Diversity, geologic age, and habit
"Poison claws", coloration, and body form
What makes a centipede a centipede? and Modifications for speed
House centipedes, introducted species, and taxonomic characters
Notostigmophora contains one order, Scutigeromorpha
Pleurostigmophora contains the remaining orders
Lithobiomorpha, strong tergite heteronomy
Craterostigmomorpha, one family, one genus, and one species
Scolopendromorpha, the body form that most people envision when centipedes are mentioned
Geophilomorpha, burrowers, diversity of habitat, diversity of form
Centipedes and humans
The name, “centipede,” literally means “hundred feet,” and chilopods are commonly referred to as “hundred-leggers.” Unlike millipedes, this term is literally correct as some centipedes in the order Geophilomorpha do have over 100 legs, the most known being 382 (191 pairs) on Gonibregmatus plurimipes, occurring on the Fiji Islands in the Pacific Ocean. Centipede segments possess one pair or two legs that, except for the last pair, arise laterally, are clearly visible along the sides of the body, and function in locomotion. The ultimate or last legs extend backwards well behind the caudal extremity of the body and are not used for locomotion; they may be modified for sensory or defensive functions.
The Chilopoda is not as diverse and speciose a taxon as the Diplopoda. It comprises only five living orders with around 2,800 described species out of an estimated global fauna of approximately 8,000 species (Adis & Harvey 2000); by contrast, millipedes have over three times as many orders (16) and 10 times as many estimated species (80,000). The Chilopoda also is not as ancient a group, as its fossil history dates back to the late Silurian period of the Paleozoic era, ca. 410 million years ago (Shear 1992). Centipedes occur sporadically north of the Arctic Circle, inhabit all subarctic environments, and are abundant in xeric desert biotopes, where they are one of the most commonly recognized terrestrial invertebrates. They are exclusively carnivores, preying primarily on smaller arthropods, but large-bodied representatives of the order Scolopendromorpha are known to attack and feed on small mammals, snakes, frogs & toads, and birds. Four of the five orders contain agile, fast-moving forms that are adapted for speed; the exception is the Geophilomorpha, whose species move slowly and burrow in the substrate in a manner similar to earthworms, by elongating and contracting their bodies.
Centipedes are flexible, “opisthogoneate” arthropods (reproductive tracts open at the caudal end of the body) with two anatomical divisions, a head and trunk. Except for the order Scutigeromorpha, they are dorsoventrally (top-to-bottom) flattened, and all chilopods possess “poison claws” (also called “prehensors” or “forcipules”) beneath the head with which they bite prey and potential predators including other centipedes; these structures possess internal glands that secrete venom that is toxic to their prey. Biting and injecting venom is the primary method of defense, but centipedes also employ camouflage, “aposematic” (warning) coloration, and “autotomizing” appendages (dropping those grasped by predators and then outrunning them). A few species also produce defensive secretions, and larger ones appear to have glands in their legs, as merely walking on skin can produce inflamed puncture wounds. Centipedes exhibit two basic body forms and lack the great array of ornamentations that exist in the Diplopoda. Some species are uniformly brown or dark gray in color while others are yellow, orange, red, blue, green, violet, or black; still others possess transverse stripes along the caudal margins of the “tergites” (dorsal plates), and the Indian species, Scolopendra hardwicki, displays alternating orange/red and black tergites.
The principal autapomorphy (unique derived character) of the Chilopoda is the “poison claws,” which, though associated with the head, are not mouthparts and are actually appendages of the first segment. The centipedes that are adapted for speed encounter a difficulty, because any long, slender object that moves swiftly forward generates side-to-side undulations that counter this motion (like the swaying of a train), so centipedes have developed anatomical modifications that dampen or reduce the undulations. One of these is “tergite heteronomy,” with alternating short and long plates (well developed in the Lithobiomorpha, poorly developed in the Scolopendromorpha), which shortens the body, thereby reducing the undulations, while maintaining the same number of legs to propel the animal rapidly forward. The other is “tergal fusion,” shown by the Scutigeromorpha, which strengthens the body and makes it more rigid in the places where undulations develop. The coxae (basal articles) of the last legs in geophilomorphs and scolopendromorphs, and the last few legs in lithobiomorphs, possess variable numbers of “coxal pores” that lead to internal glands that are absent from scutigeromorphs. These glands are thought to function as osmoregulatory organs, excreting water under wet conditions and absorbing it in dry environments.
The class Chilopoda consists of 2 subclasses, 5 orders, and 23 families (see ensuing classification). Nine families occur in the US and Canada, but the number of genera and species is uncertain because the composition of the two most speciose orders, Lithobiomorpha and Geophilomorpha, is unknown as they have never been comprehensively investigated.
The currently accepted classification of the Chilopoda is shown below; subfamilies are provided for the Scolopendromorpha, where Dr. Shelley has more taxonomic experience. Taxa known or thought to occur in North America are marked with asterisks.
