for National Geographic News
"Sleep tight, don't let the bedbugs bite." This old saying may be becoming newly relevant. Bedbugs, which feast on human blood at night, are biting back in developed countries around the world.
The current invasion of North America, Australia, and Western Europe is highlighted in a new study published by the Institute of Biology, London. But it's still unclear why the parasites are returning to cities where they were exterminated some 50 years ago.
"The trend is very worrying," said the report's author, Clive Boase. Boase runs the Pest Management Consultancy in Haverhill, England. "Since the mid-1990s, numbers of reported infestations have almost doubled annually."
In parts of London bedbug infestations have risen tenfold since 1996, Boase says. In the U.S. the National Pest Management Association reports a 500 percent increase in bedbug numbers in the last few years.
Similarly, in Australia, there were as much as 700 percent more calls to pest-control companies in the four-year period ending in 2004, compared with the previous four-year period, according to the Institute of Clinical Pathology and Medical Research (ICPMR) in New South Wales.
The bug's dramatic comeback is perplexing, Boase says. The rebound comes even as other creepy crawlies, such as cockroaches and ants, are in retreat from people's homes. Boase says possible factors fueling bedbugs' global spread include growth in international travel, increased resistance to certain insecticides, and the introduction of new pest-control methods that leave bedbugs unharmed. Yet, he says, the precise cause or causes of the problem are yet to be determined.
In the 1930s the U.K. Ministry of Health stated, "In many areas all the houses are to a greater or lesser degree infested with bedbugs." But infestations quickly receded once synthetic pesticides such as DDT were introduced following World War II. By the 1980s bedbugs were almost nonexistent in Britain, the U.S., and many other developed countries.
No bigger than an apple seed, the bedbug is descended from plant-feeding insects that evolved skin-piercing mouthparts for sucking up blood. They are thought to have first gotten a taste for human blood when cave-dwelling humans lived beneath bug-infested bat roosts
Bedbugs are notoriously difficult to locate. They hide in mattresses and furniture, under floorboards, and even inside electrical equipment, emerging to feed only when it's dark. Adults can survive up to a year without blood, allowing infestations to persist through periods when properties are vacant.
Side effects of bedbug bites include itchy body swellings. Boase says that in rare casesusually involving people living in povertysevere infestations may lead to severe blood loss, due to the volume of feeding by hundreds or even thousands of bedbugs.
While studies have shown that HIV can survive on bedbugs' mouthparts for up to an hour, the insects are not known to be vectors for disease.
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