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The blood-feasting insects seem more active in the summer, according to new sleep-killing research.

Is anybody in Philadelphia itching? That could be because their mattress is infested with bed bugs, which are showing signs of a huge population surge all over the city.

This disheartening news comes from epidemiologists at the University of Pennsylvania School of Medicine, who are engaged in a pilot program to discover more effective ways to stamp out urban bed bugs. The scientists were able to get a picture of how the blood-drinking pests are spreading by monitoring phone calls to Philadelphia's Department of Public Health. They found that from 2008 to 2011, nearly half of all reported pest infestations were for bed bugs. The number of known infestations during this time increased by 4.5 percent a month – an incredible 70 percent each year.

Then from September 2011 to June 2012, there was a period of frenzied feasting with residents phoning in 236 complaints of sleep-killing insects. These calls came from all over town, although the pests seem particularly concentrated in south Philadelphia. And in a major step forward to understanding the nature of the beast, the researchers noted seasonal patterns in the infestations – something that's never really been locked down before.

Here's how Penn Medicine explains it:

A new study from Penn Medicine epidemiologists that looked at four years of bed bug reports to the city of Philadelphia found that infestations have been increasing and were at their highest in August and lowest in February. The findings, published ahead of print on January 8 in the Journal of Medical Entomology, point to two possible peak times to strike and eliminate the bugs.

"There is surprisingly very little known about seasonal trends among bed bug populations," said Michael Z. Levy, PhD, assistant professor in the Center for Clinical Epidemiology and Biostatistics (CCEB), who mapped the bed bug hotspots in Philadelphia in an effort to find more effective ways to control them. "We found a steep and significant seasonal cycle in bed bug reporting, and suspect that bed bugs have different levels of mobility depending on the season, and that their population size may fluctuate throughout the year."

Exactly why infestations skyrocket in the late summer is a bit of a mystery. The researchers speculate it might have something to do with the bugs becoming more active in warm weather, developing their little bodies quicker and having lots of raunchy bug sex.

On a random note, in the winter of 2012 I asked the Smithsonian Institution about possible seasonal behaviors of bed bugs. The response that came back from Gary Hevel, a research collaborator for the entomology department, showed how little was still known at the time. Hevel wrote:

That is an interesting question. I doubt that this idea has been experimentally investigated, so we will have to attempt to use logic for an answer. Bedbugs can be transported by humans on their clothing, and more clothing in the winter might afford more opportunities for travel by bedbugs. But it would depend more, I believe, in the habits and care that people take. Clothing (even sweaters, jackets and coats) that are hung in a closet would be less useful in bedbug transportation as the same garments that are tossed on a couch, across a bed, or on the floor adjacent to sleeping areas. Bedbugs are thought of hiding in mattresses, but are also to be found in the wooden parts of the bed, and will even hide under adjacent nightstands and wall hangings, mostly framed photos and art. More clothes in the winter might give bedbugs more opportunities, but it depends on where that clothing has been (distant from beds, chairs and couches, in a closet, would be better than otherwise). Still in play, however, is the non-seasonality of bedbugs, as they have generally adapted to pests of warm mammals (houses or nests).

The Philadelphia study should be available today at Penn Medicine or, if you have a membership, in the fascinatingly titled Journal of Medical Entomology. Please note that the Pennsylvania team is a separate enterprise from this mad scientist, who is based in New York and allows hundreds of bed bugs to suck at once on his arm:

Top image: smuay / Shutterstock.com

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