The genus _Aphaenogaster_[69] and its immediate allies include the harvesting ants of Europe and North America: they form subterranean nests consisting of isolated chambers connected by galleries; some of the chambers are used as store-houses or granaries, considerable quantities of corn, grass, and other seeds being placed in them. _A. structor_ and _A. barbarus_ have been observed to do this in Southern Europe, by Lespès, Moggridge, and others. [Illustration: Fig. 70—_Aphaenogaster (Messor) barbarus._ Algeria. A, male; B, winged female; C, large worker or soldier; D, small worker. × 3/2.] In the deserts about Algeria and Tunis a harvesting ant, _Aphaenogaster (Messor) arenarius_, is an important creature: its subterranean dwellings are very extensive, and are placed at a depth of several feet from the surface. Entrance to these dwellings is obtained by small holes, which are the orifices of galleries many feet in length: the holes are surrounded by pellets of sand projecting somewhat above the general surface, and consequently making the places conspicuous. The subterranean works occupy an area of fifty or a hundred square yards excavated at a depth of three to six feet. In these immense nests there exists a form of worker, of very small size, that never comes to the surface.[70] _Pogonomyrmex barbatus_ and other species have been observed to do harvesting in North America. After the workers of _P. barbatus_ have taken the seeds into the nest they separate the husks and carry them out, depositing them on a heap or {165}kitchen-midden, formed near by. M‘Cook has witnessed and described the process of stripping the seeds. Certain genera—e.g. _Aphaenogaster_, _Pheidole_—exhibit great disparity in the forms of the workers, some of which are of size much superior to the others, and possess disproportionately large heads; these large individuals are found in the same nest as the smaller forms. All the intermediate forms may frequently be found, and at the same time, in the genus _Aphaenogaster_; but in _Pheidole_ intermediates are of the utmost rarity. The genus _Cremastogaster_ is remarkable on account of the shape of the hind body and its articulation, which give the abdomen the appearance of being put on upside down. This mode of articulation may allow the Insect to threaten its enemies when they are in front of it; but it is doubtful whether the _Cremastogaster_ possesses an effective sting. [Illustration: Fig. 71—_Cremastogaster tricolor_, worker. A, with abdomen extended; B, uplifted.]