Harmonia Axyridis - Biology and Behavior

Biology and Behavior

H. axyridis hibernate in cooler months, though they will wake up and move around whenever the temperature reaches about 10 °C (50 °F). Because the beetles will use crevices and other cool, dry, confined spaces to hibernate, significant numbers may congregate inside walls if given a large enough opening.

These beetles use pheromones to "call" each other, allowing for the large gatherings that are often seen in the Autumn. This is exploited by the makers of H. axyridis traps.

They often congregate in sunlit areas because of the heat available, so even on fairly cold winter days, some of the hibernating beetles will "wake up" because of solar heating. These large populations can be problematic because they can form swarms and linger in an area for a long time. These beetles can form groups that tend to stay in upper corners of windows. This beetle has been also found to be attracted to dark screening material for its warmth. This beetle has good eyesight, and will come back from where it was removed, and is known to produce a small bite if provoked.

H. axyridis, like other lady beetles or ladybirds, uses isopropyl methoxy pyrazine as a defensive chemical to deter predation, but also contains this chemical in its hemolymph at much higher concentrations than many other such species. These insects will "reflex bleed" when agitated, releasing hemolymph from their legs. The liquid has a foul odor (similar to that of dead leaves) and can cause stains. Some people have allergic reactions, including allergic rhinoconjunctivitis when exposed to these beetles. Sometimes, the beetles will bite humans, presumably in an attempt to acquire salt, although many people feel a pricking sensation as a lady beetle walks across the skin. Bites normally do no more harm than cause irritation although a small number of people are allergic to bites.

These beetles can sometimes be difficult to identify because of the variations in color, spot size, and spot count of the elytra. The easiest way to identify H. axyridis is to look at the pronotum and see if the black markings look like a letter "W" or "M" (depending on if the marking is viewed from the front or the back). There is more white on the pronotum in this species than in most native North American species.