Summary of the Arrowwood Environmental report on bats

The Vermont Endangered Species Committee is currently evaluating a report about the potential harm to bats from the roadside spraying done in the BLSG Insect Control District. The report from Arrowwood Environmental is 19 pages long and details the science that suggests BLSG’s pesticides could harm or kill several species of bats on Vermont’s endangered species list. The report lists 70 scientific and agency references supporting its arguments and conclusions. Below is a summary of some of the main arguments in the report.

Five rare bat species live in the BLSG District

Vermont has nine species of bat, and five of them are on Vermont’s list of threatened and endangered species. All five of these rarer bat species have been found recently in the towns of the BLSG District. Two of the species are also on the federal endangered species list.

  1. Indiana bat (federally endangered and Vermont state endangered)
  2. Northern long-eared bat (federally threatened and Vermont state endangered)
  3. Little brown bat (Vermont state endangered)
  4. Tri-colored bat (Vermont state endangered)
  5. Eastern small-footed bat (Vermont state threatened)

In summer, all of these bats fly within the BLSG District foraging for insects and raise their young at roosting sites on trees, rock crevices, or structures in the District. Nationally significant maternal roosting colonies of the federally endangered Indiana bat are present in the BLSG District.  In winter, all of these bats hibernate in caves or mines where they can be exposed to white nose syndrome. This disease has caused serious reductions in population numbers of at least four of the listed bat species and is responsible for some of the species being listed as threatened or endangered. One of the hibernation sites is within the BLSG District.

Bats forage for insects at the same time BLSG sprays pesticides into the air

During the summer months when BLSG sprays pesticides along roads to kill mosquitoes, bats forage for insects in all five towns of the BLSG District. The pesticide spraying always happens after dark at the same time bats are flying in search of insects. The pesticide mist spreads 100 to 200 feet on either side of the road and a similar distance vertically. Every time BLSG sprays a road there is a good chance that bats will fly through the pesticide mist or eat insects contaminated with pesticide.

Bats are vulnerable to several routes of exposure to BLSG’s pesticides

Unlike most agricultural pesticide applications, BLSG’s pesticide mist is designed to stay suspended in the air for an hour or two. When bats fly through the mist the pesticide can be inhaled and also absorbed through the thin, exposed wing membrane. Pesticide can stick to bats’ fur and later be ingested when bats groom themselves or each other (by licking). Bats can also ingest pesticide when they eat insects that survive the mist but have become contaminated while flying through it (many medium or large insects may not succumb immediately to the pesticide mist). Female bats exposed to pesticides can pass the chemicals to their young through mother’s milk.  

A 2019 study by researchers in Europe confirmed that the potential harm to bats from pesticides has been seriously underestimated and should be reevaluated in light of bats’ unique vulnerabilities. The authors concluded that important risks that have not been sufficiently evaluated include 1) ingestion via contaminated insects and grooming, 2) absorption through the wing membrane, and 3) exposure of pups via milk.

Small amounts of pesticide can harm bats

Laboratory studies have determined that small doses of pesticides similar to those used by BLSG generally do not kill most test animals (typically birds, mice, or rabbits). But these results are not always applicable to bats. In a few tests with bats, small doses disrupted muscle control. Most bats recover from this toxic effect after a day and therefore those doses are not considered lethal. But in nature the effect would probably be fatal. Pesticides can also interfere with bats’ immune systems making them more susceptible to disease, including white nose syndrome.

The most common pesticide used by BLSG, permethrin, accumulates in fatty tissues in mammals. So tiny doses repeated throughout the summer can result in high body loads of pesticides. During migration or hibernation when fat reserves are burned, pesticides can be released quickly with toxic results. If this happens during migration flights, effects on muscle control could jeopardize bats. If a toxic effect compromises immune function during hibernation in communal caves or mines, bats may be less capable of surviving white nose syndrome.

Vermont’s endangered species law is strict

The Vermont endangered species law was written to provide strong protection for listed species. It is one of the strongest state endangered species laws in the country. The law prohibits activities which could result in a “take” which is defined as “an act that creates a risk of injury to wildlife, whether or not the injury occurs.” Although there has been no documentation of bats being harmed or killed by BLSG’s pesticide spraying, there is an obvious risk that these activities will cause injury or death to listed bats.

If Vermont’s Department of Fish & Wildlife is aware that a worthwhile activity might cause harm to endangered or threatened species, it requires the responsible group to have an incidental take permit. This permit specifies how a take might occur and how the group can carry out its mission while reducing the risk of a take occurring. BLSG does not have an incidental take permit for any threatened or endangered species.

The Vermont Endangered Species Committee’s Mammal Scientific Advisory Group is currently reviewing the Arrowwood report and will advise the Committee in the next month or two. The Committee can then advise the Secretary of the Agency of Natural Resources about the potential need for an incidental take permit.

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