Aphids feed on phloem sap; for safe disposal of sugary honeydew, adults may possess a hinged cauda associated with the anus but never a vasiform orifice. Each adult may have two pairs of membranous wings of unequal size (alate) or no wings (apterous). The hind legs are not adapted for jumping; adult alatae are the main dispersive stage. The tarsi are each two-segmented, with a double terminal claw. Reproduction is usually asexual, by parthenogenesis and live birth (virginopary), although in temperate regions special sexual morphs may develop to allow frost-hardy overwintering eggs to be produced; the eggs lack a peduncle and are laid on twigs near overwintering buds. There are three immature stages.