What are Mosquitoes’ Natural Predators?
Gambusia fish swimming among mosquito larvae.
Mosquitoes have a variety of natural predators, from bats to fish to dragonflies. Scientists have studied what eats them in the wild, in hopes of finding enemies that can be introduced to get rid of mosquito problems near where people live. Some predators eat enough to noticeably reduce the population, while others get rid of so few that one can barely tell any difference.
A lot of the predators that you actually see out catching bugs are the least useful, specifically, when it comes to mosquitoes. Maybe purple martins and bats won’t eat anything, but their choice of bugs is large enough that mosquitoes make up only a small part of their diet.
Bats, birds and dragonflies which kill adult mosquitoes are some of the most obvious predators, but the least effective, according to the book Medical and Veterinary Entomology.  Mosquitoes make up only a small part of their diet. Fish, insects and other creatures that feed on larvae are another possible form of control, though still only effective in certain circumstances. One of the most effective natural enemies is Bacillus thuringiensis israelensis or Bti, a bacterium that only targets mosquito larvae plus a few very closely related species, without affecting fish, frogs or other desirable species, including people.
Two natural predators which attack mosquito larvae in the water are mosquitofish and dragonflies:
The gambusia fish (Gambusia affinis), also called the western mosquitofish, eats mosquito larvae. These little fish are controversial because they’re aggressive, also eating the eggs, larvae and young of native fish and amphibians and competing with them for other food. They’re not always successful at controlling mosquitoes, with unpredictable results. There is also a related species, Gambusia holbrooki, the eastern mosquitofish, which is sometimes used for mosquito control too.  They’re tiny, grayish fish.
People have tried stocking gambusia to control mosquitoes in various areas of the United States since the early 1900s, with varying success. Due to the harm to native wildlife, mosquitofish are regulated in many states, where they may only be stocked in enclosed ponds or pools that have no outlet to streams or rivers, so the fish can’t escape into the wild. A permit may be required.
The Rutgers Center for Vector Biology reported on several tests of mosquitofish in various situations. In an unused swimming pool, they stocked 35 fish each spring, since freezing of the water’s surface caused them to die off in the winter. The fish ate all the larvae of Culex and Aedes mosquitoes, and also ate Anopheles mosquito larvae if there was no floating vegetation. If there was vegetation on the surface, such as might be found in an ornamental lily pond, the Anopheles larvae used it to hide and the gambusia fish couldn’t control them.
A mosquitofish snacks on a mosquito larva.
The Virginia Department of Game and Inland Fisheries suggests the fish are “somewhat effective” in ponds, drainage ditches or containers, but also cautions they must not be able to escape through an outlet into other water. Gambusia may also overwhelm local native species, including dragonflies, killifishes or topminnows, which also control mosquitoes, so there may be no actual improvement in the problem, just a change from one kind of fish to another.
Gambusia are best used in isolated, artificial bodies of water with little to no surface vegetation. If you’re interested in the possibility of using them for mosquito control in your area, contact your state’s fish and game or wildlife department to find out restrictions and recommendations. In certain limited circumstances, they may work, but in others they may not work, or do more harm than good.
Other fish also eat mosquito larvae, so gambusia aren’t the only choice. The popular and ornamental Koi fish are too large to feed on tiny mosquito larvae, but smaller guppies, killifish or common goldfish will live alongside Koi and eat them. This article discusses other fish which also eat mosquitoes.
The larvae can live in water too shallow for even small fish to reach them, so if you want to use fish to control them, make the sides of the pond steep, so there’s little shallow water at the edges.
Dragonflies are natural enemies of mosquitoes in all their stages of growth. Dragonfly larvae live in the water like mosquito larvae and feed on them, while adult dragonflies eat adult mosquitoes.
The problem is that dragonflies also eat other things. When the mosquito population starts to get low, the dragonflies will choose other prey instead, leaving fewer mosquitoes than before, but not eliminating the problem.
A dragonfly waits for prey.
Dragonflies also require a habitat similar to mosquitoes, so adding standing water to attract dragonflies will attract mosquitoes as well. If an area is already free of pools and puddles, better to leave it that way and try to deal with the mosquitoes that fly in from elsewhere in some other way. Fish which eat mosquito larvae will also eat dragonfly larvae, so both fish and dragonflies may live in balance in nature, but they’ll compete with each other if you’re trying to get them both to multiply so they can overwhelm the mosquitoes.
