As we all know, nectar is the primary food eaten by ruby-throated hummingbirds. However, did you know that they also dine on tree sap and tiny invertebrates? It is true. In fact, small animals can make up ten percent of their diet. The list of diminutive animals ruby-throats prey on includes spiders, caterpillars and bees, mosquitoes, gnats, aphids and even fruit flies.