Butterflies are popular. Their bright colors and big wings appeal even to people who don't usually like insects. All butterflies start out as leaf-munching larvae (caterpillars) which eventually pupate and turn into butterflies. This means that butterflies seek out host plants on which to lay their eggs so that their larvae have plenty of food. While many butterfly larvae can feed on oak trees, there are only a few that seek out oaks in particular.
There are several species of hairstreak butterflies that lay their eggs on oak trees. Hairstreak butterflies tend to be about the size of a quarter and gray to brown in color. Some have bright markings on the wings, and some are very colorful. Not all hairstreaks lay their eggs on oaks, but some of the more common are the Edwards hairstreak (Satyrium edwardsii), the banded hairstreak (Satyrium calanus), the Arizona hairstreak (Erora quaderna), and the oak hairstreak (Satyrium favonius).
Some duskywing butterflies have very specific requirements and will only lay their eggs on certain species of oak tree. As the name implies, duskywings are brownish butterflies that average about an inch and a half wingspan. The sleepy duskywing will only lay eggs on the bur oak (Quercus macrocarpa, U.S. Department of Agriculture plant hardiness zones 2 to 8) while the mournful duskywing will only lay on live oak (Quercus virginiana, USDA zones 7b to 10). Horace's and Juvenal's duskywings will use a variety of oak species.
There are two species of brushfoot butterflies that lay eggs on oaks. Brushfoots are the most diverse butterflies in the world. They can be identified by looking at the front legs, which are short and end in a bunch of brushy hairs. The California sister (Adelpha californica) uses many oaks but prefers the canyon live oak (Quercus chrysolepis, USDA zones 5a to 10a). The white admiral or red-spotted purple (Limenitis arthemis) isn't picky and will use any oak that it can find.
Trees to Attract Butterflies
When planting a butterfly garden, it is important to remember that while flowers will attract butterflies to feed, food isn't the only thing that they need. Host plants for their larva are just as important. Plenty of caterpillars will use oak for food. Good oaks to attract butterflies with are the white oak (Quercus alba, USDA zones 3 to 8), red oak (Quercus rubra, USDA zones 4-8), live oak (Quercus virginiana, USDA zones 7b to 10) and bur oak (Quercus macrocarpa, USDA zones 2 to 8).