Rain Ruins Insects' Sex Lives

Ladybugs doin' it. Photo: Anton Lefterov. 

If Hollywood has taught us anything, it's that rain is an aphrodisiac for humans. How many times have you seen a guy win back a girl after running through a thunderstorm to tell her important things about his feelings? Precipitation seems to be one of the most reliable ingredients for fornication.

But if you're an insect, rain is not so much a mood-enhancer as it is a barrage of death droplets from the sky. "For an aphid, a raindrop is something like what a refrigerator would be like falling on us," said Jeremy McNeil, an entomologist at the University of Western Ontario. Though the idea of being squashed by heavy objects might have currency in some BDSM circles, bugs play it safe and either lose interest in sex before heavy rainfalls, or try to get it over with as quickly as possible.

It's been a longstanding assumption that certain animals can detect environmental changes preceding precipitation, but José Bento's lab at the University of São Paulo, in collaboration with McNeil's team in Ontario, are among the first to provide experimental evidence of the theory, which they published in PloS ONE yesterday.

The true armyworm moth, the curcurbit beetle, and the potato aphid were selected for the study. They were chosen for their diversity in morphology, mass, and behavior, in order to better substantiate the hypothesis that a reduced sex drive in the hours before a storm is a common phenomenon amongst insects of all orders.

Beetles taking advantage of normal pressure. Photo: Orangeaurochs.

When exposed to falling pressures, the male beetles were far more aloof to the sexy pheromones of the females, and would not seek out the ladies if they were at a distance. When placed physically closer to the females, the males would reluctantly mate, but neither gender would indulge in the romantic foreplay that usually accompanies insect love-making. The males would not caress the females with their antennae, and the females would not play hard to get. It was very much a “wham-bam-thank-you-ma'am” affair.

The moths exercised similar caution. Females reduced the amount of pheromones they emitted when pressures dropped, and males were less responsive to the scents wafting in their direction. Aphids lost their mojo when atmospheric pressures sank and when they rose, a distinction that McNeil suggests is caused by the aphids' relative vulnerability to breezes.

Barometric changes in any direction heralds windier weather, and aphids are far lighter than the moths and beetles (plus they can't fly). The fact that females release pheromones by doing a handstand on the edge of a leaf calls for extra caution in the wake of any fluctuation in pressure.

An aphid secreting fluid. Photo: Sanjay Acharya.

Exactly how these insects detect acute environmental changes is still up for debate. The researchers speculate that micro-receptors on the insects' cuticles might tip off each individual to incoming rain, or perhaps it's the varying size of their gut-bubbles. McNeil also pointed out that this particular study was limited to scent communication, only one of many methods bugs use to exchange information.

“It'd be interesting to see how other insects with different communications respond to weather—for instance, crickets, that communicate with sound,” he said.

For now, one thing is clear: if a storm is coming, insects won't be.