Hummingbirds eat a combination of nectar from flowers and small flying insects. Nectar is the more widely known and understood hummingbird food. Scientists have noted that the shape of the birds' bills and tongues are highly adapted to reaching deep within the recesses of flowers to retrieve nectar. However, as nectar is poor in everything but calories, hummingbirds make up the nutritional deficit by consuming bugs.
Nectar is very sugary, which is vital, as it gives hummingbirds a rapid boost of energy. Hummingbird flight consumes a great deal of energy, they are warm-blooded and must burn calories to maintain that temperature, and their tiny bodies dissipate heat all too efficiently. All of these factors combine to make hummingbirds exhibit the highest metabolism of any animal outside insects. Nectar, however, lacks protein, fat, vitamins or minerals, so hummingbirds resort to predation. The favored prey of ruby-throated hummingbirds is spiders, making up 60 to 80 percent of their diet. Hummingbirds also consume beetles and parasitic wasps, along with pests such as mosquitoes, ants, flies, gnats, aphids and mites. Hummingbirds hunt in the manner of a flycatcher, a type of bird that captures insects in flight. They also take advantage of spider webs, and will often consume both a spider's prey and the spider itself.