Natural Mosquito Control
Natural predators like bats, frogs even fish can play a part in mosquito control. Find out how and what you can do to encourage them.
Bats are primary predators of vast numbers of night flying insects. Some species, like the little brown bat have been reported as consuming large numbers of mosquitoes - up to 2000 a night. However most of this data has been collected from 'controlled environment' studies where the bats were only offered mosquitoes.
Bats are known to be opportunistic feeders and will eat whatever food source is available. While they will eat mosquitoes, they don't go out and specifically hunt them. According to the American Mosquito Control Association, there's no question that bats do eat mosquitoes, however there's no evidence that increasing the bat population in an area will reduce the number of mosquitoes enough to affect human biting rates.
As a method of mosquito control I'd give them a 3! However bats do us a great service by eating a huge amount of other flying insects and pests that would like to eat our crops.
The map below shows the economic benefits that we get from bats eating pests that would damage crops.
As far as natural born mosquito killers go, Gambusia Affinis aka the mosquitofish, is beloved by mosquito control districts across the country. Originally introduced into California in the 1920s, they have been one of the most effective non-insecticidal and non-chemical methods of controlling mosquitoes for over eighty years.
Voracious feeders that will eat almost anything, an adult mosquitofish is capable of consuming up to three times their body weight in mosquito larvae - that's up to 500 larvae per day! A dozen Gambusia are good for about 48 surface feet of water.
This live-bearing American fish is hardy, capable of surviving in stagnant water and will grow only to about two inches in length
So for chemical free mosquito control give them a go. Most local mosquito control programs use the fish and often provide them for free to homeowners with mosquito problems.
Frogs, Toads and Tadpoles
If you're not interested in having fish, consider tadpoles. Some species of tadpoles (Scaphiopus hammondi) not only eat mosquito larvae, but they grow up to become toads (spadefoot toad) which in turn will eat mosquitoes.
Although only a few types of tadpoles will eat mosquito larvae, they do compete with the larvae for food. In one study, the presence of tadpoles meant that mosquitoes had a harder time getting enough food to survive and turn into adults.
However while frogs, toads and their young (tadpoles) are often touted as excellent for mosquito control, in reality they won't consume enough to put a serious dent in any large mosquito population.
The purple martin is an excellent example of a natural mosquito predator who's mosquito controlling ability is much exaggerated. During daylight, purple martins often feed voraciously upon dragonflies, known predators of mosquitoes. However at night, when mosquitoes are most active, purple martins tend to feed at treetop level, well above most mosquito flight paths.
According to the American Mosquito Control Association, "The number of mosquitoes that martins eat is extremely insignificant, and they certainly don't control them. In-depth studies have shown that mosquitoes comprise no more than 0 to 3 percent of the diet of martins".
While purple martins don't eat a lot of mosquitoes, they are a beautiful bird to have in your backyard. Rather than erecting martin houses specifically to attract insect-eating birds for mosquito control, build them for their aesthetic and educational value and consider the amount of mosquitoes they eat as a small bonus.
Dragonflies or Mosquito Hawks
Dragonflies are often referred to as "mosquito hawks" for their supposed ability to kill thousands of mosquitoes. Though they do consume their fair share of mosquitoes, dragonflies like most natural predators of mosquitoes do not consume enough mosquitoes to cause a significant impact on mosquito populations in the wild.
Most aquatic turtles are general predators, with a diverse diet. Experiments using red-eared slider turtles (Trachemys scripta, Fig) in Honduras revealed their ability to consume mosquito larvae. The turtles were placed in water-storage tanks and observed over a 2 year period. During that time, no mosquito larvae were known to emerge from any tank that contained a turtle. However the supply of mosquito larvae and other natural food wasn't enough to sustain the turtles, and they required supplemental feeding to maintain good health. In fact families welcomed the turtles as pets and fed them kitchen scraps.
If you're thinking about keeping aquatic turtles, then depending where you live, some species may be more suited than others. Red-eared sliders for example are quite hardy and adaptable. Secure fencing and pond depth will also be a consideration. Some turtles can handle a deeper pond (red-eared sliders) while some turtles prefer to be in shallower water. So again you need to consider the natural habits of the turtle species when planning your pond.
Pesticide Resistant Mosquitoes
The CDC (Centers of Disease Control and Prevention) have an open stance on insecticides and pesticides and caution that spraying chemical pesticides intended to kill adult mosquitoes, is usually the least efficient mosquito control technique. Not only does spraying have a detrimental effect on the environment but over time mosquitoes can develop resistance to the pesticides used, rendering them ineffective.
In a recent paper Pests Resistant to Pesticides the authors reported that pests that were once major threats to human health and agriculture, but were brought under control by pesticides, are on the rebound. Mosquitoes that are capable of transmitting malaria are now resistant to virtually all pesticides used against them.
The Environmental Protection Agency (EPA) also encourages non-chemical mosquito control measures. So anything and everything that can be done to encourage natural predators as a way of reducing mosquito numbers can only be good. Natural aerial predators, like dragonflies, birds, and bats, do have a role to play, but because they don't confine themselves to eating adult mosquitoes only, will have limited impact on large mosquito populations.
Unfortunately mosquito control is a complex problem that won't be solved by a single approach, be it bat houses, fish ponds or pesticides.