Food – In the U.S., bats mainly eat insects. Bats vary in size and flight type, which enables them as a group to eat a great variety of insects. Small bats eat smaller insects, while large bats eat larger insects. Bats that fly fast (such as Mexican free-tailed bats), eat flying insects in the open. Bats that fly slowly with great maneuverability (such as Townsend bats), eat insects that live in congested natural places, such as forests and low to vegetation. Some bats (including those Townsend bats) can even hover and pick food off of leaves or tree branches.
Most bats are generalists and will eat about anything they can catch that fits their size and jaw strength. Some bats will specialize in certain types of insects (though not to the exclusion of other insects), such as beetles (big brown bats love them) or moths (Mexican free-tailed bats are perfectly happy with a diet of moths). Bats that eat insects on the wing often go wherever clouds of emerging insects form.
There are a few bats in the Southwest that feed on flower nectar and pollen (and are important pollinators), a bat that eats scorpions, centipedes and large insects (pallid bat), and a couple of the bigger bats will eat small bats (of different species than their own).
Flying requires a lot of energy. Heart rates can reach 1000 beats a minute (compared to resting 400 beats a minute). Bats can eat over half their body weight in insects every night to fuel their bodies. Females with young need the most food to support both themselves and their babies.
Catching insects – Bats use their echolocation skills to find and track flying insects. When you see a photo of a bat with its mouth open, it is echolocating, not being fierce!
They rarely catch their prey with their mouths. That sort of flying precision would be difficult to support given the movement of both bats and insects. They usually corral the insects with their wings and tail membrane, then dip their heads down to grab the insect. Bats will eat the insects as they fly, but some bats that feed on larger prey, or prey with tough body parts like beetles, will typically land on a perch to eat.
Bats with very large ears and short, wide wings often grab insects that are sitting on leaves or branches. These bats will hover and even listen for the movement of their prey.
Some bats will land near prey they have located and catch it there on the ground, such as pallid bats and their prey, scorpions.