Facultative parthenogenesis is the term for when a female can produce offspring either sexually or via asexual reproduction. Facultative parthenogenesis is extremely rare in nature, with only a few examples of animal taxa capable of facultative parthenogenesis. One of the best-known examples of taxa exhibiting facultative parthenogenesis are mayflies; presumably, this is the default reproductive mode of all species in this insect order. Facultative parthenogenesis is believed to be a response to a lack of a viable male. A female may undergo facultative parthenogenesis if a male is absent from the habitat or if it is unable to produce viable offspring.