Each of the six species of bats that are affected by WNS are obligate insectivores--many of which feed on insect pests of agriculture and garden crops, and at times these may include insect species that pose risks to human health. The enormous number and biomass of insects that would have been eaten annually by the estimated 1 million bats that have since died in the northeastern U.S. emphasizes the extraordinary value of insectivorous bats to the normal function and health of both the terrestrial and aquatic ecosystems in which they feed.
During the warm months of the year, one little brown bat (Myotis lucifugus), a species that has been most affected by WNS, is known to consume insects ranging from one-half to its entire body weight in a single night. Extraplolated to entire colonies and populations, this level of insect consumption provides an important ecosystem service to human kind, which in turn can reduce the use of pesticides often used to kill insects.
For example, assuming that, on average, one little brown bat that weighs 7 grams eats only half its body weight each night (3.5 grams) from April 15 through October 15 (~180 nights), this would amount to the consumption of 3.5 grams x 180 nights, or 630 grams of insects annually during these warm months. If we multiply 630 grams of insects that can be consumed by one little brown bat times 1 million bats that have already died from WNS, this would amount to 630,000,000 grams of insects that would not have been eaten by bats. When the latter value is converted from metric to English units, this amounts to about 1,388,912 pounds or 694 tons of insects. This biomass is equivalent to the weight of approximately fifty-six M113 fully-equipped armored personnel carriers, twenty-three M3A3 Bradley fighting vehicles, seventeen fully-loaded 18-wheelers, 6 female blue whales, or 5,555,648 quarter pounders--take your pick for comparison.
The level of nightly consumption by one little brown bat would be equivalent to a 150-pound teenage boy eating approximately 300 quarter-pounders. Translated to the number of insects that would not be eaten by one little brown bat in your backyard on a given night, it amounts to the equivalent of 60 medium-sized moths or over 1,000 mosquito-sized insects. On average, this means that approximately 10,800 medium-sized moths or approximately 180,000 mosquito-sized insects each year would not be eaten by just one bat.
Although no studies have been conducted to assess the ecological or economic impact of insectivorous bats on ecosystem in the northeastern U.S., Cleveland et al. (2006) conducted a study in south-central Texas, and have shown that within an 8 county region, the quantity of insects eaten on an annual basis by an estimated 1.5 million Brazilian free-tailed bats saves farmers an average of $741,000 per year in reduced applications of pesticides needed to control cotton bollworm on cotton crops.
Wisconsin DNR Informational Meeting:
White-Nose Syndrome and the Federal Advisory on Bat Cave Closures
January 6, 2010