The earliest animal-pollinated flowers were pollinated by insects such as big beetles, long before bees first appeared. Bees are different because they are "specialized" as pollination agents, with behavioral and physical modifications that make pollination easier. Bees are generally better at the task than other pollinating insects such as beetles, flies, butterflies and pollen wasps. The appearance of such floral specialists is believed to have driven the adaptive radiation of the angiosperms, and, in turn, the bees themselves.