Common swifts are insectivorous, feeding solely on aerial insects and spiders that it gathers in its mouth as it glides through the air. The insects are gathered together inside the throat through the use of a product from the salivary glands, to form a food-ball or bolus. Apus apus is commonly attracted to swarms of insects, as it aides in the ease of collecting sufficient food. It has been estimated that there are an average of 300 insects per bolus, and that each nest of young may receive 3000 food-balls per day. These numbers may vary based upon the abundance of prey. Among some of the most commonly consumed insects are aphids (Hemiptera), wasps, bees, and ants (Hymenoptera), beetles (Coleoptera), and flies (Diptera).
Animal Foods: insects; terrestrial non-insect arthropods
Primary Diet: carnivore (Insectivore )
This feeding statistic is a bit suspiscous. Concidered that average mosquito weights 2 mg, one bolus weights 600 mg (0,6 g). So, 3000 boluses per day per nest is 1,8 kg. That's a lot :) Deliver of food per chick is around 4-9 g per day, according to this article - Brood Reduction in Response to Manipulated Brood Sizes in the Common Swift (Apus apus), Thaís L. F. Martins and Jonathan Wright Behavioral Ecology and Sociobiology , Vol. 32, No. 1 (1993) , pp. 61-70.