This tiny butterfly, here perching on a blade of prairie grass along the wildflower trail, has two tiny tails visible on its hindwings.

Eastern-tailed blues are very common, being found in suburban areas as well.

Look for large groups of them "puddling" as they seek moisture and minerals from damp ground.

The related Karner blue butterfly, which is found sporadically in northeastern Illinois, is state and federally endangered.