Centipedes

Centipedes are arthropods familiar to most people, and it is usually an unpleasant familiarity. During rainy seasons they will invade indoor habitats hiding in bedding and clothing. Exposure in the United States typically occurs July through September. They are nocturnally active, fast moving, and aggressive. Despite their name implying one hundred feet (centi, one hundred, ped, foot), no centipedes have this exact number of appendages.

Like many other arthropods, but unlike insects, centipedes bear a head and a long trunk with many leg-bearing segments. Centipedes possess one pair of legs per segment which allows to easily distinguish them from the superficially similar millipedes. Another feature that distinguishes them from millipedes is the presence of forcipules, the modified first segment upon which the head rests. This segment has pincerlike fangs with poison ducts. The head bears a pair of antennae, and simple light receptors called ocelli. Most centipedes attain the length of 1-2 inches, but the tropical Scolopendra gigantea may be 1 foot long. Centipedes do not have waxy waterproofing layer on their cuticle, hence, they lose water at low humidity levels. They avoid dissication by seeking moist habitats.

There are about 3,000 known species of centipedes, but few have individual common names. Scientists have divided the various centipede species into five orders: Scolopendromorphs (millipedelike forms); Lithobiomorphs (living-under-stone morphs); Geophilimorphs (earth-liking forms); Scutigeromorphs (shield-covered forms); and Craterostigmomorphs (species occurring only in Australia). The first two orders include species having fewer than 24 pairs of legs. Geophilimorphs are wormlike centipedes that are adapted to burrowing in the soil. Their leg numbers vary from 31 to 177 pairs. Geophilimorphs emit noxious chemicals when threatened.

Most centipedes are predators feeding on small arthropods, including other centipedes, snails, earthworms, and nematodes, but even toads and snakes are consumed by large species. Some may occasionally ingest leaf litter which can be seen in their guts. They detect their prey using antennae and legs. In daytime centipedes hide under loose bark, stones, leaves, and plant debris. All have venom glands opening into their jaws, and a bite of even a small centipede can be painful. They can also pinch with their last pair of legs. Though painful, the bite of centipedes is not lethal to humans, resembling the pain associated with a wasp sting 3,4.

Females of some species lay single eggs into holes in the soil, often coating them with a liquid that kills fungal spores. They then cover the eggs with soil before abandoning them. However, some female centipedes dig a small chamber in the ground, usually under a stone, and deposit a small cluster of eggs. They wraps themselves tightly around the eggs and occasionally lick them to clean 8. The young develop to adulthood slowly, taking several molts.

Their hunting/eating apparatus is quite formidable and includes two mandibles (jaws), teeth, and a pair of poison-injecting fangs. The legs are tipped with sharp claws that are capable of penetrating skin, and toxin produced at the attachement of each leg may drop into these wounds, causing inflammation, swelling, and itching 7.

Hemiscolopendra marginata, a Scocopendra species, Centipede with blue antennas

Hemiscolopendra marginata


The maxillipeds (poison claws or fangs) are modified legs used to inject venom and to dig or move soil. A poison gland is found within the base of the claw. The fangs are operated by powerful muscles that ensure that the fangs are not only driven into the victim but that the glands are simultaneously compressed and caused to squeeze out the venom 4.

Close-up picture of Hemiscolopendra marginata, a Scolopendra species, Centipede with blue antennas

Hemiscolopendra marginata

Centipede venoms, like snake venoms, are a complex mixture which contains esterase, proteinases, histamine, cytolysin, 5-hydroxytryptamine, lipids, and polysaccharides. A cardiotoxic protein from Scolopendra subspinipes, found in tropical and subtropical areas of eastern Asia as well as Hawaii, can induce high blood pressure in cats 6. This reddish brown species grows to about 9 inches long and has 21 pairs of legs.

In most cases, systemic toxicosis is not seen, but local tissue necrosis may occur. Signs generally subside within 48 hours. In some people complications from centipede envenomation may include a type II hypersensitivity reaction (immune complex deposition) causing recurrent swelling and itching several weeks after envenomation 8.

Scolopendra Video

Microscope photography and video © Larysa Johnston

References

  1. Maurice Burton, Robert Burton.International Wildlife Encyclopedia
  2. Herbert W. Levi, Lorna R. Levi, Herbert Spencer Zim. Spiders and Their Kin
  3. John L. Capinera.Encyclopedia of Entomology
  4. David C. Coleman, D. A. Crossley, Paul F. Hendrix. Fundamentals of Soil Ecology
  5. Thomas Eisner, Maria Eisner, Melody Siegler. Secret Weapons
  6. Andrew Wallace Hayes. Principles And Methods of Toxicology
  7. Ramesh Chandra Gupta. Veterinary Toxicology: Basic and Clinical Principles
  8. Donald G. Barceloux.Medical Toxicology of Natural Substances
  9. Marshall Cavendish Corporation. Insects and Spiders of the World: Volume 3
  10. Susan Scott, Craig Thomas. Pests of Paradise: First Aid and Medical Treatment of Injuries

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