The idea that bats are the ultimate natural defense against mosquitoes is a widespread belief, often leading people to install bat houses expecting to eliminate backyard pests. To determine the actual impact bats have on mosquito populations, it is helpful to examine the scientific evidence regarding their feeding habits and ecological role. Understanding the reality of a bat’s diet clarifies their pest management contribution and informs efforts to support these nocturnal insectivores.
The Reality of Bat Diets and Mosquito Consumption
Insectivorous bats, particularly the microbats common in North America, are generally opportunistic feeders that consume a wide variety of arthropods. Analysis of bat guano confirms that their diet is not specialized to target mosquitoes alone. Larger insects like moths, beetles, and caddisflies often form the bulk of the biomass consumed. These larger prey items offer a more substantial caloric reward for the energy expended during the hunt.
Mosquitoes, which are very small, represent a minor percentage of a bat’s total dietary volume and energy intake, even though they are frequently consumed. Some smaller species, such as the little brown bat (Myotis lucifugus), do show a high incidence of mosquitoes in their diet. Modern studies using DNA metabarcoding of guano samples have confirmed that little brown bats frequently consume mosquitoes, with one study detecting them in over 70% of samples. This suggests that while mosquitoes are certainly prey, they are not the primary food source in terms of total mass, especially for larger bat species for whom a mosquito provides insufficient calories.
The foraging strategy of bats is based on the profitability and detectability of prey, and they are not specifically adapted to be specialist mosquito hunters. Larger bats, such as the big brown bat (Eptesicus fuscus), tend to favor hard-bodied insects like beetles. Even these larger bats have been shown to consume mosquitoes, though less frequently than their smaller counterparts. The ecological role of bats is better understood as generalized insect population regulation rather than targeted mosquito control.
The Magnitude of Insect Control
While mosquitoes may not be the primary focus of a bat’s diet, the sheer volume of insects consumed nightly translates to a substantial ecological service. A single insectivorous bat can consume hundreds to over a thousand insects in an hour, or several thousand throughout the night. A nursing mother bat may consume a quantity of insects equivalent to her own body weight every night to support lactation.
Maternity colonies, which can number in the hundreds or thousands, result in enormous collective consumption of insects over a summer season. This high volume of predation provides significant generalized pest control, particularly against agricultural pests like moths and beetles. The economic benefit of this natural pest suppression has been estimated to be in the billions of dollars annually.
The insects consumed include those that are larger and often more damaging to crops or disruptive to human environments, such as cutworm moths and cucumber beetles. Even though mosquitoes are a small fraction of the diet, the consistent removal of thousands of insects per night contributes to a reduction in overall insect pressure. Bats function as generalized population regulators, helping to stabilize insect populations and supporting a healthier local ecosystem.
Considerations for Attracting Bats to Your Property
For those interested in attracting bats for generalized insect control, installing a bat house that meets specific criteria is the most effective approach. Bats seek a roost that provides high, stable temperatures, especially for raising young in maternity colonies. The house design should incorporate multiple chambers, typically three or four, separated by narrow roosting spaces of approximately 3/4 to 1 inch wide.
The house construction requires specific features to ensure occupancy:
- The interior wood surfaces must be roughened horizontally with grooves or covered with a durable plastic mesh to provide a surface for bats to cling to.
- The house should be constructed from non-pressure-treated wood, such as cedar or exterior-grade plywood.
- A landing area extending three to six inches below the entrance must be included.
- To maximize heat absorption, the exterior should be painted with a dark, water-based, exterior-grade paint, such as dark brown or black.
Optimal placement is paramount for attracting bats, as they rarely use houses mounted on trees due to predator access and shade. The house should be mounted on a pole or the side of a building at a minimum height of 12 feet, with 15 to 20 feet being preferable. To ensure the required high internal temperatures, the bat house must face south or southeast to receive at least six to eight hours of direct sun daily.
The area around the house needs a clearance of 20 to 30 feet to allow bats an unobstructed flight path when leaving and returning. A house is most likely to be occupied if it is located within a quarter mile of a water source. People should avoid handling any bats they may encounter and instead observe them from a distance.