Spanish fly secretes a toxic compound called cantharidin as a defense mechanism. Cantharidin can cause mild to severe toxic effects upon ingestion or contact with human skin, leading to blistering. Symptoms may range from skin irritation to severe digestive and urinary tract issues.

Spanish fly employs a defense mechanism that involves secreting toxins from its body. This secretion, which can be harmful upon ingestion or contact, serves as both a deterrent to predators and a means of capturing prey. The intensity of the toxicity can range from mild irritation to severe reactions, differing among various animals. For instance, humans might experience blistering on the skin, while small mammals like cats and dogs could exhibit signs of poisoning after ingestion. Birds affected by the toxin may exhibit distress and discomfort as well.

Spanish fly, at the adult stage, may cause allergies in a small number of people upon contact. Allergic reactions can range from mild to severe, manifesting typically as skin-related symptoms. The severity of an allergic response varies among individuals, so those who are allergic should handle spanish fly with caution to prevent potential adverse reactions.