In the Scutigeromorpha, the long-legged and swift-moving European species, Scutigera coleoptrata, has been widely introduced into North America and is often encountered in houses in cool, moist places like drains, sinks, bathtubs, and cellars. Additionally, five nominal species have been proposed for forms in Texas and Arizona: S. linceci, homa, dorothea, phana, and buda. Würmli (1973) placed S. homa, dorothea, and phana in synonymy under S. linceci, but their statuses warrant further study because type specimens do not exist for most of these, particularly S. linceci, described by Wood (1867) from an unspecified site in Texas. If S. linceci is a valid species, a supportive neotype specimen is mandatory, so a thorough scientific investigation of these additional North American scutigeromorphs constitutes a worthy research project. Shelley (2002) surveyed the Scolopendromorpha across the continent and documented an indigenous fauna of eight genera and 21 species. North America is thus the only continent in which this order has been thoroughly studied, and the Scolopendromorpha is one of the few invertebrate orders to have been surveyed across it. Another European centipede, Cryptops hortensis, a small-bodied scolopendromorph, has been widely introduced and is now established in urban environments in the US and Canada, and five additional exogenous species (and one genus) have been encountered occasionally, particularly at ports. The higher taxa (families and orders) are distinguished primarily by the number of segments and legs, the lengths of the appendages, the presence or absence of segmental modifications, the profile and general body form, and the configuration of the head. Determinations of centipede genera and species are more difficult than in millipedes because they lack the all important gonopods and telopods found in chilognath Diplopoda. Many centipede genera and species are superficially similar such that only an experienced taxonomist can distinguish one from another. Taxonomically important characters include the spinulation of the legs, especially the last pair, the setation on the antennae, the position and arrangement of sulci or sutures on the tergites, and the size and configuration of the “coxosternal tooth plates,” which extend anteriorly between the bases of the prehensors.
The subclass Notostigmophora contains only one order, Scutigeromorpha, which contains three families, 16 genera, and around 80 described species out of an estimated global fauna of 100-150 species (Adis & Harvey 2000). Scutigeromorphs are relatively short-bodied centipedes in which the “spiracles” (openings to the trachea or respiratory system) are located middorsally. Adults possess 15 pairs of very long legs that become progressively longer caudally, and the antennae are very long and whip-like, consisting of two basal articles and a long flagellum with hundreds of very short articles. The head is hemispherical or “dome shaped” and possesses two compound eyes that differ from those of insects; the trunk is not dorsoventrally flattened, and while adults have 15 “sterna” (ventral plates), there are only seven large terga because of “tergal fusion.” Scutigeromorphs demonstrate “anamorphic” development (they hatch from the egg with less than the full adult complement of legs and segments, and add legs and segments, and grow larger, at subsequent molts until they reach this number) and hatch with only four segments and leg pairs. Scutigeromorphs are extremely fast, agile, and delicate centipedes that are difficult to catch and collect intact; the legs are readily autotomized, and few museum specimens possess all 15 pairs.
The remaining four orders, containing the vast majority of species, belong to the subclass Pleurostigmophora, which comprises dorsoventrally flattened centipedes in which the spiracles are located laterally and the appendages are not prolonged; eyes, when they exist, are simple ocelli on both sides of the head. Two orders, Lithobiomorpha and Craterostigmomorpha, demonstrate “anamorphic” development, while the Scolopendromorpha and Geophilomorpha are “epimorphic” (hatchlings emerge from the egg with the full adult complement of legs and segments and grow larger at subsequent molts). In the “epimorphic” orders, the eggs and early stadia are “brooded” by females, which curl or hump their bodies over the egg masses, whereas eggs are laid singly and not brooded in the Lithobiomorpha. According to Lewis (1981), brooding occurs in the anamorphic Craterostigmomorpha, but little is known about life history and development in this order.
The Lithobiomorpha comprise short-bodied forms with 15 pairs of legs and segments in adults, and 7 (rarely 6 or 8) in hatchlings. They exhibit strong tergite heteronomy, as tergites 1, 3, 5, 7, 8, 10, 12, and 14 are much longer than those of the other segments. Lithobiomorphs typically possess ocelli, but a few, mostly cavernicolous species, have lost them. The order occurs globally and comprises two families that are distinguished by the presence of setae alone on the legs (Henicopidae) or spines/spurs plus setae (Lithobiidae). There are 95 genera, and ca. 1,500 species have been described from an estimated global fauna of >2,000 species (Adis & Harvey 2000).
The Craterostigmomorpha is the most geographically restricted and least-diverse order. It occurs only in Tasmania (not Australia proper) and New Zealand, and was thought to be restricted to the South Island of the latter until Shelley (2002) cited it from the North Island based on a discovery by G. Edgecombe. The order comprises only one family, one genus, and one described species (Craterostigmus tasmanianus); there is at most only one other species, currently undescribed, as some specialists believe the form in New Zealand is specifically distinct. Craterostigmomorphs have 15 pairs of legs and sterna, but there appear to be 21 tergites (plus a terminal structure) because tergites 3, 5, 7, 8, 10, and 12 are subdivided. There is one pair of ocelli; the head capsule is longer than wide; and the “poison claws” extend well in front of the latter and are clearly visible in dorsal view (from above). The terminal structure is bizarre, as it consists of two valves that are fused dorsally but meet in a longitudinal slit ventrally; its function is unknown.
