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Bats in the Garden

Though frequently maligned and feared, the bats of Pennsylvania manage insect pests of our crops, making them true friends of gardeners.

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Updated:

June 25, 2025

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Little brown bat. Photo: USDA Forest Service - Southern Research Station , USDA Forest Service, SRS, Bugwood.org_Licensed CC BY-NC

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I have fond memories of warm summer evenings sitting under the flowering crabapple tree in my family's backyard. We watched twenty or so bats come from the neighbor's two-story garage at dusk. The bats fluttered a bit, then headed directly to our pond for their nightly drinks. We'd watch the bats feeding over our garden and the surrounding fields until it became too dark for us to see them. In October, as the evening's darkness came earlier and the air cooled quickly, we spent less time under the crabapple. The bats' nightly forays also ended. We knew the bats had relocated to coal mines to spend the winter in a temperature-controlled habitat. We anticipated their return to George's garage in the spring before the crabapple blossomed.

I was always surprised by the misconceptions many folks held about bats. As the city folk came to escape the heat of nearby Wilkes-Barre, we'd offer them a lawn chair under the crabapple tree. As the bats emerged, my mother was warned to cover up her permed hair to avoid having a bat become entangled. We country folk lived dangerously, according to our guests. We could subtly encourage the city dwellers to go home if they overstayed their welcome. Mom suggested I turn on the light at the corner of Dad's honey house. Soon, insects would be swarming around the light. If that didn't send the guests to their car, we waited patiently. There was never a need to say anything. The bats would begin swooping through our yard, feeding on the teeming insects. That's when folks decided to call it a night. We had yellow bulbs in all the other outside lights, but not that one. I still chuckle about that strategy.

Worldwide, there are over 1,300 species of bats. All bats are mammals of the group called Chiroptera, which means hand-wing. The Chiropterans are the only mammals capable of true, powered flight. Pennsylvania has nine species of bats with wingspreads from 8 to 16 inches. Three species migrate to warmer areas of the United States for the winter. The remaining six species move into the constant temperature of a cave to hibernate. Within the order, Chiroptera is Pennsylvania's insect-eating bats of the family Vespertilionidae. While some bats in North America do feed on fruit or pollinate flowers while gathering nectar, none are in the northeast. An insectivorous bat takes insects on the wing, often catching the insect on the skin between its legs, then transferring the insect to its mouth. Bats' sharp teeth break their food into tiny bits for easy digestion. A bat consumes at least 25% of its weight in a single feeding.

Bats have tiny, beady eyes but see very well. Bats' ears are large and exceptionally well-developed. Their ability to echolocate enables them to be successful predators of insects and navigators of small spaces. As a bat flies, it utters high-pitched squeaks, which echo off nearby objects. Split-second reflexes help bats change flight direction to capture prey or avoid obstacles.

Most female bats mate in late summer and store the sperm until spring, when fertilization occurs. The young, born in the summer, are blind, naked, and helpless. Like all mammals, the babies are nursed by their mothers. Maturing quickly, most young bats are self-sufficient and nearly full-sized by six weeks old. Many bat species give birth to only one young annually.

All of Pennsylvania's bats prefer to make their feeding flights in the late afternoon, evening, and early morning. None are daytime flyers unless their roost has been disturbed. During the day, depending upon the species, they roost singly, in pairs, or groups. They hang upside down by their feet. Bats seek secluded, dark places to roost. Hollow trees, caves, rock crevices, and even loose tree bark will shelter them during the day. Vacant buildings, barns, church steeples, and attics are favorite human-made structures for sheltering bats.

Our non-migratory bats are true hibernators in caves and mines. They eat nothing during the winter, surviving on stored fat in their tiny bodies. Their body temperature drops close to the above-freezing air temperature. Several different species may hibernate together. A frequently fatal disease, white-nose syndrome caused by the fungus, Pseudogymnoascus destructans, may cause 90 to 100% of hibernating bats to die. Researchers discovered this disease near Albany, New York, in 2007. It has spread throughout thirty-three states and seven Canadian provinces in the northeast. Please pause and reflect: Many bat species give birth to only one young annually. White-nose syndrome may cause 90 to 100% of hibernating bats to die.

