On the cracking surface of a rotting opuntia branch, a large male cactus fly (Odontoloxozus longicornis) is standing over two much smaller females who are ovipositing into a small crevice. Other males of varying sizes repeatedly approach the trio and are repelled by the guarding male. He briefly establishes genital contact with one of the females, and she resumes oviposition immediately after he withdraws his aedeagus. Tucson, Pima County, Arizona, USA. 16 November 2008.