Centipede

Centipedes are venomous hunters that belong to the class Chilopoda, a group within the subphylum Myriapoda that also contains millipedes and other many-legged creatures. Their bodies are long and divided into segments, with each segment carrying a single pair of legs. Every centipede is venomous, and they deliver their venom through specialized front limbs called forcipules—these are actually modified legs that work like pincers, not fangs. Despite the common name, no centipede species ever has exactly 100 legs; instead, the number of leg pairs is always odd and ranges from 15 to 191. They are sometimes called "forty-legs" or "hundred-legs."

These animals are generalist carnivores, preying on whatever they can overpower. They live in a wide variety of terrestrial habitats, from tropical rainforests to deserts, but always need a moist microhabitat because they lack the waxy cuticle that helps insects and arachnids retain water. As a result, they avoid direct sunlight by staying hidden or being active at night.

The head is rounded or flattened, with a pair of antennae at the front. It also has two pairs of maxillae and a pair of elongated mandibles. The first pair of maxillae form the lower lip and have short palps. The first pair of limbs stretch forward over the mouth; these are the forcipules, which end in sharp claws and contain venom glands used to kill or paralyze prey. Centipede size ranges from just a few millimeters in smaller lithobiomorphs and geophilomorphs to about 30 centimeters in the largest scolopendromorphs.

Many centipedes lack eyes entirely. Others have a variable number of simple eyes (ocelli), sometimes clustered into what looks like compound eyes, but these can only tell light from dark—they provide no true vision. In some species, the first pair of legs act as sensory organs, pointing backward instead of forward like typical antennae. Some centipedes also have an unusual sensory structure called the organ of Tömösváry, located at the base of the antennae. It consists of a disc with a central pore surrounded by sensitive cells and likely detects vibrations, possibly giving a weak sense of hearing.

Forcipules are unique to centipedes. They are modified from the first pair of legs (maxillipeds) and form pincer-like appendages just behind the head. Though not mouthparts, they are used to grab prey and inject venom. Venom glands run through tubes from inside the head to the tip of each forcipule.

Behind the head, the body has at least fifteen segments. Most segments bear one pair of legs, but the maxillipeds project forward from the first body segment, and the last two segments are small and legless. Each pair of legs is slightly longer than the one in front, preventing them from overlapping and reducing the chance of tripping. The last pair of walking legs can be twice as long as the first. The final segment, called the telson, contains the openings of the reproductive organs.

Centipedes mainly use their antennae to find prey. Their digestive tract is a simple tube with digestive glands attached to the mouthparts. Like insects, they breathe through a tracheal system, usually with a pair of openings (spiracles) on each body segment. These spiracles lead to long tracheae and tracheoles that carry oxygen to the organs, except in Scutigeromorpha, where spiracles are unpaired and tracheae are short, and oxygen is carried by the respiratory pigment hemocyanin. Some centipedes can close their spiracles, and a few in dry environments have evolved a waterproof cuticle. They excrete waste through a single pair of malpighian tubules.

The back legs are also modified, into what are called ultimate legs (also known as anal, caudal, or terminal legs). Their use varies by species, but they are not used for walking. They may be elongated, thickened, or pincer-like, and are often different between males and females, possibly playing a role in mating. Because they have more glandular pores than walking legs, they may also serve a sensory function. Some centipedes use them for defense, to capture prey, to suspend themselves from branches, or to grab other centipedes. Members of the genus *Alipes* can stridulate their leaf-like ultimate legs to distract or threaten predators, and *Rhysida immarginata togoensis* makes a faint creaking sound by swinging its ultimate legs.

Centipedes and millipedes are both myriapods with long, multi-segmented bodies, many legs, a single pair of antennae, and postantennal organs. The key difference is that centipedes have one pair of legs per body segment, while millipedes have two. Their heads also differ: millipedes have short, elbowed antennae, a pair of robust mandibles, and a single pair of maxillae.