What can we do to help bats, and why should we assist these often-maligned creatures? First, do not disturb bats when they roost! Never enter a cave or mine where bats hibernate. You can be an unwitting vector for white-nose syndrome to other locations. Second, a bat uses its limited energy stores when it is disturbed during hibernation. Disturbing bats during the summer can cause death to the few young produced each year. Bats active during daylight hours are subject to predation by daytime hunters.

Remember that all of our Pennsylvania bats are insectivores. As my family sat under the crabapple tree, mosquitoes rarely pestered us. A single bat can easily consume one thousand mosquitoes in an hour! Do you realize that many of our most serious garden and agricultural pests are active at night? Cucumber beetles (Acalymma spp. and Diabrotica spp.) are most active from dusk to dawn. The beetles feed on cucurbits (cucumbers, melons, pumpkins, gourds, and squashes), legumes (beans and peas), and nightshades (tomatoes, eggplants, peppers, and potatoes). Over 280 species of plants are affected by cucumber beetles. Striped cucumber beetles serve as vectors of bacterial wilt (Erwinia tracheiphila). Even the larvae of cucumber beetles are agricultural pests called corn rootworms. As we think of corn, consider those caterpillars that surprise us as we shuck a fresh ear of corn. Those fat corn earworms come from eggs laid by a moth that flies at night. Bats reduce the need for pesticides used to manage destructive insects.

After spending all day in a hot environment, bats need to rehydrate each evening. Unlike birds that enjoy a drink while perched on a small bird bath, bats drink water while flying low over the surface of a pond. Most bats prefer an open water surface at least 10 feet long and 2.5 feet wide to quench their thirst.

Perhaps providing a watering space for bats isn't possible for you. Can you provide flowers that open or remain open at night? Fragrant flowers are especially attractive to our night-flying moths. Don't worry. The bats won't harm the flowers as they feed on the insects. Consider installing a moonlight garden of white or pastel flowers where you can relax each evening.

Our newer homes have few nooks, crannies, or attic spaces to support bats. Consider installing a bat house in your yard. Be warned that bats are much fussier than birds when accepting summer housing! Bat houses must be of the correct dimensions, properly oriented to the sun, and installed at the correct height. Most ready-made bat houses are too small to maintain an even, warm temperature. They become shelters for wasps. The Pennsylvania Game Commission and Bat Conservation International provide plans for bat houses with the correct design, construction, and siting information.

Often, residents are upset to discover that bats share their homes. It may be a two-season process to eliminate the bats. During the first season, determine where the bats are entering the house. Do not try to exclude them immediately! You will likely trap bats, especially infant bats, within their roosting space. Instead, wait patiently until the bats depart in October to migrate or hibernate in a cave. Then, close up their entry point before they return in the spring. While you are waiting for the bats to vacate naturally, why not install a bat house so it will be ready to welcome them back to the neighborhood?

Should you be concerned about bats and diseases? Be prudent! Never, ever contact a bat. Like all mammals, bats can carry rabies, but not more frequently than any other mammal. Bat manure, called guano, is an excellent soil amendment, but again be prudent. The fungus Histoplasma may be in bird and bat manures. Take care when handling and using all manures. What about SARS-CoV-2, the virus that causes COVID-19? Bats are natural hosts to coronaviruses, as is other wildlife. Bats with coronaviruses in the wild are not a threat to human health if left undisturbed. Our small insectivorous bats in Pennsylvania are not closely related to the large bats used as food in Asia.

Let's celebrate bats all year 'round, not only during Bat Appreciation Month in October. These unique animals are a gardener's friend!