Species in the genera Diadasia and Svastra are collectively called sunflower bees because, along with several other groups of plants, they are sunflower (Helianthus annuus) specialists. In addition to sunflowers, these bees specialize on mallows (Malvaceae), cacti (Cactaceae), evening primroses and willow herbs (Onagraceae), and wild bindweeds (Convolvulaceae). In fact, several cacti and mallows rely on sunflower bees for pollination services.

Diadasia species are restricted to the New World; most occur in the western United States, although some occur in Canada as well. Diadasia species are small to medium sized, ranging from 5 to 22 mm long. They are robust and hairy. Males have long antennae.