The order Scolopendromorpha contains the most readily recognized chilopods and is the body form that most people envision when centipedes are mentioned. Opinions differ as to the number of component families and their respective names, but the consensus seems to be three families – Scolopendridae, Scolopocryptopidae, and Cryptopidae – based in part on the presence (Scolopendridae) or absence (Scolopocryptopidae and Cryptopidae) of two pairs of ocelli on each side of the cephalic plate and the number of segments (21 in the Scolopendridae [except for Scolopendropsis, which has 23] and the Cryptopidae, and 23 in the Scolopocryptopidae). The last family is sometimes cited as “Newportiidae,” and both names were established by Pocock (1896), Scolopocryptopidae coming on p. 28 immediately before Newportiidae, on p. 29. Neither name has priority based on Pocock’s treatment, but Shelley (2002, pp. 2-3) noted that according to Article 24.2.2 of the present Code and the action of Attems (1930), as first reviser, Scolopocryptopidae has priority, and Newportiinae is thus one of three subfamilies; for these reasons, Scolopocryptopinae cannot be a subfamily under Newportiidae.
The final centipede order, Geophilomorpha, is unique in several ways. It is the only one whose species are not adapted for speed and instead burrow slowly in the substrate; it is the only order in which species reach the magic figure of 100 legs (the number in this order, always an odd number of pairs, ranging from 54 [27 pairs] to 382 [191 pairs]); and it is the only order with appreciable diversity, as there are currently 14 component families, 180 genera, and ca. 1,100 described species out of an estimated global fauna of around 4,000 species. Eyes are always absent, and the head is usually lenticular in shape, though it can be elongated and rectangular, as in the Mecistocephalidae. The last pair of legs typically lies along the longitudinal body axis; and the inflated coxae bear variable numbers of pores. Geophilomorphs vary greatly in size, from around 5 to 195 mm ( 0.2 to 7.8 in.) in length; some are thin and fragile while others are broad and ribbon-like. They occur natively on all the inhabited continents and some species have been introduced onto oceanic islands. They range from sea level to high elevations in the Andes and Himalaya Mountains, and several species have adapted to living in the littoral zones of sea-shores, a difficult environment to adapt to because of the high salinities.
As with millipedes, we close this general section by addressing the impact of chilopods on humans. All centipedes possess “poison claws” and can inject venom, but most are too small and weak to penetrate human skin. However, large and even moderate-size scolopendromorphs and scutigeromorphs, with their powerful “prehensors,” can inflict painful bites that may generate intense pain, swelling, discoloration, numbness, and necrosis, and necessitate a visit to a doctor. However, unlike scorpions and spiders, there are no really dangerous, deadly centipedes, and the only suspected instance of a human fatality is of a 7 year old child in the Philippines who was bitten on the head by a Scolopendra and the poison quickly entered the brain. Dr. Shelley was once bitten on a finger by a specimen of Scolopocryptops sexspinosus that was slightly over an inch long, and the digit swelled up and throbbed for about an hour, thus being similar to a wasp sting. In the southeastern US, Hemiscolopendra marginata, which can grow to 75 or so mm (3 in.) in length, frequently enters buildings, and persons accidentally encountering it can be bitten. During World War II, Scolopendra subspinipes was a scourge to American soldiers fighting in the Pacific. It is a wandering species, and large individuals roamed freely around military installations, falling into foxholes and entering latrine shelters and tents, where they would crawl into blankets on beds. Many soldiers were bitten and experienced instant, fiery pain; medical staff were frequently called to treat centipede bites, and an ingenious medic conceived of injecting localized dental anesthetics in the vicinities of bites, which afforded quick relief (Remington 1950). Thus, while there are no dangerous, deadly centipedes, the bite of large ones can cause severe pain and discomfort, to the point that persons living in tropical areas should be suitably cautious. Collectors should always pick up even moderate-sized species with forceps, never the hands, and because of the flexibility of their bodies, specimens should always be grasped behind the head so as to be able to control the biting end of the body. If they are grasped near mid-length or caudally, the animals can bend their bodies 180 degrees and still bite one’s hand or fingers.
Adis, J., & M. S. Harvey. 2000. How many Arachnida and Myriapoda are there world-wide and in Amazonia? Studies on Neotropical Fauna and Environment, 35:139-141.
Pocock, R. I. 1895-1910. Chilopoda and Diplopoda. Biologia Centrali-Americana, 217 pp. [Fascicles treating the Scolopendromorpha distributed in December 1895 and January 1896].
Wood, H. C. 1867. Descriptions of new species of Texan Myriapoda. Proceedings of the Academy of Natural Sciences of Philadelphia, 19:42-44.
Würmli, M. 1973. Die Scutigeromorpha (Chilopoda) von Costa Rica, Ueber Dendrothereua arborum Verhoeff, 1944. Studies on the Neotropical Fauna, 8:75-80.