Bats for Mosquito Control

Bats are, famously, one of the mosquito's natural predators. According to some experts, a single brown bat can gobble up to 1,000 mosquitoes in a single hour. 

So says a recent article in the Miami New Times. Or maybe it's more according to Mother Earth News:

Many bats, and almost all in the United States, thrive on an insect diet. A single bat can eat up to 1,200 mosquito-sized insects every hour, and each bat usually eats 6,000 to 8,000 insects each night.

Really? That's a lot of mosquitos. Just where did this number come from? The Miami New Times article quotes a town supervisor in New York. The Mother Earth News article doesn't provide a reference.

Variations of that quote are everywhere on the internet. The Tampa Bay Times uses it all the way back in 2001. It seems that most articles that use that figure don't really point to where it comes from.

Not on a mosquito diet

So, is it true that bats can eat 1,000 mosquitoes per hour and are bats a good way to control mosquitoes? Questions that are taken as a given in many articles should be questioned.

The only reference to bats eating a large number of mosquitoes that I find comes from an article from 1926 in the Journal of Mammalogy. It quotes a 1920 study where bats were released into a room full of mosquitos and in the first few minutes ate on average 10 per minute. That comes to 600 per hour and was later rounded up to 1,000 (or even 1,200).

So, are bats good at catching mosquitoes? Probably not as good as people hope. To understand that you have to look at the size difference between a bat and a mosquito. The most common bat in Florida is the Brazilian Free-tailed bat with an average weight is about 12.5 grams. The average weight of a mosquito is 2.5 mg or about .02% of the bat's weight.

Mammal and bird predators rarely hunt things that are only .02% of their weight. For example, we wouldn't expect a tiger that weighs 88 kg to hunt wood roach (palmetto bug) with a weight of 2 grams, but it's about the same ratio as a bat hunting mosquitoes. There are a few mammal hunters that specialize in prey that small but they have to get it in large quantities. Baleen whales eat huge mouthfuls krill at once and anteaters tear into ant or termite hills to get many quickly.

I don't eat roaches

Texas Tech says that the Florida's most common bat, the Brazilian Free-tailed Bat's menu consists of:

moths (34%), flying ants (26.2%), June beetles and leaf beetles (16.8%), leafhoppers (15%), and true bugs (6.4%).

Bats are very opportunistic feeders. I'm sure that in other areas and other times of the year the diet would be different. But the size of the prey wouldn't change that much. These insects range in weight from .5 grams - 2 grams, much larger than the .0025 grams of a mosquito. Or to put it another way, a bat can spend his time and energy catching 1,000 mosquitoes or 1 good size moth.

Maybe there are references that lend credence to the quote. If anybody knows of any I'd love to see them.

Escaped the bat again

I write this blog mostly as a way to learn about a subject and to organize my thoughts. In this case I had seen the "bats eat 1000 mosquitoes per hour" quote several times with little backup. When many people use a quote but nobody knows where it came from it's probably not nearly as true as people assume. My conclusion is that this one is probably not true at all.

Bats are an integral part of the ecosystem. They do control some larger insects like corn moths and flying beetles and do eat mosquitoes. But as to mosquito control they're probably not nearly as effective as predators closer to the mosquito's size such as skimmers and dragonflies. And fish eating the larvae are even more effective. Because they're not that effective in controlling mosquitoes shouldn't diminish their worth.