Apr 22, 2006 4 min read

I’m waiting for the arrival of Die Fledermaus. Not the German opera, but bats. The end of April and into early May is the time of year that hibernating bats in our area will begin to emerge from caves, mines and other structures that have been sheltering them through the winter.

A common nickname for a bat is “flying mouse,” but bats are not mice. In fact, they are not even rodents. They are in a separate order of animals. And what curious animals they are!

Bats are the only flying mammal in the world. Their wings are made from two layers of very thin skin, with only blood vessels sandwiched in between. This wing membrane is connected along a bat’s fingers-which are very long and narrow. From the “little finger” the membrane attaches to the ankle, completing the wing.

A bat’s thumb is a tiny claw at the bend of its wing. Bats use these claws to climb and crawl.

A bat’s toes also are small claws that curl towards its belly. This is opposite the direction our toes curl, and those of most animals. Nonetheless, bats use their claw toes to hang from rocks, wood and other surfaces when they roost or hibernate.

Even though bats have good eyesight, they use echolocation to navigate when they fly at night. You may have heard of sonar. It is the same process.

Here’s how it works: A bat emits a high-frequency sound and waits for the sound to bounce back off of objects in its path.

Guided by the bounced-back sound waves bats can fly quickly and surely around all kinds of obstacles. This ability is so sophisticated bats also use it to find food, even the tiniest of insects.

Bats have large, well-developed ears, too. A bat frequently can find a meal by listening for the sounds its prey makes.

One of the reasons I like bats in my garden is because they eat a lot of insects. They can eat as much as 25 percent of their weight in one feeding. That adds up.

Eleven species of bats are regular Pennsylvania residents, but not all of them are common, and three migrate to warmer climates in winter.

The little brown bat is the most common bat in the state. It, and its slightly larger cousin the big brown bat, are the bats you find most often in attics, barns and belfries, as well as in hollow trees or behind shingles and shutters.

The eastern pipistrelle, or pygmy bat, is less numerous than brown bats, but they are the bats most frequently found in caves. The pip and the rare small-footed bat-also called Leib’s bat-are contenders for the smallest bat. They only grow to about 3 inches long, with a wingspan of 8 to 10 inches.

The hoary bat, at nearly 6 inches long with a wingspan of up to 16 inches or so, is the largest bat you might see, but it is uncommon.

Most bats mate in late summer or fall, but female bats store the sperm in their reproductive systems until the next spring. At that time fertilization takes place and baby bats are born in the summer. Usually, bats only produce one baby a year, though the larger species can have up to four.

Come October and November, bats that hibernate here will be seeking adequate winter shelter again. Nearby, Laurel Caverns, the largest commercial cave in Pennsylvania, is a favorite winter destination for bats. Way down in the depths of the cave-beyond the normal route of guided tours-more than 1,800 were spotted in a count taken there in early 2005.

Bats are true hibernators. That means they don’t eat anything all winter. During hibernation their heartbeat, respiration and body temperature decreases, slowing their metabolism. They may move around a bit, but they can’t tolerate being disturbed too often-it just takes too much energy.

During spring, summer and fall, when they are out and about, bats sleep during the day, which is fine with me. It’s at the end of the day, when I finally sit down on the back patio to take it easy, that I appreciate watching their aerial acrobatics. And, as I pop two aspirin to soothe my tired muscles, you’re likely to hear me murmur, “I wish I could move like that.”

Susan Brimo-Cox gardens, observes nature and writes in Ohiopyle. Readers can send questions or comments to her at naturesgarden@brimo-cox-.com.