A Myth is Born – Do Bats Eat Mosquitoes

I am sure you have heard the stories; a small bat can eat 1,000 mosquitoes a night. This idea is so well known that many people have put up bat houses to attract this animal even though most people hate bats. I guess they hate mosquitoes even worse.

It all makes so much sense. Bats fly at night eating insects. Mosquitoes come out at night to hunt us. Why would bats not eat this plentiful food? And then there is the science; scientists studied bats and determined they could eat 1,000 mosquitoes a night.

In this post I will look at this myth and explain how the myth originated. It is quite rare for me to be able to know how a myth starts, but in this case it’s fairly clear.

Science, Bats and Mosquitoes

In 1960 a paper was published called, The Echolocation of Flying Insects by Bats. This study found that a bat could eat 10 mosquitoes per minute or 600 an hour, which eventually got reported as 1,000 per bat, every night.

This science seemed to prove that bats eat a lot of mosquitoes each night, but the conclusion was flawed.

First of all, the bats were released in a closed room, and given only mosquitoes to eat. Well, any half intelligent bat will eat whatever it’s given.

No part of this study looked at what bats do outside of the lab.

The individual bats were selected because they were proven hunters. Remember that the scientists were interest in figuring out how bats find their food. It had noting to do with their diet.

Only one bat captured 10 per minute. Others were as low as 2 per minute. This is a common mistake made by reporters of scientific news – the best case value was reported, not the most realistic value.

These mistakes led the general public to start reporting that bats eat a lot of mosquitoes, as many as 1,000 a night, and that they are good at controlling populations. Nothing in this statement is supported by the above mentioned study, nor did the study reach this conclusion. It was the writers reporting on the study that made these claims – not the scientists.

More Science

There has not been a great deal of research on this topic, but there have been some good studies.

One study looked at the “taxonomic richness of mosquitoes in the diets of little brown and big brown bats“, which are common in the US and Canada. They looked at the DNA of bat fecal material to determine which species of mosquito were eaten. Mosquitoes were detected in 72% of samples from little brown bats and 33% of samples from big brown bats. The number of mosquito species eaten by little brown bats was also higher than for big brown bats.

In summary, brown bats do eat mosquitoes, but not all colonies eat mosquitoes. Small bats are more likely to eat mosquitoes and tend to feast on a larger number of species.

An Australian study looked at fecal mater from five local bat species. A total of 40 insect species were detected and moths were the most prominent. Mosquitoes were only detected for two of the five species. They concluded that smaller bat species are more likely to eat mosquitoes, and that not all species of bats eat mosquitoes. “There is a species-specific relationship between bats and their preferred meal.”

Little brown bats observed in a barn in Alaska showed that bats do use echolocation to find mosquitoes and that the mosquitoes “did not show any defensive behavior in response to approaching bats.” That is why devices that mimic bat sounds don’t work for keeping mosquitoes out of the backyard.

Another study looking at little brown bats in Alaska found that only 2% of their diet was mosquitoes.

A study of the little brown bat in New Hampshire found that when mosquitoes were very plentiful, bats consumed significant numbers.

A study in Sweden looked at the northern bat and found that, “In summer, northern bats rely heavily on mosquitoes and other dipteran insects, particularly in the north where summer nights remain light, and most feeding takes place in forested areas. In the south, the same species of bat feeds over lakes and farmland, and their diet varies accordingly, including dung -beetles, moths, and caddis flies as well.”

Do Bats Eat Mosquitoes?

There are 1,000 species of bats in the world and very few have been tested to see what they eat. Some don’t eat insects at all, but even the ones that do, have species-related diets. You can’t reach any conclusion about all bats. The right answer is, some do and some don’t, and this changes based on the environment.

Smaller bats are more likely to eat mosquitoes than larger ones.

Bats are opportunistic. When they are hungry, they eat what is available. Mosquitoes don’t take evasive action like other insects, so mosquitoes are easy to catch. Unfortunately, they are very small and so a bat might chase a larger more difficult prey in order to get a decent meal.

When mosquitoes are plentiful, as is the case in Northern Sweden, bats eat more mosquitoes. When mosquitoes are less plentiful they eat fewer and rely mostly on beetles, wasps, and moths.

We can say some bats eat mosquitoes and in some cases mosquitoes make up a good part of their diet. The often quoted “bats eat 1,000 mosquitoes a night”, is not based on real world science and is a myth – in most cases.

Do Bats Control Mosquito Populations

Gardeners don’t really care if bats eat mosquitoes. What they want to know is, can bats control the mosquito population? Are bat houses a good way to keep them out of the garden?

The American Mosquito Control Association reports the following story, “During the 1920’s several bat towers were constructed near San Antonio, Texas, in order to help control malarial mosquitoes. Mosquito populations were not affected and the project was discontinued.”

Shelly Redovan, head of the Florida Mosquito Control Association, says, “the state of Florida has tried using bats to control mosquitoes. They tried bat towers, bat houses, and they were a dismal failure.”

The bat tower pictured here was built in Florida to control the mosquito problem. However, when the bats were put in, they supposedly flew away, never to return.

Mr. Tuttle, an expert and proponent of bat conservation, admits that, “simple provision of additional roosts should not be promoted as more than one step in the right direction toward solving mosquito problems. In some cases bat houses may help and in others, they may not.” (reference link for this is no longer available) There is no scientific evidence that bat houses reduce the local mosquito population by any significant amount. Any mosquitoes that are eaten are likely replaced from neighboring gardens.

Before setting up a bat house to control mosquitoes you should confirm that you have some of the smaller bats in the area and that they eat mosquitoes. It is much more difficult to get bats to inhabit a purchased bat house than is suggested by manufacturers of these homes. Putting up a bat house is a good idea; bats need all the help they can get. Just don’t expect relief from the skeeters.