The Hackberry is host to a number of butterfly species, including the Hackberry Emperor (Asterocampa celtis). This butterfly will feed on the decaying berries in the late summer and fall, then make a winter nest by 'sewing' the leaves together around itself. In the spring, it will crawl out and start dining on the fresh leaves.
The Hackberry is also used by a number of other invertebrate and vertebrate species, being a central part of the Midwestern ecosystem. It's a nice tree to have in your woodland.