Caste-specific techniques of defense in the polymorphic ant Pheidole embolopyx (Hymenoptera: Formicidae)

1. The queen of the Brazilian species Pheidole embolopyx is unique among ants in possessing a posteriorly truncated abdomen; in addition, the rear surface is clothed in unusual, hook-shaped hairs (fig. 1-3). Contrary to expectation, however, our studies have shown that the queen does not use the abdomen to block nest entrances or otherwise to oppose opponents directly. 2. The queen is also unique in possessing gelatinous sheaths on the scapes, anterior clypeal border, and frontal carinae. The sheaths vary in size and shape among queens and on the same queen with time (fig. 4), and they are often absent altogether. These unusual structures seem to be neither especially attractive nor repellent to the P. embolopyx workers. 3. We offer a different explanation of the queen's modified anatomy. The truncation of the abdomen and gelatinous sheaths are associated with flange-like protrusions of the pronotum and first gastric segment in an overall "chelonian" (turle-like) body form. The most vulnerable parts of the body are thus better protected from biting attacks, especially when the queen hides in tight spaces. But the meaning of this peculiar syndrome remains unknown. We believe it unlikely, for example, that the queen is a temporary social parasite. 4. Minor and major woerkers display different responses during recruitment and alarmdefense of the nest and food sources. These caste-specific behaviors are nevertheless coordinated to create efficient group-level reactions. Only the minor workers lay odor trails, which originate from the poison gland. Both castes cooperate in defending food finds, in the form of encircling clusters that persist for hours or even days. The minor workers seize the legs of intruding ants, while the majors attack their bodies directly. Both castes communicate alarm by means of abdominal pheromones, which in the case of the major worker has been pinpointed to the pygidial gland.