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Bug-eating bats help control garden pests

  • Nanette Londeree
  • Being bugged by pesky mosquitos or moths? Want some help reducing their numbers? Encourage bats to hang around.

    Often having the undeserved reputation of nighttime villain, these furry, winged mammals are beneficial to the environment — consuming huge numbers of night-flying insects, pollinating plants and dispersing seeds. As long as they’re not roosting under your roof, it’s a good thing to have them flitting about your garden while you sleep.

    While not likely to win awards for cuteness, these shy, gentle and intelligent little creatures belong to the family Chiroptera, meaning “hand-wing.” The flexible wing structure is much like a human arm and hand, except it has a thin membrane of skin extending between the “hand” and the body, and between each finger bone. The “thumb” extends out of the wing as a small claw, which bats use to climb up trees and other structures. They can see just fine, though their dominant navigational method, like dolphins, is echolocation, sending out beeps and analyzing the echoes that come bouncing back. With this finely honed ability, they can detect obstacles as fine as a human hair in total darkness.


    This diverse group of mammals has more than 1,200 species with the pallid bat, the big brown bat, the Mexican free-tailed bat and other Myotis species being the most common in our area. More than two-thirds of bat species consume, with extraordinary appetites, nocturnal insects like moths, gnats, beetles and crickets. A single little brown bat can eat up to a thousand mosquito-sized insects in a single hour while a nursing mother will devour the equivalent of her body weight each night. Bats will fly from half a mile to sixmiles from their roost to a feeding site, using temporary roost sites there until returning to their main roost.

    Most of the remaining species feed on the fruit or nectar of plants, playing vital roles as plant pollinators and seed dispersers. And vampire bats? There are three species, all living in Latin America that feed on the blood of cattle, horses and wild mammals. They don’t suck blood Dracula-style; after finding a thin-skinned spot on the animal, they make a small incision and lap it up like kittens do milk.


    Bats have a relatively long life, five to 30 years depending on the species; they’re about the slowest mammals to reproduce for their size, and usually produce only a single pup. At birth, the baby bat will weigh in at about a quarter of the mother’s weight, and will be cared for in maternity colonies where females congregate to bear and raise their young.

    Insect-eating bats roost in tree foliage and cavities, under loose bark and in caves and crevices. As their natural habitats continue to disappear, more species are taking up residence in buildings and homes. Mounting a bat house on your property is one way to provide a safe place for them to live while protecting your garden from night-flying insects.


    Bats living under your roof can cause problems with accumulation of fecal droppings (guano) and urine that accumulates and stains ceilings and walls. Not only are these waste products undesirable, they can attract other insects and have a strong, unpleasant odor. They have the potential for transmitting disease, particularly rabies, so be sure to vaccinate your dogs and cats against rabies.

    Generally, sick bats will be on the ground, so don’t pick one up or handle it. For assistance, you can contact WildCare in San Rafael; its Wildlife Hotline, 415-456-SAVE (7283), offers guidance on what to do if you find injured or orphaned wild animals in your home or garden.

    Some summer evening, find a spot in the garden right after sunset, and for the next hour, watch for these shy little critters swooping about in search of a meal. With a little information and understanding, you can protect a piece of their habitat right in your own back yard, and reap the benefits.