The abrupt onset of cold weather has produced swarms of harlequin lady beetles (Coccinellidae: Harmonia axyridis). This past weekend hundreds (maybe thousands) of them encompassed my house, entering through tiny spaces to colonize my room. Surprisingly, this species was the only ladybug species and the only insect to emerge in abundance. In their quest for warmth, the beetles hugged my walls, lights, and heater during the night, while peering out the windows towards sunlight during the day. After a brief few weeks of fall weather, it looks like the temperature will continue to plummet, and these festive ladybugs will have a final opportunity to overwinter inside homes.
For this photo I placed two of the beetles on a brilliantly-red maple leaf (Acer rubrum) to show some of the variability in color pattern. Although this species has a striking diversity of black masks on the pronotum and charismatic spots, it is unfortunately invasive in the New World. The harlequin ladybug was introduced from East Asia to North America as a biocontrol agent for herbivorous aphids and scale insects. Like most futile attempts at species introductions, harlequins have had a detrimental effect on native insect fauna. Along with another invasive species, the seven-spot ladybug (Coccinella septempunctata), they are effective at outcompeting native coccinellids. Through examining species records spanning over a century, research in 2016 found dramatic population declines in native ladybugs likely due to niche overlap, as well as the extirpation of four species. Another study demonstrated the presence of a parasitic microsporidian in harlequin ladybug hemolymph. While the invasive harlequins are unaffected, native ladybugs that consume harlequin ladybug eggs are susceptible to the parasite which is often fatal.
Photographed after capture under controlled conditions