自然界中，很多动物有自己的“领土范围”，它们常常以某种特殊物质“圈地”，并会因为“领土之争”打得不可开交。那么，到处乱飞的苍蝇也有自己的“领空”吗？ 

    It depends on the species, but some flies are very territorial, said Louis N. Sorkin, an entomologist at the American Museum of Natural History. Others, like the tsetse(舌蝇，采采蝇) fly, are attracted to large dark objects to seek blood meals, and so may follow a potentially tasty passer-by. Human beings offer other attractants(引诱剂，引诱物) for insects, like warmth, moisture, scent and carbon dioxide. 

    Several fly species have landmark-based territoriality, especially for their mating swarms, and may return to the same tree by a lake year after year. Male Cuterebra(马蝇) flies, also called botflies, form mating groups on hilltops, waiting for interested females, a ritual called hilltopping. In some species there is lively competition among males to take and hold a prime site. 

    In one study, scientists observed male flies of the Leschenaultia adusta species on small trees and shrubs on the highest parts of a peak in Arizona, flying in and out from time to time. Typically, only one individual stayed on a given plant for more than an hour, apparently holding the fort. These site-faithful males constituted about a quarter of the group; more than half of them also returned to the same perch for two or more days. They sometimes engaged in elaborate chase sequences.