Page:Popular Science Monthly Volume 54.djvu/83

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75
THE HERDS OF THE YELLOW ANT.
THE HERDS OF THE YELLOW ANT.
By JAMES WEIR, Jr., M. D.

AS far as my observations go, and they extend through a period of twenty years, the aphides which live on grapevines, and which are the peculiar cows of the common yellow ant (Lasius flavus) of our gardens, show many curious phases in their life history. Especially is this true of the manner in which they perpetuate their species.

If a colony of aphides be kept under observation during the summer, it will be noticed that several kinds of individuals arise within it. By far the largest number of the herd will be made up of the wingless agamic form—that is, of females which reproduce without mating. In the species under consideration the young (during the summer) are born alive, and do not come from eggs.

So rapid is the increase of these insects that overproduction would soon kill off the colony by starvation were it not held in check by the peculiar anatomical and physiological metamorphoses which make their appearance in the offspring from time to time. Every now and then young ones are born which, in the course of time, evolve two pairs of wings; these winged individuals (which are also females and agamic) abandon the colony and produce elsewhere, in turn, wingless and single-winged individuals. In autumn both males and females are born; these mate and the females lay eggs.

These creatures secrete a honeylike fluid which exudes from two tubelike teats on the back of the sixth abdominal segment. Ants are passionately fond of this honey-milk and jealously guard and protect the herds of aphidian cows which produce it. They can be seen at all hours of the day, busily engaged in milking their queer kine. They will gently stroke the aphides with their antennae, thus inducing a free flow of the nectar from the abdominal tubules. Calves effect a like result by nudging their mothers with their heads; the cows "give down" their milk when thus assaulted by the calves.

In autumn, as soon as ovipositing has begun, the ants gather the aphis eggs as fast as they are laid-and carry them into their nests. Here they remain, carefully guarded and protected by the ants, until they hatch out in the spring, when the young agamic females are carried out by their foster mothers and placed upon the tender grape shoots or buds. This year the ants brought out the young aphides, which formed the herds kept under observation this summer, on the 18th of March. On the 19th they carried them back into the nest; this occurred in the forenoon, when the sun was shining and the air was warm and balmy. About 12 m. it began to storm, and became