Who would have thought: the bed bug's arch-enemy is actually water

Bed bugs, long known as parasites notoriously difficult to eradicate, can make removing them from a room a draining task. However, a recent study from the University of California, Riverside (UCR) has revealed a fatal weakness: bed bugs are afraid of water.

The findings, published in the Journal of Ethology, show that moisture and wet surfaces trigger a rapid avoidance response in bed bugs. The discovery provides a new perspective for scientists and the pest-control industry in addressing infestations.

This fear is not without reason but stems from their own anatomy. Bed bugs have very flattened bodies with small breathing holes called spiracles along the sides of their abdomens.

“If they come into direct contact with a puddle, they will become trapped on the surface, which then blocks their respiratory openings,” said Professor Dong Hwan Choe, an entomologist at UC Riverside.

He added that strong water adhesion is highly dangerous for their safety. “Therefore it is not surprising that they strongly avoid moisture,” he remarked.

Interestingly, this vulnerability was revealed accidentally in Professor Choe’s laboratory. Researchers were feeding bed bugs using a device containing blood. When the membrane of the device ruptured and blood seeped onto the paper inside the container, the researchers expected the insects to approach the blood spill.

“But what I saw was very different. They actively avoided the wet areas of the paper stained by blood. They would not even walk near the damp areas,” Choe explained.

After retesting with plain water, the results remained the same: bed bugs continued to avoid.

Using infrared cameras and motion-tracking software, the research team observed all groups of bed bugs displaying avoidance behaviour.

However, nymphs—the young bed bugs—showed a stronger reaction. With a body length of only about 2 millimetres, the risk of becoming trapped in droplets is much greater for them, so their survival instinct drives them to turn away more quickly when moisture is detected.

The findings serve as a warning regarding the use of water-based insecticides. If the spray does not kill the insects immediately, the wet surfaces could cause bed bugs to flee to other drier areas, thereby dispersing within the home.

“If the insecticide does not kill bed bugs immediately, they will leave the treated area and disperse to other places,” cautioned Professor Choe.

Although bathing can be a quick solution to remove bed bugs clinging to the skin, handling mattresses and rooms still requires more sophisticated strategies. By understanding this water phobia, experts can now design smarter and more effective pest-control methods.