An experiment in Yangon, Myanmar, in Asia, showed that dragonfly larvae could be introduced to successfully control mosquitoes that were breeding in large containers of drinking water.  But like gambusia, dragonfly larvae work best under specific conditions, such as small artificial ponds or other containers of water where there are few other insects to eat besides mosquito larvae, and no vegetation for the mosquitoes to hide in, and no competing fish or other wildlife.
In the United States, pest control experts discourage purchasing dragonflies for mosquito control, since other alternatives are more effective in most circumstances. Purchased dragonflies will probably not be local species, and introducing non-native species may cause more problems to the local ecosystem.
Purple martins eat more insects than just mosquitoes.
Purple martins have gained a reputation as natural mosquito predators, and they do eat adult mosquitoes, but they eat most other kinds of flying bugs, too. No research has shown that mosquitoes are more than 3 percent of their diet, according to an article in Missouri Conservationist magazine.  The results seem logical, since martins catch insects during the day while flying high in the sky, but mosquitoes usually fly close to the ground looking for prey to bite, and are most active after dark. Claims that these birds can eat 2000 mosquitoes a day are based on a hypothetical diet eating nothing but mosquitoes–something that no purple martin actually does. 
Purple martins are still good to have living nearby, since they eat lots of other insects that humans don’t want around, including garden pests like cucumber beetles and Japanese beetles. Unfortunately, they also eat some other mosquito predators like dragonflies.
You can encourage these graceful, beautiful and useful birds to live in your yard by erecting purple martin houses, and they’ll work to control insects in general, but don’t count on them solving your mosquito problem. Houses need mounted high on a pole, and can range from simple gourds to ultimate deluxe accomodations like this, but if you’re planning to try to attract these birds, ask an extension agent or read up on specifically to see what they need in your area.
Bats are sometimes also promoted as mosquito predators. They do eat mosquitoes, and since they fly at night, they’re out at the right time to catch them. The problem is that they also like a variety of food, and will eat many kinds of insects, so mosquitoes make up only a small part of their diet. Little brown bats showed only 1.8 percent mosquitoes in their fecal pellets, compared to 71 percent moths and 16.8 percent spiders, according to one study. The diet of big brown bats was mostly beetles and caddisflies. 
Bats may have received an exaggerated reputation as mosquito predators, based on a 1958 study on their ability to find insects by echolocation.  Enclosed in a room with mosquitoes, bats could catch on average between 1 and 9.5 per minute, which other people have extrapolated into what they could catch in an hour. But a bat that could catch almost 10 mosquitoes a minute for fifteen minutes in an enclosed room would catch much less than that, out in the wild, with a variety of insects flying in the open air.
Like purple martins, though, bats do eat many insects that are annoying or harmful to humans and their gardens, so encouraging them in the neighborhood has benefits, even if it won’t significantly reduce the population of mosquitoes.
Bats prefer beetles or moths to mosquitoes.
Bat houses are best placed in isolated locations, at least 12 feet above the ground, with at least 20 feet of clear space for a flight path into the house. They like to live within a quarter mile of water, so they can drink and also so there will be plenty of insects–but lack of food isn’t a problem if you want to attract them to get rid of insects!
Though you might think they prefer homes in cool dark places like caves, they actually like warm, sunny locations, so a southern exposure is best. Mounting a house on the exposed side of a barn is better than in a tree, which is shaded and makes the house accessible to raccoons and cats.
The best time of year to install a bat house is in winter or early spring before they have returned from their winter migration. When they come back north in the spring, they’ll begin looking for places to occupy. One study of 28 houses showed that bats found them mounted on buildings or poles in an average of 71 to 73 days, but it took them an average of 255 days to find them mounted in trees. 
The University of Nebraska Extension Service recommends placing the house over ornamental plantings so pets and children are less likely to find and pick up any baby bats that fall out of the house. For more information on bat houses, see their website on Bat House Construction and Installation.
 “Purple Martin Mania” by John Miller, Missouri Conservationist, March 2006
Purple Martin photo by Rick Kimpel, Wikimedia Commons. Bat photo courtesy of the CDC.
Other Educational Resources
Learn more about mosquitoes with the following resources: