Certain species of beetles possess defensive toxins that can cause adverse reactions upon contact or ingestion. It is important to distinguish between “poisonous” and “venomous” in this context. Beetles are generally considered poisonous, meaning they are harmful if ingested or touched, rather than venomous, which implies the injection of toxins through a bite or sting. These chemical defenses serve as a deterrent against predators.
Identifying Beetles That Are Toxic
Some beetles are toxic to humans. Two prominent examples include blister beetles from the family Meloidea and certain rove beetles, particularly those in the genus Paederus.
Blister beetles vary widely in color and size, ranging from a tenth of an inch to nearly three inches long. They often have a distinctive appearance with a relatively small head and thorax, and their wing covers may not fully conceal their abdomens. When threatened or crushed, these beetles engage in a behavior known as reflex bleeding, exuding a yellowish fluid containing a potent chemical called cantharidin from their leg joints. This fluid can cause skin irritation and blistering.
Rove beetles, particularly Paederus species, are small, soft-bodied insects. They are often dark orange with a black head, front wings, and the tip of their abdomen. Their short, hardened front wings (elytra) are characteristic, leaving much of their abdomen exposed. Like blister beetles, Paederus rove beetles do not bite or sting but release a toxic substance called pederin when they are brushed against or crushed on the skin.
How Beetles Produce and Use Toxins
The toxins found in beetles primarily function as a defense mechanism against potential predators. The production of these toxins varies among species; some synthesize their own, while others acquire them from their diet.
Cantharidin, the toxin produced by blister beetles, is a vesicant that causes blisters to form on skin upon contact. If ingested, cantharidin can lead to more severe internal issues, including digestive distress, internal bleeding, and kidney damage. Blister beetles synthesize cantharidin, with female beetles often acquiring additional amounts from males during mating, which is then used to protect their eggs.
Pederin, the toxin associated with Paederus rove beetles, is a potent amide produced not by the beetle itself, but by symbiotic bacteria, specifically Pseudomonas species, residing within the female beetle. This toxin inhibits protein and DNA synthesis, which leads to the characteristic dermatitis observed upon exposure. When a rove beetle is crushed, its hemolymph containing pederin comes into contact with the skin.
Responding to Potential Exposure
Upon contact with a blister beetle or rove beetle, immediately and thoroughly wash the affected skin area with soap and water. It is important to avoid rubbing or crushing the beetle directly on the skin, as this can release more toxins and worsen the reaction.
After washing, monitor the area for any developing symptoms, such as redness, itching, burning, or blistering. For mild skin reactions, over-the-counter creams or cool compresses may offer some relief. If symptoms are severe, persistent, or if the toxin has entered the eyes or mouth, seeking medical attention is advisable. In cases where ingestion is suspected, immediate medical consultation or contacting a poison control center is recommended.