Flea larvae quickly drown when exposed to free water. And when soil moisture rises above 20%, the larvae die within 24 hours. Water also dissolves the adult flea feces in the environment, which the larvae depend on for nutrition.
Flooding & Irrigation
Outdoors, flea larvae develop in shaded, moist areas. However, they’ll quickly drown in a flooded environment. Rainwater or irrigation water from sprinklers can kill larvae in poorly drained areas. In addition, the water will dissolve adult fecal blood, which the larvae need for food.
It’s thought that fleas are most abundant in summers with slightly above average rainfall. But, in summers with heavy rainfall, flea populations are at their lowest numbers.
Flea larvae can survive in a soil moisture between 1-20%. Mortality drastically increases once above 20% Fig 1. The larvae live within two centimeters of the soil’s surface. When soil moisture exceeds 10%, the ground becomes saturated and gas exchange gets blocked. As a result, the larvae move to the surface. As soil moisture increases beyond 20%, a film of water develops on the surface and the larvae drown.
Fig 1 Percent of flea larvae that survive after 24 hours (y-axis) in different increments of soil moisture (x-axis), in three soil compositions.
Flea larvae are sometimes raised in jars for research. On warm days, they can end up drowning from condensation accumulating on a jar’s glass surfaces.