Parthenogenesis is a type of reproduction in which a new organism develops from an egg which has not united with a sperm. In animals, it occurs naturally in rotifers, a type of worm, in BEES and APHIDS, and in water fleas. Some algae and fungi also reproduce parthenogenetically. Eggs of many invertebrates and of frogs have been developed without fertilization through artificial stimulation of the eggs by pricking, shaking, and changing the kind of solution they are in. Occasionally parthenogenesis occurs naturally in all major groups of animals except the vertebrates and echinoderms and in all plants except mosses and liverworts.
Parthenogenesis is the sole means of reproduction only in a few aphids and parasitic insects. In other groups males are produced periodically, usually in the fall. They fertilize eggs which are capable of surviving the winter. These eggs in turn produce females which reproduce parthenogenetic females until the next fall.