Millipedes are common arthropods characterized by a segmented body and two pairs of legs on most segments. They are often found in moist, dark environments and are generally harmless. Many species, especially brightly colored red varieties, possess a chemical defense mechanism. Millipedes are not venomous, meaning they do not bite or sting to inject toxins. Instead, they release a defensive secretion that is irritating and can be toxic if ingested, which raises concerns about their safety for humans and pets.
Are Millipedes Poisonous or Venomous?
The distinction between “poisonous” and “venomous” is based on the method of toxin delivery. Venomous organisms, such as snakes, actively inject toxins using specialized structures. Millipedes lack these mechanisms and are not venomous. They secrete a chemical toxin passively, which is why they are often called “poisonous.” The most accurate term is “defensive secretion,” released when the millipede is physically threatened or crushed. This secretion is purely for repelling predators and is released onto the body surface.
The Chemical Defense System
Millipede defensive secretions are complex chemical mixtures produced and stored in glands called ozopores, located along the sides of the body segments. When threatened, the millipede releases this liquid to deter predators. Bright coloration, such as red, serves as a warning signal (aposematism) indicating the presence of these noxious compounds.
The most common components are benzoquinones, which cause most visible human reactions. These compounds are highly irritating to the skin and mucous membranes and can cause temporary orange or brown discoloration. Benzoquinones are deterrents due to their caustic nature and staining ability.
Some millipede groups, particularly the order Polydesmida, also secrete trace amounts of hydrogen cyanide (HCN). While HCN is highly toxic in large quantities, the small amount emitted by a single millipede is generally not enough to poison a human. Other components, including phenols and hydroquinones, contribute to the irritating effect. The primary toxicity risk, especially for pets, comes from ingesting these compounds, which can cause gastrointestinal distress.
Managing Exposure and Skin Irritation
Contact with millipede defensive fluid typically results in localized symptoms in humans that resolve quickly. Common reactions include a burning sensation, localized redness, and temporary skin discoloration caused by benzoquinones. If the fluid contacts the eyes, irritation and pain can be significantly more severe, requiring immediate attention.
Immediate first aid for skin exposure is to thoroughly wash the affected area with soap and water. This removes the oily secretions and limits the duration of staining and burning. If the fluid gets into the eyes, they must be rinsed continuously with copious amounts of water for at least 15 to 20 minutes.
Pets, especially dogs, may attempt to mouth or ingest a millipede, triggering the release of defensive fluid. The primary risk for pets is gastrointestinal upset, drooling, or distress due to the acrid taste and irritation. While ingestion rarely causes serious medical consequences, the chemicals can induce vomiting. If a pet ingests a millipede, monitor for persistent vomiting, lethargy, or severe oral irritation. Consult a veterinarian if symptoms are severe or do not resolve quickly. Prevention is the best management, which includes avoiding bare-handed contact and discouraging pets from eating them.