From the Greek word parthenos ("virgin") and genesis. Parthenogenesis is monoparental reproduction by an individual female. This method of reproduction is practised by many groups of living organisms, in particular angiosperms (flowering plants) and many taxons of animals. But it never (or almost never) constitutes the only method of reproduction. Among arthropods, parthenogenesis is practised by insects (especially bees and ants). Among annelids, some polychaetes and oligochaetes sometimes practice parthenogenesis. Other protostome marine animals also use this method (nemerteans, rotifers...). Parthenogenesis is rare among vertebrates. But it has been observed among fish and reptiles.
Parthenogenesis seems to be useful under particular conditions. Bees and ants use it to produce males. Many marine animals use it to accelerate population growth, in order to quickly colonise environments that are only temporarily favourable. Forms of resistance (eggs with thicker shells, for example) are then produced.