During the mating season female anacondas release pheromones to attract males for breeding, which can result in polyandrous breeding balls; these breeding balls have been observed in E. murinus, E. notaeus, and E. deschauenseei, and likely also occur in E. beniensis.[24][25][26][27] In the green anaconda (E. murinus), up to 13 males have been observed in a breeding ball, which have been recorded to last two weeks on average.[24] In anaconda breeding balls, several males coil around one female and attempt to position themselves as close to her cloaca as possible where they use their pelvic spurs to "tickle" and encourage her to allow penetration.[24] Since there are often many males present and only one male can mate with the female at a time, the success of a male often depends on his persistence and endurance, because physical combat is not a part of the Eunectes mating ritual, apart from firmly pushing against other males in an attempt to secure the best position on the female.[24][25]