Blood-sucking bed bugs grow thicker skin to resist insecticides

The common bed bug, Cimex lectularius L. David Lilly

Bed bugs have adapted to common pesticides by developing a thicker skin, scientists say. The global resurgence of the blood-sucking species in the last decade could be explained by this evolutionary response.

Bed bugs are found in cracks and crevices in and around beds, and crawl out at night to feed off human blood, not unlike a mosquito. As a result, some people can develop itchy red bumps on their skin less than half an hour after being bitten, which can last several days.

The good news is that bed bugs do not carry any diseases which could harm humans. The bad news is they are hard to get rid of, and their presence can be distressing. Common insecticides are becoming less and less effective.

This latest study, published in PLOS ONE by scientists from Sydney University, sought to understand how bed bugs became so resistant, in order to come up with more adequate strategies to control the population.

Thickened skin

For the purpose of this research, the scientists collected a number of Cimex Lectularius L,
the common bed bug and exposed them to a common pyrethroid insecticide, while measuring the time taken to kill them.

Examining the bed bugs' morphology, the scientists discovered a link between cuticle (or skin) thickness and time to knock-out, or insect death. "Bed bugs, like all insects, are covered by an exoskeleton called a cuticle," explains lead author David Lilly, a PhD candidate at the University of Sydney. "Using scanning electron microscopy, we were able to compare the thickness of cuticle taken from specimens of bed bugs resistant to insecticides and from those more easily killed by those same insecticides."

With his team, he observed significant differences between bugs knocked down at two hours, four hours, 11 hours and finally, those still unaffected at 24 hours. These 24 hours survivors appeared to have statistically significantly thicker cuticle, which scientists believe is a result of evolution to insecticide resistance. In other words, the thicker the cuticle, the hardest it was to get rid of the little blood-sucker.

These findings may explain why we often fail in controlling bed bug infestations. More research, based on these results, could lead to the development of more efficient insecticides. "If we understand the biological mechanisms bed bugs use to beat insecticides, we may be able to spot a chink in their armour that we can exploit with new strategies," concludes Lilly.

How do I know if I have bedbugs?

Because bed bugs are small creatures and only go out at night, they can be difficult to spot. They are oval-shaped, and very flat. They can be up to 5mm long. Their colour can vary between dark yellow, red or brown. According to NHS choices, you can suspect your house is infested if you see the following signs:

- unexplained skin rashes or skin bumps

- black spots or blood spots on your sheets: this could be bed bugs faeces or blood from the bed bugs that you may have squashed after rolling over in your sleep

- An unpleasant, musty scent in the room: adult bedbugs produce this odour when they are disturbed, you will be able to smell it if you have a large infestation

- Mottled shells that bedbugs may have shed

In doubt, contact you local council or pest control firm ( which must be a member of the British Pest Control Association). If you act quickly, you have more chance of getting read of the insects quickly. It takes about seven weeks before bedbugs are discovered in another room of a property, on average.