Life History.

The perfect insect, the winged viviparous female, is quite black, of a somewhat shiny appearance. The male, which has wings, is also black.

Both larvæ—wingless viviparous females—and pupæ are at first of a lighter colour, but they soon become black.

At the end of the summer, or when the food supply has ceased, the generations of aphides are produced with wings and fly away to their winter retreats. Here they deposit wingless females, which lay eggs upon the leaves and in the axils of the leaves of the dock, broom, furze, thistle, borage, and other common plants, to be hatched out in the spring. From these eggs larvæ are hatched. These produce living larvæ endued with the power of reproducing living scions for several generations without coition. This parthenogenetic reproduction is continued for several generations. But when food fails, or is not appreciated, generations intervene having wings to carry them to fresh and more congenial plants. It appears that bean plants afford especially grateful food for these aphides, because in favourable circumstances they increase upon them with marvellous rapidity and soon ruin the crop; whereas upon their normal hosts—docks, thistles, broom, furze, and others—their ravages are seldom appreciable.