Christmas tree pests and weeds of different pests, most of which cause cosmetic damage to the trees, important in the Christmas tree industry. The balsam woolly adelgid ("Adelges picae") are small soft-bodied insects which attack the Fraser fir. The insects appear as white, woolly spots on the tree and are fatal to the fir if left untreated. The woolly adeligid was native to central Europe where it affected the silver fir; it was introduced to the United States, where it has no known native predators, before 1900. Balsam twig aphids ("Mindarus abietnus") are another type of tree pest which affects fir and spruce trees in
Medium tree finch same. This reflects the fact that the two species feed on the same type and size of insect. The beak of the medium tree finch is intermediate in size between the small tree finch and large tree finch. All three species are found in the same habitat. The medium tree finch is threatened by introduced predators such as rats, mice, cats, and the smooth-billed ani, as well as habitat loss, which has occurred through clearance for agriculture. The introduced fly "Philornis downsi" is a significant threat to the survival of this species. Parasitic larvae of this fly live in the