Bed bugs deterred by body hair: Study

By Dr. Ananya Mandal, MDDec 18 2011

According to Sheffield, UK researchers hairy skin may be the key to avoiding being bitten by bed bugs. The study was reported in the journal Biology Letters. Researchers say the hair slows down the bed bugs and warns the victim.

Pest controllers say the UK is currently experiencing a steep rise in the number of bed bug infestations. The bugs are about the size and color of a flat apple seed, and are found not only on mattresses and upholstery, but in suitcases, boxes, shoes, wallpaper and headboards.

Prof Michael Siva-Jothy, from Sheffield University's Department of Animal and Plant Sciences, recruited 29 brave volunteers to test the theory further, watching the bedbugs as they found a place to feed and removing them only as they were about to bite.

The results showed that more layers of both longer visible hairs and finer, “vellus” hairs near the surface appeared to work as a deterrent to the insects, with the finer hairs also acting as an early warning system. Prof Siva-Jothy said, “Our findings show that more body hairs mean better detection of parasites - the hairs have nerves attached to them and provide us with the ability to detect displacement.” He said they also slowed down the insect as it searched for a tasty spot to bite. “The results have implications for understanding why we look the way we do, what selective forces might have driven us to look the way we do, and may even provide insight for better understanding of how to reduce biting insects' impact on humans.”

He pointed out, “Men have more body hair than women which is caused by the action of testosterone at puberty. This does not necessarily mean that women are more likely to be bitten.” Professor Siva-Jothy suggested this pointed to an evolutionary battle between bed bugs and their prey, with the insects adapting to automatically head for relatively hairless bits of the body, such as wrists and ankles. He added that extreme hairiness might also be more of a disadvantage than an advantage. “If you have a heavy coat of long thick hairs it is easier for parasites to hide, even if you can detect them. Our proposal is that we retain the fine covering because it aids detection and if we lost all hair, even the relatively invisible fine hair, our detection ability goes right down.”

Prof Mark Pagel, an evolutionary biologist at the University of Reading, said that biting parasites remain a major cause of disease and death worldwide, making them a potentially enormous evolutionary pressure on early man. He said, “This vellus hair is certainly no use for anything else, so it is a reasonable hypothesis that it developed in response to a strong selective pressure in our past. Mammals are unique in developing this wonderful fur, and humans are the only mammals to jettison it, so there must have been a very good reason to do so.”

Catherine Hill, a medical entomologist at Purdue University, said it made sense that more hair would slow down foraging bedbugs. “But it’s a bit counterintuitive that the host has a greater number of bedbug detections when there’s more hair,” Hill said. “But in a way, it makes sense. Hair is like our antennae, and it initiates a response from us by sending signals to our nervous system.”

The Sheffield scientists are investigating the biology, reproduction and immunity of blood-sucking insects. Their aim is to find more effective ways of controlling parasitic insects and the diseases they spread.