An airborne invasion of ladybugs has turned Sewanee into a pointillist’s drunken joke. Our house has several thousand of them jostling on the southern wall, with a few hundred making their way through hidden cracks to the interior. As I type, they bombard the keyboard. Walking outside, I get them in my hair, down my shirt, into pockets.
A plague of coleoptera? That seems to be the general opinion in town, with calls for chemical weaponry not far behind. More on that later.
Who are these creatures? They are Harlequin ladybird beetles (Harmonia axyridis), also known as Asian ladybugs or multicolored lady beetles. They’re looking for shelter over the winter. Any crack will do. The more the merrier: they call to each other with chemical attractants, possibly because there is safety in numbers.
These insects were first brought from east Asia to America in an attempt to enlist them in our never-ending fight against aphids. So the legions of ladybugs banging against our walls are a testament to the foresight of the USDA and a witness to the prodigious numbers of aphids that, despite their new Asian foes, crowd like feedlot cows on twigs and flower stems.
If swarms of colored beetles were a rare occurrence, the military-industrial-wedding-complex would be charging big bucks for uplifting releases of these merry air-dancers. No such luck: these insects have crossed the cultural threshold that divides purty from plague. How to deal with them? Some companies make lures and traps, decoying the beetles with a mimic of their aggregation pheromones. I have no experience with these devices, but I suspect that they are only partly successful. Like a liquor store on the edge of a college town, you’ll grab some of the swarm, but many others will BYO and head straight to the party. Vacuums work well on smaller swarms and a mesh or nylon stocking placed inside the suction tube (trap it between tube sections) will keep the doomed beetles out of your bag. Or just wait and they’ll disperse or die on their own. Eventually.
But this is not just a story about Homo vacuumus. These beetles may quite literally have a silver lining. Their ecological success is partly due to their invulnerability to disease, a super-power conferred by their “hemolymph” (insect blood). The potency of this vital essence is easily confirmed: poke a beetle and see the defensive yellow ooze of blood emerge from chinks in their legs, staining your hand and releasing a powerful odor. Studies of the antimicrobial properties of the blood show that it contains a chemical, harmonine, that inhibits both TB and malaria. Knowing this, I pick the ladybugs out of my hair with new found respect and even a sense of hope that medical wonders may yet emerge from the entomological onslaught.
The weaponry story does not end here, though. These insects not only carry chemical defenses in their blood, they may also attack competitors with biological weapons. A microbe that lives peacefully on the harlequin ladybug appears to be lethal to native ladybugs. When these natives prey on the eggs of the harlequin ladybug, the microbe attacks and death follows.
In sum: we’re under attack from insects that are in violation of multiple international arms agreements. Enjoy the spectacle.