Centipedes are predatory arthropods characterized by their elongated, segmented bodies and numerous legs, often causing concern when they appear indoors. The sight of these fast-moving creatures frequently leads to questions about their potential danger to humans. This concern often stems from confusion about whether the organism is passively toxic or actively injects a harmful substance. Understanding the biology of a small centipede is the first step toward accurately assessing the threat they pose to people and pets.
Clarifying the Difference Between Venomous and Poisonous
The terms “poisonous” and “venomous” are often used interchangeably, but they describe two distinct mechanisms of toxin delivery. An organism is defined as poisonous if its toxins are absorbed passively, such as through ingestion or touch. Harm occurs when the toxin is introduced into the body, typically by eating the organism.
In contrast, a creature is venomous when it actively injects its toxins into another animal using a specialized apparatus, like a fang or a stinger. Centipedes fall into the venomous category because they use modified front legs, known as forcipules or maxillipeds, to deliver their venom. These pincer-like structures are located just behind the head and contain glands that secrete a toxic cocktail designed to subdue prey. Centipedes do not possess passive toxins on their skin or tissue.
Identification of Common Small Centipedes
The small centipede most commonly encountered inside homes across North America is the house centipede, Scutigera coleoptrata. This species is relatively small compared to its tropical relatives, typically ranging from one to one and a half inches in body length. House centipedes are identified by their distinct yellowish-gray coloring, three dark stripes running down their back, and their long, delicate legs that allow for fast speed.
These centipedes are attracted to dark, damp environments, frequently making their home in basements, bathrooms, and crawl spaces where moisture is high. While they are venomous, the forcipules of Scutigera coleoptrata are usually too small and weak to effectively pierce human skin. Bites are rare and generally only occur if the centipede is handled or accidentally pressed against the skin. Even when a bite is successful, the small amount of venom injected is not considered medically significant to a healthy human adult.
Symptoms of a Bite and Immediate First Aid
When a small centipede bite occurs, the symptoms are typically localized and mild, often compared to the discomfort of a bee or wasp sting. The immediate reaction is usually a sharp, localized pain at the site of the dual puncture marks left by the forcipules. This pain is often followed by minor swelling and redness confined to the immediate area.
To manage a bite, clean the wound thoroughly with soap and water to prevent secondary bacterial infection. Applying a cold compress or an ice pack wrapped in a cloth can help reduce swelling and alleviate the burning sensation. Over-the-counter pain relievers such as acetaminophen or ibuprofen can manage discomfort, and an antihistamine may help reduce minor swelling and itching.
Watch for signs of a more severe reaction, though they are uncommon. If the pain intensifies significantly, the swelling spreads rapidly, or if systemic symptoms like difficulty breathing, dizziness, or widespread hives develop, seek immediate medical attention. In the vast majority of cases involving small centipedes, the symptoms resolve completely within a few hours to a day without professional medical intervention.
Keeping Centipedes Out of the Home
Centipedes enter homes because the indoor environment provides them with two primary needs: moisture and a reliable food source. Therefore, the most effective strategy for prevention is to eliminate these attractive conditions. Reducing humidity levels in damp areas like basements and crawl spaces is primary, often accomplished by using dehumidifiers or ensuring proper ventilation.
Sealing potential entry points is a physical barrier that limits access to the home’s interior. Applying caulk to close cracks in the foundation, around utility pipes, and along windows and door frames prevents centipedes from slipping inside. Outside the home, removing potential hiding spots like piles of leaf litter, wood stacks, and excessive mulch close to the foundation will discourage them from approaching the structure. Controlling the population of other household pests, such as spiders and insects, removes the centipede’s food supply, making the home an undesirable place to hunt.