Grooming expresses harderian gland materials in the blind mole rat

The blind mole rat (Spalax ehrenbergi) is a highly aggressive and solitary rodent that shows the most striking physiological and behavioral adaptations to underground life. The eyes are not detectable externally; they are atrophied and covered by a thick layer of skin. A considerable part of the orbit is occupied by a very large Harderian gland. The current study demonstrates that during autogrooming the mole rat expresses Harderian gland materials from the conjunctival sac to the external nares and spreads them onto the fur. In contrast to other rodents, the mole rat's grooming behavior is usually confined to the front part of the body and does not progress after the head wipes to ventrolateral torso licking. Moreover, in highly aggressive encounters grooming sometimes ceases after the second phase‐the nose wipe bouts. The unique first phase of the mole rat's grooming consists of highly rapid strokes over the skinny border of the head, which we assume help to squeeze Harderian materials from the gland. Unlike other rodents, in which grooming occupies a considerable part of their waking time, mole rats, cage individually, rarely perform autogrooming behavior. Grooming in mole rats has been found to be highly correlated with aggressive encounters, and submissive animals exhibit significantly more grooming than their dominant opponents. It is speculated that the Harderian gland discharge may serve as an appeasing substance when mole rats meet to reduce the extreme aggressiveness typical of these subterranean rodents. © 1995 Wiley‐Liss, Inc.