Centipedes and millipedes are common arthropods. These multi-legged creatures often cause concern due to their appearance and the misconception that they are dangerous. While both belong to the subphylum Myriapoda, they possess distinct characteristics and defense mechanisms. Understanding these differences helps assess their potential impact on humans.
Clarifying the Terms: Poison vs. Venom
The terms “poisonous” and “venomous” are often used interchangeably, but they describe different ways toxins are delivered. An organism is poisonous if its toxins cause harm when ingested, inhaled, or absorbed through passive contact, such as touching its skin. In contrast, a venomous organism actively delivers its toxins, typically through a bite, sting, or injection. Venom requires a wound to enter the body, while poison does not. Centipedes are venomous, injecting toxins, while millipedes are not venomous and primarily use irritating secretions as a defense.
Centipedes: Their Defensive Bites
Centipedes are predatory arthropods that use venom to subdue prey and defend themselves. They deliver this venom through pincer-like appendages called forcipules, which are modified front legs located behind their head. These forcipules pierce the skin and inject venom containing neurotoxins, enzymes, and proteins. The size of the centipede often correlates with bite intensity, with larger species delivering more venom and causing greater pain.
A centipede bite typically results in immediate localized pain, redness, and swelling. Some individuals may also experience minor bleeding, itching, burning sensations, or numbness. While centipede bites are generally not life-threatening to humans, severe systemic reactions like nausea, dizziness, headache, or an irregular pulse are possible, especially from larger species or in individuals with allergies. In rare instances, hardening of the skin or tissue death may occur.
For basic first aid, clean the bite area thoroughly with soap and water. Applying a cold compress or ice pack can help reduce pain and swelling. Immersing the wound in warm water may also alleviate discomfort, as centipede venoms are heat-sensitive. Over-the-counter pain relievers and antihistamines can manage pain and allergic reactions. If symptoms worsen, a severe allergic reaction occurs, or infection concerns arise, seek medical attention.
Millipedes: Their Chemical Defenses
Millipedes do not possess fangs or stingers and therefore do not bite or sting as a defense. Instead, when threatened, they secrete various defensive chemicals from specialized glands along their segmented bodies. These secretions can contain compounds such as quinones, phenols, hydrogen cyanide, and organic acids. The specific chemical composition varies by species.
These defensive fluids can irritate human skin, causing a burning sensation, redness, and itching. Contact with certain millipede secretions can also lead to temporary skin discoloration, often appearing as a brownish stain that can last for weeks or months. If secretions contact the eyes, they can cause immediate pain, tearing, conjunctivitis, or inflammation of the cornea. In rare cases, more severe eye irritation or temporary vision issues have been reported.
If contact occurs with millipede secretions, wash the affected area immediately and thoroughly with soap and water. For eye exposure, rinse with plenty of water for at least 20 minutes, followed by professional medical evaluation. While millipede secretions are generally not life-threatening, allergic reactions can occur in sensitive individuals.
Identifying Centipedes and Millipedes
Distinguishing between centipedes and millipedes helps understand their behavior and potential risk. Centipedes typically have flattened bodies with one pair of legs per segment; their legs extend outwards, contributing to fast, agile movement useful for hunting prey. Centipedes also possess long, thread-like antennae. They can range in size from a few millimeters to over 30 centimeters in some tropical species. When disturbed, centipedes tend to scurry away quickly.
Millipedes, in contrast, often have more rounded or cylindrical bodies with two pairs of legs on most segments. This gives them a denser appearance, with legs positioned underneath their bodies. Millipedes move much slower than centipedes and are not typically predatory, feeding instead on decaying organic matter. Their antennae are generally shorter and elbowed. When threatened, millipedes often curl into a tight coil or ball as a defensive posture.