Many bat species take advantage of these structures as roosts. From beneath the ground to far above it, human construction spans valleys, roads, and waterways. Our ubiquitous bridges sometimes provide excellent roosts for dozens of bat species. In the United States, more than 25 state transportation departments report bats living in expansion joints under bridges. You may not always find the occupant you'd expect inside an animal's home.
Birds are also instrumental in providing bats with places to roost.
More than a thousand spiders may make their home in these intricate nests. The bats are well hidden in the cluster of leaves that form the central part of the web. It is suspected that woolly bats sometimes return the favor by inadvertently picking up spider hitchhikers, which colonize in new locations. With suction pads on their thumbs and feet, these bats are able to climb inside the hollow joints of the stems where they roost. Sometimes they must contend with other itinerant lodgers, including a particularly aggressive ant known to vigorously defend the nest.