Just as the rigors of winter begin to fade, when days grow longer and weather becomes more clement, there comes the downside of spring: mosquitoes. It’s not as if they aren’t anticipated – they appear year after year, after all – but there’s always the hope that, somehow, this year there won’t be as many as before. But there always are. They swarm, they bite, they make that high-pitched annoying whine that makes a person hit himself in the ear, hard. This goes on for weeks, even months until everyone begins to wonder if winter had really been all that bad, snowdrifts and all, but at least mosquito-free.

Is there a way to make mosquito season more bearable? To at least reduce the sheer, overwhelming number of these insects? The answer is complicated. When trying to manage mosquito populations, the methods depend on a wide range of variables. It is possible to have an impact, but it takes planning, effort, and some costs.

Bats and Purple Martins

There has long been a commonly held belief that bats, purple martins and other flying insectivores, such as species of swifts, are voracious mosquito predators. Many people encourage the populations of these animals by providing martin houses and bat boxes so that they will establish themselves nearby and keep the mosquito populations down. From a common-sense point of view, this is reasonable: Bats and birds can be seen flying through clouds of mosquitoes, which should make these insects easy prey. Careful research has shown, however, that these animals simply do not eat an appreciable number of mosquitoes. Examination of stomach contents shows that not only the individual numbers of mosquitoes eaten is low, but that as a percentage of all food sources mosquitoes represent a minority of their prey. Larger prey (moths, flies, bees, beetles, and so on) provide more calories for the predator for the same effort; the energy budget balancing the effort of flying and the intake of calories from larger bugs makes hunting mosquitoes a losing proposition. Also, the overwhelming number of adult mosquitoes present makes this source of control inefficient. Even in areas where colonies of tens of thousands of bats are feeding regularly, they cannot make more than a small dent in a population of mosquitoes numbering in the tens and even hundreds of millions.

Dragonflies and Other Aquatic Predators

Some landowners who have mosquito problems try to introduce dragonflies or increase existing populations. Adult dragonflies do eat adult mosquitoes but, as with bats and other flying predators, they cannot even begin to make a difference in the overall population of adult mosquitoes. In the larval stage, dragonfly naiads prey upon mosquito eggs and larvae. Once more, the ratio of dragonfly naiads to mosquitoes does not allow for the population of the latter to be reduced by very much. Since dragonflies require similar conditions for breeding as mosquitoes, this balance in populations can really never be changed. There are other animals that prey on mosquito eggs and larvae, such as tadpoles and fish. In particular, the species known as the mosquitofish (Gambusia affinis) is known to eat large quantities of mosquito eggs and larvae. Native to the southeastern United States, this fish began to be transplanted to other states with mosquito problems, such as New Jersey, about 1905 and shipped later in the century to at least 50 other countries, particularly those with large populations of the malaria-carrying Anopheles species of mosquitoes. Not only does the mosquito fish reproduce well, it has a relatively high tolerance to variations in temperature, salinity and the presence of organic waste in the water in which it lives. Unfortunately, G. affinis does not prey on mosquitoes alone; they consume any insects, including dragonfly naiads, and have been responsible for the reduction of the populations of native fish (by eating their eggs) where they have been introduced. In the mid-1990s, the World Health Organization recommended that G. affinis no longer be deliberately introduced to any further areas. In the United States, the introduction of the mosquitofish is closely regulated by the states, and the use of the species for mosquito control is usually restricted to ponds or other artificial bodies of water that do not have any connection with other waters. Other species of fish have been considered and even field-tested for similar use, such as the common guppy (Poecilia reticulate), tropical cichlids (Tilapia zillii, Oreochromis mossambica and Oreochromis hornorum) and the so-called “annual” Cyprinodontidae species with drought-resistant eggs that can survive in temporary water sources. All of these species present similar problems as G. affinis, since they are also indiscriminate about which species they feed upon.

Traps and Electronic Bug Zappers

Although attractive means of mosquito control in theory, traps and electronic bug killers have not been shown to be ideal in use. Many consumers find them to be unpleasant, because of the necessity of disposing of the trapped insects or the sound of bugs being killed. These methods have also proved to be environmentally questionable since studies have shown that they kill far more beneficial insects than mosquitoes. In either case, as with live predators, their impact on populations of adult mosquitoes is minimal.

Controlling Breeding Areas

This can be divided into three courses of action: denying breeding conditions, spraying and biological control. Since mosquitoes lay eggs in areas with stagnant water, where larvae hatch and live until adulthood, reducing the number of areas with the right conditions for breeding works very well. Historically, swamps and marshes have been drained and filled to deny mosquitoes their breeding grounds, but it is difficult for private landowners in the United States to get permission, even on their own private property, to follow this method. Still, it is possible to take action that is both legal and effective: Getting rid of structures where stagnant water can gather (old tires, for example), using electric pumps to convert still water to moving (small ornamental water features, livestock water troughs and the like) and cleaning logs, fallen branches and other obstructions from creeks and streams which can allow still water areas to form can all reduce the amount of area where mosquitoes can successfully breed.

Although DDT is, unfortunately, banned in the United States (despite the fact that it has been proven that the historical root of that ban, Rachel Carlson’s book Silent Spring, had no scientific basis), there are a number of other sprays on the market that can help control mosquito larvae on water. The drawback, however, is that some can be indiscriminate in their actions, killing beneficial or neutral species. They also require specialized spraying equipment or contracting with commercial firms, repeated application is needed and, of course, the cost.

By far the most successful method of control for mosquitoes is a bacterium that can be applied to stagnant or slow-moving water. Named Bacillus thuringiensis var. israelensis (BTI), it produces a toxin as it grows. This toxin only affects mosquitoes and blackflies; it is harmless to everything else. Water treated with BTI not only safe for fish, frogs, turtles and other insects, it can be safely drunk by mammals, including wildlife, livestock, pets and humans. Widely available commercially in either pellet or tablet form, it can be easily applied to ponds, drainage ditches, livestock troughs or anywhere else where mosquitoes can breed. The bacteria are not persistent, so BTI has to be reapplied during the mosquito season. While not overly expensive (particularly compared to being swarmed by mosquitoes all summer), it is probably not economically feasible to use BTI over large areas, such as the entire state of South Carolina.


Mosquitos, even the non-malarial species, have been troubling humans for thousands of years. Their presence has restricted where men have lived and traveled, have influenced changes in the land – vast swamps and marshes have been drained to defeat them – and the reason for the existence of such a creature as the mosquito has been the center of serious theological debate. For a modern homeowner, the battle continues. The use of personal protection – sprays and other repellents, head nets, even screened-in porches, and patios – only represent an uneasy truce. Reducing shady areas and tall grass, where adult mosquitoes linger during the day, can expand where humans can comfortably travel, but it does not address the root problem. It takes an attack on mosquitoes’ breeding grounds, by eliminating stagnant water and using spray or BTI to kill larvae, to actually reduce their numbers. Mosquitos may be held in check, but it may never be checkmate until you call Bob Jenkins Pest & Lawn Services.