The original habitat of the North American maggot fly, Rhagoletis pomonella, was native hawthorn trees. About 200 years ago, some populations colonized newly introduced apple trees. The two populations are still classified as subspecies, but sympatric speciation is under way. What has contributed to incipient speciation in the maggot fly? Because apples mature more quickly than hawthorn fruit, the apple-feeding flies have been selected for more rapid development. Apple maggot flies try to avoid mating with hawthorn maggot flies. Maggot flies that feed and lay eggs on apples have gradually become adapted to this fruit.