Fleas aren’t attracted to water. They’ll drown in it. Homemade flea traps often use a lamp and a container of soapy water. The lamp’s light attracts fleas, not the water. The fleas land in the water and are killed.
Flea Traps & Water
Homemade flea traps commonly consist of a container of water placed beneath a lamp. The light attracts the fleas, causing them to jump and land in the water. Adult fleas are positively phototactic, meaning they’re attracted to sources of light. Adding a few drops of dish soap to the water reduces the surface tension. As a result, the fleas sink and drown.
Water is a Hazard for Fleas
Fleas die in water. They’ll drown within 24 hours when submerged. However, they can survive for days on the water’s surface. Fleas are covered in a wax-like substance that repels water. The waxy layer helps prevent water from entering the respiratory system.
Flea larvae are especially vulnerable to drowning. They’ll quickly die in a flooded environment. In poorly drained areas, small amounts of rainwater or sprinkler water kill larvae. The water also dissolves adult feces, which larvae need for food. In research labs, flea larvae can even drown from accumulated condensation on glass surfaces.
Outdoors, flea larvae live in the upper two centimeters of soil. They can’t survive if soil moisture exceeds 20%. At 10% soil moisture, the ground becomes saturated and gas exchange is blocked. So the larvae move to the surface. Beyond 20% soil moisture, a film of water develops on the ground’s surface and the larvae drown.
The term hygrotaxis defines an organism’s response to humidity or moisture. Flea larvae are positively hygrotactic, meaning they’re attracted to areas of high humidity. They’ll desiccate when relative humidity (RH) falls below 50%. The ideal RH occurs between 75% and 92%. Above 75% RH, flea larvae can uptake water from the air. This is why they’re attracted to moist air. Other life stage don’t show this attraction to humidity.