Copulatory plugs are frequently observed in insects, reptiles, some mammals, and spiders. Copulatory plugs are inserted immediately after a male copulates with a female, which reduce the possibility of fertilization by subsequent copulations from another male, by physically blocking the transfer of sperm. Bumblebee mating plugs, in addition to providing a physical barrier to further copulations, contain linoleic acid, which reduces re-mating tendencies of females. A species of Sonoran desert "Drosophila", "Drosophila mettleri", uses copulatory plugs to enable males to control the sperm reserve space females have available. This behavior ensures males with higher mating success at the expense of female control of sperm (sperm selection).