Invertebrates
Asian Lady Beetle
Harmonia axyridis · also called multicolored Asian lady beetle, harlequin ladybird
Every autumn, homeowners across much of North America find their window frames and attic corners suddenly crowded with hundreds of orange beetles, an overwhelming success story for a species that was deliberately introduced decades earlier to solve a much smaller problem than the one it eventually created.
Overview
The Asian lady beetle, Harmonia axyridis, is a beetle now found across forest, grassland, and agricultural habitat throughout most of North America, having spread widely since its deliberate introduction for aphid control. Its remarkable colour variability, effectiveness as a pest predator, and tendency to swarm into buildings by the thousands each autumn make it one of the most consequential intentionally introduced insects on the continent.
A pest-control success that became its own problem
Introduced specifically to eat the aphids damaging North American crops, the Asian lady beetle did exactly that, and then went on to outcompete several native ladybird species and turn into an unwelcome autumn houseguest almost nobody anticipated.
Status
Not Evaluated and not of conservation concern itself, though considered an invasive species of concern in North America for its effects on native ladybird populations, with numbers and range still increasing.
Asian Lady Beetle: common questions
Why was the Asian lady beetle introduced to North America?
This species was deliberately released multiple times through the twentieth century specifically to help control aphids and other soft-bodied crop pests, since it is an effective natural predator of these pests, and the introductions were considered successful enough that the species is now widely established and common across most of the continent.
Why does the Asian lady beetle swarm into houses in autumn?
In autumn, large numbers of this species seek out sheltered spaces to survive the winter, and buildings with attics, wall voids, and window frames offer exactly the kind of protected, temperature-buffered spaces the species would otherwise seek out in rock crevices in its native range, leading to large indoor aggregations that can number in the thousands in some homes.
How can you tell an Asian lady beetle from a native ladybird?
This species shows an unusually wide range of colour and spot variation compared with most native ladybird species, ranging from pale orange to deep red with anywhere from no spots to nearly twenty, and it often has a small dark M or W-shaped marking just behind the head, though the sheer variability of its appearance can still make confident identification tricky without close comparison to reference images.
Is the Asian lady beetle harmful to native ladybirds?
Yes, to some degree, since this species has become so successful and abundant in parts of North America that it now outcompetes several native ladybird species for food and habitat, and it has also been documented preying on native ladybird eggs and larvae directly, contributing to documented declines in a few native species in areas where the Asian lady beetle has become especially common.