Secret Weapon Water is Bed Bugs’ Kryptonite: Stealthy Parasites Avoid Wet Surfaces

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Humans tend to fear bed bugs, and rightly so. The bloodsuckers are tough to get rid of once they’ve entered a home. But new research has, for the first time, identified one thing the bugs seem to fear — water and wet surfaces.

A UC Riverside study published in the Journal of Ethology details a previously undocumented fear in bed bugs: wet surfaces. UCR entomology professor and paper co-author Dong-Hwan Choe says the finding seems to make perfect sense based on the shape of a bed bug’s physique.

Bed bugs have extremely flat bodies and small respiratory openings called spiracles on their belly sides. “If they physically contact a body of water, they’ll get stuck to its surface, blocking their respiratory openings,” Choe said. “Due to its strong adhesive power, water could be very dangerous from a bed bug’s perspective. So, it’s not surprising to learn that they’re extremely averse to moisture.”

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Researchers in the Choe lab discovered this insight serendipitously. Normally, laboratory bed bug colonies are kept in vials. To feed the bed bugs, the researchers attach an artificial feeder on the top of the colony vials. The insects crawl up to the top and poke their mouth parts through the membrane to ingest the blood.

One day, the membrane that holds the blood was slightly torn, and the blood from the feeder started to wet some paper used in the colony vials for the bed bugs to cling onto.

“The leaked blood was slowly soaking the paper from the top of the vial. I thought the bed bugs would be happy to drink the blood from the paper,” Choe said. “But what I saw was very different. They were actively avoiding the part of paper that became wet with blood. They wouldn’t even walk near the wet areas.”

The researchers also wet the paper substrate in the vials with water, and the insects avoided this as well. These observations inspired further study.

When a postdoctoral researcher in Choe’s lab, Jorge Bustamante, designed some experiments, he had to use a special infrared camera with a magnifying lens. “It’s not easy to work with young, really small bed bugs. They’re maybe only 2 millimeters long or less,” Choe said.

Using video analysis software, Bustamante could track differences in color between the bugs and the background, allowing him to record and quantify the insects’ movements. He paid close attention to the speed and distances the bed bugs traveled to avoid wet surfaces and also examined the behavior with respect to gender and age.

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He found that all bed bugs — males, females, old and young alike — avoid wet surfaces. The bed bugs in the study also tended to flee from the water faster than they approached.

However, he also saw that smaller, younger bed bugs make a faster U-turn when they realize they’re approaching a wet surface, showing the younger insects are more sensitive to water and dampness.

Aside from the novelty of being the first to publish insights into this behavior in bed bugs, there could be some implications for treating infestations. Companies may want to pay close attention to this behavior when developing and testing water-based insecticide sprays, as the bugs will actively avoid wet surfaces created by the treatments, and possibly move to other areas of the infested property, at least temporarily.

“If the insecticides don’t kill the bed bugs right away, then they will leave the treated areas and disperse elsewhere,” Choe said.

In addition, there is a simple solution if a person suspects they may have bed bugs on them.

“Take a bath. It’ll solve the problem,” Choe said. “Of course, the bed bugs in the room or on the bed will require different approaches.”

Original Article: Behavioral response of bed Bugs (Hemiptera: Cimicidae) to wet surfaces; Journal of Ethology; DOI:10.1007/s10164-025-00880-6

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