The Blue-gray Gnatcatcher is a very small songbird. Adult males are blue-grey on the upperparts with white underparts and have a long slender bill, long black tail and an angry black unibrow. Females are less blue without the unibrow. Both sexes have a white eye ring.
Their breeding habitat includes open deciduous woods and shrublands in southern Ontario, the eastern and southwestern United States, and Mexico. They build a cup nest similar in construction to a hummingbird nest on a horizontal tree branch. Both parents construct the nest and feed the young; they may raise two broods in a season.
They forage actively in trees or shrubs, mainly eating insects, insect eggs and spiders. They may hover over foliage or fly to catch insects in flight.
The tail is often held upright while defending territory or searching for food.