Centipedes are a class of ancient, predatory arthropods belonging to the subphylum Myriapoda, which also includes millipedes, symphylans, and pauropods. Centipedes have successfully colonized terrestrial environments worldwide, with a history stretching back over 400 million years. The exact number of centipede types remains an active question for scientists who continue to uncover new species in remote habitats.
Defining Characteristics of Centipedes
Centipedes are classified under the class Chilopoda, distinguishing them from their relatives like millipedes, which belong to the class Diplopoda. A fundamental characteristic of all centipedes is that each body segment bears only a single pair of legs. This feature is a clear contrast to millipedes, where most segments appear to have two pairs of legs due to the fusion of two segments during evolution.
Centipedes are active carnivores, and their predatory nature is defined by a unique anatomical feature called the forcipules. These pincer-like appendages, sometimes referred to as venom claws, are actually a modified first pair of legs. The forcipules are located directly behind the head and are used to grasp prey and inject venom to quickly subdue it.
Centipedes have a pair of antennae used for sensing the environment. Although the common name suggests one hundred feet, the actual number of legs varies significantly among species. Centipedes always have an odd number of leg pairs, ranging from a minimum of 15 pairs to a maximum of 191 pairs.
The Scale of Centipede Diversity
Determining the precise number of centipede species is a complex task due to their secretive nature and the challenges of taxonomy. Currently, scientists have formally described and cataloged approximately 3,000 to 3,500 centipede species globally. These described species are distributed across nearly every terrestrial habitat, from tropical forests to arid deserts.
The official count is widely considered an underestimate. Based on the rate of new discoveries and the exploration of remote ecosystems, the actual number of species is estimated to be much higher, potentially encompassing 8,000 or more species worldwide.
The discrepancy between the described and estimated number is largely due to the difficulty in studying these animals. Many centipedes live in microhabitats like deep soil, under rocks, or within rotting logs, making them hard to find and collect. Furthermore, many species look very similar, and distinguishing between them often requires detailed microscopic or genetic analysis, slowing the process of formal classification.
The Five Recognized Orders
Centipedes are organized into five universally accepted taxonomic Orders within the class Chilopoda. These orders represent distinct evolutionary lineages, each with unique body plans, life cycles, and ecological adaptations: Scutigeromorpha, Lithobiomorpha, Craterostigmomorpha, Scolopendromorpha, and Geophilomorpha.
Scutigeromorpha
The Scutigeromorpha order, commonly known as house centipedes, is instantly recognizable by its long, delicate legs and high agility. Adults in this group possess 15 pairs of legs, with the posterior legs being noticeably longer than the anterior ones. They are the only order to retain true compound eyes, giving them a unique form of faceted vision compared to other centipedes.
The respiratory system of this order is also unique, with spiracles—the external respiratory openings—located along the midline of the back, unlike the side-located spiracles of all other orders. This order is relatively small, with around 80 to 96 described species, and is often found in temperate and tropical regions.
Lithobiomorpha
Known as stone centipedes, the Lithobiomorpha order is characterized by a relatively short, compact body structure. Like the house centipedes, they have a fixed number of 15 pairs of legs once they reach maturity. They exhibit anamorphic development, meaning the young hatch with fewer legs and segments and gain the adult complement through successive molts.
These centipedes typically range from 4 to 40 millimeters in length and are commonly found in temperate zones under stones, bark, or leaf litter. Most species possess simple eyes, or ocelli, which are grouped in small clusters on the sides of the head, though some cave-dwelling forms are completely blind.
Craterostigmomorpha
The Craterostigmomorpha order is the least diverse of the five, containing only a single genus with two known species, making it the most geographically restricted group. Both species, Craterostigmus tasmanianus and Craterostigmus crabilli, are found exclusively in Tasmania and New Zealand.
These centipedes are morphologically intermediate between the Lithobiomorpha and the larger Scolopendromorpha. They have 15 pairs of legs, but their development is unusual, involving only a single stage of anamorphosis where they grow from 12 to 15 leg-bearing segments in one molt. They possess a single ocellus on each side of the head and can grow up to 50 millimeters in length.
Scolopendromorpha
The Scolopendromorpha order, often called tropical or bark centipedes, includes the largest and most robust centipede species in the world. Species in this group are epimorphic, meaning they hatch from the egg with the full adult number of leg-bearing segments. Most species have 21 pairs of legs, though some possess 23 pairs.
The Amazonian giant centipede, Scolopendra gigantea, is the largest known species, reaching lengths of up to 30 centimeters. This order is highly predatory and is most diverse in tropical and subtropical regions worldwide. While many species have four simple eyes (ocelli) on each side of the head, several families within the order are completely blind.
Geophilomorpha
Geophilomorpha, the soil or earth centipedes, represents the largest order in terms of described species, with around 1,100 known. These centipedes are highly adapted for a burrowing lifestyle, possessing long, very slender, and worm-like bodies.
This order is unique for having a variable and high number of leg pairs, which can range from 27 pairs to a maximum of 191 pairs. Geophilomorphs are entirely eyeless, relying instead on their sensitive antennae to navigate and hunt in the dark soil and leaf litter. They exhibit epimorphic development, hatching with their full complement of segments.