Johan Billen1, Fuminori Ito2, Benoit Thys1, and Bruno Gobin1. (1) Zoological Institute, University of Leuven, Naamsestraat 59, 3000 Leuven, Belgium, (2) Faculty of Agriculture, Kagawa University, Ikenobe, Miki, 761-0795, Japan
In the ant Amblyopone reclinata, single foragers can retrieve small prey items. When the prey is too big to be carried alone, however, a scout will paralyse the prey and quickly return to the nest to recruit nestmate workers. During this homebound journey, the scout deposits a trail pheromone from the footprint glands that are situated in the hindleg pretarsi. Recruited nestmates follow this trail to locate the prey, which is then dragged to the nest with joint forces. The footprint gland represents a glandular differentiation of the tegumental epidermis at the dorsal side of both hindleg pretarsi. The secretory epithelium displays basal invaginations and apical microvilli, and is covered by a cuticle with narrow pores, that allow transport of the secretory products to the outside. The dorsal position of the gland may seem unusual for depositing trail substances onto the substrate, but careful observation showed that trail-laying workers curved their hindleg pretarsi in a peculiar upside-down position when they touch the substrate. This behaviour explains how secretion from the dorsally located footprint gland can be deposited onto the substrate. The number of recruited nestmates is proportional to the size of the prey to be carried. By using mealworm larvae as prey object, and decoupling prey length and prey weight by removal of hemolymph, we could demonstrate that weight is the key factor in the determination of prey size. The scout worker probably assesses the prey’s weight during the brief struggle that goes along with the stinging process, although it remains as yet unknown how the scout can transmit this quantitative information to its nestmates when it returns to the nest.
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