Ladybugs are often seen as charming, beneficial insects in gardens, recognized by their bright colors and spots. However, the presence of yellow and black varieties can raise questions about their safety, particularly regarding whether they are poisonous.
Are They Poisonous to Humans and Pets?
Yellow and black ladybugs, most commonly the Asian lady beetle (Harmonia axyridis), are not truly “poisonous” in the sense of being highly toxic or venomous. These beetles employ defense mechanisms that can cause mild reactions in humans and pets. If a person handles them, the beetles may secrete a yellowish, foul-smelling fluid from their leg joints, known as reflex bleeding, which can cause slight skin irritation. Bites from these beetles are rare but can feel like a minor pinprick, seldom leading to serious issues.
For pets, especially dogs and cats, ingesting Asian lady beetles can lead to mild gastrointestinal upset. Symptoms such as reduced appetite, vomiting, diarrhea (which may be bloody), and lethargy have been reported. The hemolymph, the insect’s blood, contains corrosive compounds that can cause chemical burns or ulceration in the mouth and gastrointestinal tract. While serious cases are uncommon, veterinary consultation is advisable if symptoms are severe or persistent, particularly if beetles become embedded in the pet’s mouth.
Their Natural Defenses
The perception of yellow and black ladybugs as potentially dangerous stems from their sophisticated natural defenses. Their vibrant yellow and black colors serve as a visual warning signal (aposematism), indicating to potential predators that the beetle is unpalatable. When disturbed, these ladybugs engage in reflex bleeding, releasing a bitter, foul-smelling, yellowish fluid called hemolymph from their leg joints.
This fluid contains various alkaloid compounds, such as harmonine and adaline, which are unappetizing to predators and can be mildly irritating. Ladybirds can produce at least 50 types of alkaloids as part of their chemical defense.
Identifying the Species Often in Question
The ladybug species most frequently associated with yellow and black coloration and concerns about toxicity is the Asian lady beetle (Harmonia axyridis). This beetle exhibits a wide range of color variations, from pale yellow to orange or red, and can have anywhere from zero to 22 black spots. A distinguishing feature of the Asian lady beetle is the presence of an ‘M’ or ‘W’ shaped black marking on the white area behind its head, known as the pronotum.
Asian lady beetles are typically larger than many native ladybug species, often measuring about 1/3 inch in length. They are known for congregating in large numbers on the sunny, southwest sides of buildings in the fall, seeking sheltered locations to overwinter. These beetles may release a chemical pheromone to attract others to the same overwintering site.