Glenognatha emertoni (Simon 1887) is a small haplogyne orb-weaver collected near streams and dry streambeds in southern Arizona whose habits are unknown. Field observations revealed that G. emertoni are commonly found in vegetation overhanging streams and, more rarely, under streamside rocks. Mating pairs were observed on or near adult female webs. Males lack mate-guarding behavior and leave the female immediately after copulation. To examine mating behavior in a controlled setting, juveniles and adults were collected from the field and maintained in the lab. Matings were arranged between wild-caught adults and also between laboratory-reared virgins in order to describe mating behavior and sperm release during copulation. Unlike most other orb-weaving spiders studied, the number of sperm released and overall duration of copulation are not influenced by female mating history in G. emertoni. Male G. emertoni release equivalent numbers of sperm to virgin and non-virgin females. Given this pattern of sperm release and the lack of mate-guarding behavior by males, sperm competition should be intense in this species. Based only on the numbers of sperm released by each male in the study, doubly-mated females would be expected to produce egg sacs of mixed paternity, if all else were equal.