton and excreting waste nitrogen as ammonia, which requires extra water. Centipedes deal with water loss through a variety of adaptations. Geophilomorphs lose water less rapidly than Lithobiomorphs even though they have a greater surface area to volume ratio. This may be explained by the fact that Geophilomorphs have a more heavily sclerotized pleural membrane. Spiracle shape, size and ability to constrict also have an influence on rate of water loss. In addition, it has been suggested that number and size of coxal pores may be variables affecting centipede water balance.
Centipedes live in many different habitat types—forest, savannah, prairie, and desert, to name a few. Some Geophilomorphs are adapted to littoral habitats, where they feed on barnacles. Species of all orders excluding Craterostigmomorpha have adapted to caves. Centipede densities have been recorded as high as 600/m and biomass as high as 500 mg/m wet weight. Small geophilomorphs attain highest densities, followed by small Lithobiomorphs. Large Lithobiomorphs attain densities of 20/m. One study of scolopendromorphs records Scolopendra morsitans in a Nigerian savannah at a density of 0.16/m and a biomass of 140 mg/m wet weight.
Hazards to humans 
Some species of centipede can be hazardous to humans because of their bite. Although a bite to an adult human is usually very painful and may cause severe swelling, chills, fever, and weakness, it is unlikely to be fatal. Bites can be dangerous to small children and those with allergies to bee stings. The bite of larger centipedes can induce anaphylactic shock in such people. Smaller centipedes usually do not puncture human skin.
Even nonvenomous centipedes are considered frightening by humans due to their dozens of legs moving at the same time and their tendency to dart swiftly out of the darkness towards one's feet. A 19th century Tibetan poet warned his fellow Buddhists that "if you enjoy frightening others, you will be reborn as a centipede."
Evolution The upper three groups form the paraphyletic Anamorpha.
The fossil record of centipedes extends back to, during the Late Silurian. They belong to the subphylum Myriapoda which includes Diplopoda, Symphyla, and Pauropoda. The oldest known fossil land animal, Pneumodesmus newmani, is a myriapod. Being among the earliest terrestrial animals, centipedes were one of the first to fill a fundamental niche as ground level generalist predators in detrital food webs. Today, centipedes are abundant and exist in many harsh habitats.
Within the myriapods, centipedes are believed to be the first of the extant classes to branch from the last common ancestor. There are five orders of centipedes: Craterostigmomorpha, Geophilomorpha, Lithobiomorpha, Scolopendromorpha, and Scutigeromorpha. These orders are united into the clade Chilopoda by the following synapomorphies:The first post-cephalic appendage is modified to venom claws.The embryonic cuticle on second maxilliped has an egg tooth.The trochanter–prefemur joint is fixed.There is a spiral ridge on the nucleus of the spermatozoon.
Chilopoda is then split into two clades: the Notostigmophora including the Scutigeromorpha and the Pleurostigmophora including the other four orders. The main difference is that the Notostigmomorpha have their spiracles located mid-dorsally. It was previously believed that Chilopoda was split into Anamorpha (Lithobiomorpha and Scutigeromorpha) and Epimorpha (Geophilomorpha and Scolopendromorpha), based on developmental modes, with the relationship of Craterostigmomorpha being uncertain. Recent phylogenetic analyses using combined molecular and morphological characters supports the previous phylogeny. Epimorpha still exists as a monophyletic group within the Pleurostigmophoraa, but Anamorpha is paraphyletic.
Geophilomorph centipedes have been used to argue for the developmental constraint of evolution: that the evolvability of a trait, the number of segments in the case of geophilomorph centipedes, was constrained by the mode of development. The geophilomorph centipedes have variable segment numbers within species, yet as with all centipedes they always have an odd number of pairs of legs. In this taxon, the number of segments ranges from 27 to 191 but is never an even number.
Orders and families 
Representatives of centipede ordersScutigera coleoptrata (Scutigeromorpha: Scutigeridae)Lithobius forficatus (Lithobiomorpha: Lithobiidae)Geophilus flavus (Geophilomorpha: Geophilidae)
The Scutigeromorpha are anamorphic, reaching 15 leg-bearing segments in length. They are very fast creatures, and able to withstand falling at great speed: they reach up to 15 body lengths per second when dropped, surviving the fall. They are the only centipede group to retain their original compound eyes, with which a crystalline layer analogous to that seen in chelicerates and insects can be observed. They also bear long and multi-segmented antennae. Adaptation to a burrowing lifestyle has led to the degeneration of compound eyes in other orders. This feature is of great use in phylogenetic analysis. The group is the sole extant representative of the Notostigmomorpha, defined by having a single spiracle opening at the posterior of each dorsal plate. The more derived groups bear a plurality of spiracular openings on their sides, and are termed the Pleurostigmomorpha. Some even have several unpaired spiracles that can be found along the mid-dorsal line and closer to their posterior section of tergites. There are three families: Psellioididae, Scutigeridae and Scutigerinidae.
The Lithobiomorpha represent the other main group of anamorphic centipedes; they also reach a mature length of 15 thoracic segments. This group has lost the compound eyes, and sometimes has no eyes altogether. Instead, its eyes have facets or groups of facets. Its spiracles are paired and can be found laterally. Every leg-bearing segment of this organism has a separate tergite. It also has relatively short antennae and legs. Two families are included, Henicopidae and Lithobiidae.
The Craterostigmomorpha are the least diverse centipede clade, comprising only two extant species, both in the genus Craterostigmus. Their geographic range is restricted to Tasmania and New Zealand. They have a distinct body plan; their anamorphosis comprises a single stage; they grow from 12 to 15 segments in their first moult. Their low diversity and intermediate position between the primitive Anamorphic centipedes and the derived Epimorpha has led to them being likened to the platypus. They represent the survivors of a once diverse clade. Maternal brooding unites Craterostigomomorpha with the Epimorpha into the clade Phylactometria. This trait is thought to be closely linked with the presence of sternal pores, which secrete sticky or noxious secretions, which mainly serve to repel predators and parasites. The presence of these pores on the Devonian Devonobius permits its inclusion in this clade, allowing its divergence to be dated to.
The Scolopendromorpha comprise 21 or more segments with the same number of paired legs. Their antennae have 17 or more segments. Their eyes have at least 4 facets on each side. The order comprises the three families Cryptopidae, Scolopendridae and Scolopocryptopidae.
The Geophilomorpha bear upwards of 27 leg-bearing segments. They are eyeless and blind, and bear spiracles on all leg-bearing segments—in contrast to other groups, which only bear them on their 3rd, 5th, 8th, 10th and 12th segments—a "mid-body break", accompanied by a change in tagmatic shape, occurring roughly at the interchange from odd to even segments. This group, at 1260 spp. the most diverse, also contains the largest and leggiest specimens at 29 or more pairs of legs. They also have 14–segmented antennae. The group includes four families: Mecistocephalidae, Neogeophilidade, Geophilidae and Linotaeniidae.