The life history of these insects is very complex; the winter eggs or larvae lie dormant during the cold season in crevices on the trunks, or hidden underground on the roots of their host plants; but as the warm weather approaches they crawl up the trunks, cluster round the opening leaf buds, and sticking their sharp beaks into the tissue, suck up the sap. These give birth to living larvae which grow very rapidly, and in turn (though virgin females) bring forth fresh broods of live larvae that in the course of several generations develop two pairs of large transparent wings, and consist usually of both sexes, though in some species the males are wanting. The last generation fly away in swarms but before dying deposit eggs which carry on the cycle of their life into the next summer. The wingless forms are short, stout, rounded creatures with small, slightly lobed heads, and rather stout 3 to 7 jointed antennae; the legs are well-developed with two-jointed feet. The abdomen often swells out into a flask-like shape; it is furnished on the 5th segment with a pair of cylindrical tubes called siphons, through which it discharges a sweet secretion known as “honey dew”; this liquid is often ejected in such quantities on aphis-infested plants that it covers the foliage, and attracts the ants, which come and lick up the globules of honey-dew on the tips of the siphons, and even caress the aphis with their antennae; and therefore in popular works these insects are often described as “ants’ cows.” [Illustration: =Fig. 163.=--_Siphonophora rosae_ (Linn.). The Rose Aphis of the garden. 1, Rose buds infested with aphis; 2, larva; 3, winged female aphis. (“Agricultural Gazette,” N.S.W.)] [Illustration: =Fig. 164.=--_Aphis persicae-niger_ (Smith). The American Peach Aphis (introduced). (“Agricultural Gazette,” N.S.W.)] Among the introduced species common in Australia is the Cabbage Aphis, _Aphis brassicae_, a dull green insect covered with a floury exudation; it is one of the greatest pests that the cabbage-growers have to deal with, and is always most troublesome in dry weather. The Rose Aphis, _Siphonophora rosae_, is a pale green species appearing in the spring on the young buds of the roses, but seldom doing very serious damage. The Woolly Aphis, _Schizoneura lanigera_, common both on the roots and branches of apple trees, is found in most of our old orchards; the dull blue aphids cluster together in colonies with their beaks buried deeply in the bark, and the clusters become covered with a mass of soft white flocculent exudation, hiding them from view. From the irritation to the plant tissue caused by their presence large galls or excrescences appear all over the branches. The Peach Aphis, _A. persicae-niger_, is another common orchard pest which winters on the roots of the peach trees: in early summer they commence to spread, and if neglected do a great deal of damage to the leaf and flower buds.