Lady beetles, often called ladybugs, are generally not poisonous to humans or pets. However, the presence of the invasive Multicolored Asian Lady Beetle (Harmonia axyridis) complicates this reality. This species is the primary source of reported issues due to its stronger defensive mechanism and tendency to aggregate in large numbers near human dwellings during cooler months. While accidental ingestion by a person is rare, the beetle’s defense compounds can cause problems for pets and trigger allergic reactions in sensitive individuals.
Identifying the Potential Threat
The majority of toxicity concerns stem from the invasive Multicolored Asian Lady Beetle (Harmonia axyridis). To distinguish it from native species, observe the area behind the head, known as the pronotum. Native lady beetles often have a uniform pattern, while the invasive Asian Lady Beetle typically displays a distinctive black marking resembling an “M” or a “W” shape against a white background.
The invasive species shows wide variation in color, ranging from pale yellow to deep red, and can have zero to nineteen spots. Harmonia axyridis is also slightly larger and more oval-shaped than native lady beetles. They become a nuisance when seeking winter shelter, gathering in large clusters on the sunny sides of buildings and often entering homes in the fall.
The Source of the Defensive Reaction
The lady beetle’s defensive capacity relies on a process called reflex bleeding, activated when the insect feels threatened. During this process, the beetle exudes a yellowish, foul-smelling fluid, which is its blood or hemolymph, from the joints of its legs.
The hemolymph contains a concentrated mix of defensive compounds, primarily bitter-tasting alkaloids, that deter predators. For the Multicolored Asian Lady Beetle, the alkaloid harmonine contributes to the fluid’s unpalatability and toxicity. The beetle’s bright coloration serves as a warning, signaling that the insect is chemically defended.
Effects on Household Pets
Ingestion by pets, especially dogs consuming large clusters of beetles, represents the most serious risk. When consumed, the insects release defensive hemolymph that can cause significant irritation and even chemical burns to the mouth tissues. In rare cases, the sticky fluid causes beetles to adhere to the mucosal lining of the mouth, often requiring manual removal by a veterinarian.
Symptoms of ingestion include excessive drooling, refusal to eat, and lethargy, indicating oral discomfort. The alkaloids can also cause gastrointestinal upset, resulting in vomiting, diarrhea, or minor ulcers in the stomach and intestines. Pet owners should seek veterinary attention if their dog shows these signs after consuming a large number of beetles.
Effects on People
The risks posed by lady beetles to humans are generally low, involving contact or allergic reactions rather than severe poisoning. Handling or crushing a beetle releases the yellow hemolymph, which may temporarily stain the skin and cause minor dermal irritation. The primary health concern arises when large aggregations of the Multicolored Asian Lady Beetle enter homes, releasing allergens from their hemolymph, shed exoskeletons, and droppings.
Exposure to these airborne allergens can trigger allergic reactions in sensitive individuals, manifesting as sneezing, runny nose, itchy eyes, and coughing. People with pre-existing conditions like asthma may experience more severe bronchial reactions, including wheezing and shortness of breath. Accidental ingestion is extremely unlikely, and the bitterness of the defensive fluid would cause immediate rejection, preventing serious harm.