Page:Popular Science Monthly Volume 71.djvu/556

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THE researches of the past few years have materially changed our views on the significance and phylogenetic origin of the so-called slave-making instincts among ants. And although the subject still involves many unsolved problems, we are now in a position to look back on its history and marvel at our too implicit confidence in certain analogies, at our neglect of the basic principles of phylogenetics, and at the inept questions we so long persisted in asking.

Slavery, or dulosis, is a rare phenomenon among ants. In its pure form it is known to occur only in two of the several thousand described species, namely, in the sanguinary or blood-red slave-maker (Formica sanguinea) and the amazon (Polyergus rufescens). These species, with their various subspecies and varieties, are peculiar to the north temperate portions of Europe, Asia and America. The phenomenon was first discovered by J. Pierre Huber (1810)[1] and most completely described by him and by Forel (1874)[2] These investigators, of course, fixed their attention on the behavior of the workers. To this aspect of the subject later writers have added little of importance, and have merely fallen into a natural error of continuing in the same path as their illustrious predecessors. This was the case, for example, with Darwin[3] and with Wasmann, who for the past quarter of a century has been observing the slave-making ants of Europe. Huber and Forel showed that the workers of F. sanguinea and P. rufescens make periodical forays on colonies of ants belonging to the F. fusca group, carry home the worker cocoons and larvæ, and permit some of these to hatch and to survive with them in the same formicary. An eminently predatory species thus comes to live in intimate symbiosis with workers of an alien species which are said to function as slaves, or auxiliaries. F. sanguinea is a powerful and very plastic species which continues to exercise all the fundamental ant instincts in the presence of its slaves. It can excavate galleries in the soil, obtain its own food and bring up its own young. Polyergus, however, is abjectly dependent on its auxiliaries. It is no longer able to excavate a nest, care for its own

  1. "Récherches sur les mœurs des fourmis indigènes," Paris et Genève, 1810.
  2. "Les Fourmis de la Suisse," Zürich, 1874.
  3. "On the Origin of Species by Means of Natural Selection," third edition, London, John Murray, 1861, p. 244.