It’s fall in the South Carolina Lowcountry and we’ve been watching hurricane forecasts, hoping for cooler weather, and brushing away lovebugs.
Twice a year, in early spring and again in late August to September, these small flies emerge en masse, swarming over lawns and patios, and piling up on the windshields and radiator grills of moving cars.
Native to Central America, lovebugs (Plecia nearctica) were first recorded and described in the U.S. in 1940. Since then, they have spread rapidly throughout much of the Southeast. During outbreaks, which last several weeks, swarms in some areas may number in the millions.
True to their name, swarming lovebugs tend to move around as mated pairs, coupled end-to-end. The egg-laden female is the larger one of the pair, about a third of an inch long. The male is noticeably smaller, with bigger eyes. Both have long legs and velvety black bodies, aside from a bright orange patch behind the head.
When not swarming and mating, lovebugs live quiet and inconspicuous lives as tiny, wormlike larvae at the soil surface. There they feed on grass clippings, leaf litter, and other organic matter. Once fully grown, the larvae enter a pupal stage, during which they gradually morph into winged adults.
Favorable environmental conditions, including warm temperatures and heavy rains, help prompt their synchronous emergence.
Males emerge first from the soil and hover nearby, forming growing swarms as they wait for females. Competition is intense, with the biggest males claiming the best spots, closest to the ground.
For a female lovebug, there are few preliminaries to sex: once she crawls onto a grass stem or takes to the air, she’s quickly grasped by a male. Mating takes about twelve hours, but the two flies may stay attached for as long as three days.
That’s a lengthy time commitment in the life of a lovebug, given that adults live less than a week.
During the coupling period, the pair may feed on pollen and nectar. Eventually the female deposits several hundred eggs on the soil surface.
Studies have shown that lovebugs are attracted to formaldehyde and other volatile components in the exhaust fumes of vehicles. It’s not clear why, but possibly these substances resemble the odors of decomposing organic matter (larval food) at egg-laying sites.
Lovebugs are also drawn to light-colored surfaces, the heat of engines, and the vibrations of cars. Small wonder, then, that lovebugs can be major nuisances to motorists driving through thick swarms.
When lovebugs end up smashed on the front of a car, their bodily contents become acidic after 24 hours. Their presence can eventually cause damage to the painted surface unless it’s washed promptly, before being baked by the sun.
Although lovebugs can certainly be a nuisance, they don’t bite or sting, nor are they known to transmit disease. Larvae help recycle decomposing organic matter, and adults play an important role as pollinators.
And for biologists, lovebug behavior raises interesting evolutionary questions.
Although it doesn’t happen often, both males and females can mate more than once, and single males try to disrupt established pairs.
So probably the long coupling period that’s so striking in lovebugs functions as a form of mate-guarding. By sticking close to his mate — literally — a male protects his hard-won reproductive “investment” and makes it more likely that it’s his sperm, not another male’s, that fertilize her eggs.