Centipedes found in soil environments, such as gardens and under rocks, are often encountered by people working outdoors. While most soil centipedes are generally harmless due to their small size and defensive nature, they are technically venomous. Understanding the distinction between venom and poison is key to assessing the threat posed by these subterranean arthropods.
Clarifying the Risk: Venomous, Not Poisonous
The difference between a venomous and a poisonous organism lies in the method of toxin delivery. An animal is considered poisonous if its toxins are harmful when ingested or absorbed through touch. Centipedes are classified as venomous because they actively inject toxins into another organism through a specialized mechanism.
Centipedes use a pair of modified front legs called forcipules, which function like pincer-like appendages located just behind the head. These forcipules contain venom glands that deliver a complex cocktail of neurotoxins, proteins, and enzymes to subdue their prey. While this venom is effective for hunting small invertebrates, its relative weakness and small injected dose mean it poses a low risk to human physiology.
Identifying Common Soil Centipedes
The centipedes most commonly found when disturbing soil belong to the order Geophilomorpha, often referred to as earth centipedes. These arthropods are highly adapted to their subterranean lifestyle, preferring dark, damp habitats like leaf litter and deep soil. A distinguishing feature of these true soil centipedes is their slender, elongated, and worm-like body, which allows them to burrow easily.
Geophilomorphs are typically smaller and paler than other centipede species, often appearing yellowish or brownish. They possess a high and variable number of leg pairs, always an odd count, ranging from 27 to over 190 pairs, with one pair per segment. These soil-dwelling species are blind and rely on their sensitive antennae to navigate and hunt in the dark environment.
What to Expect from a Centipede Bite
A bite from a small soil centipede is primarily a defensive reaction and results in localized, temporary symptoms. The immediate sensation is often described as a sharp, painful sting, comparable to a bee sting, though the pain level can vary. This initial pain is quickly followed by mild swelling and redness at the two puncture marks left by the forcipules.
The venom from these smaller centipedes rarely causes systemic effects in humans, with symptoms typically limited to the bite site. Any discomfort, which may include a burning or itching sensation, usually resolves itself within a few hours, though localized pain may persist for a day or two. Systemic reactions like headache or nausea are extremely uncommon, especially with the small Geophilomorpha species.
Immediate First Aid and When to Seek Help
The first step after a centipede bite is to thoroughly clean the affected area with soap and water to prevent secondary infection. To help reduce the localized pain and swelling, apply a cold compress or ice pack to the site. Some sources suggest that applying heat, such as warm water immersion, may also help, as centipede venoms are thought to be heat-labile.
Over-the-counter pain relievers can be used for discomfort, and an antihistamine may help manage any itching or minor swelling. While most bites are benign, immediate medical attention is necessary if signs of a severe allergic reaction develop. These signs include difficulty breathing, facial or throat swelling, or widespread hives. Medical consultation is also recommended if the localized symptoms worsen, show signs of infection, or do not improve within 48 hours.