Hummers eat most any soft-bodied bugs they can swallow whole: fruitflies, gnats, aphids, and tiny spiders, plus their eggs and larvae. If you have an insecticide-free lawn and garden, you'll have plenty of bugs to fuel hummingbird migration.
"The two hummers in my yard are almost exclusively bugging now. They rarely come to feeders except early morning and late afternoon. I expect they'll leave soon," reported Meret Wilson in Ormond Beach, Florida. 03/14/16