Food recruitment strategies of the ants Myrmica sabuleti and Myrmica ruginodis.

The food-gathering systems of Myrmica sabuleti and Myrmica ruginodis are analysed and compared to those, previously described, of M. rubra and M. scabrinodis. Workers of the two species studied in this paper collect pure water or small dead prey without actively recruiting congeners. Collecting ants of M. ruginodis lay down a trail pheromone from their poison gland only when returning to the nest, while foragers of M. sabuleti deposit a trail on their way both to the nest and back to the food but almost only in darkness. Collecting ants of both species are not followed by the few workers which, excited by them in the nest, individually reach the food. In the two species studied, an active recruitment of workers occurs when a large dead prey or a source of sugared water is presented to a colony. After having deposited their trail on their way to the nest, recruiting ants 'invite', by tactile signals, congeners to leave the nest. Then the recruiting ants return to the food, laying down their attractive Dufour's gland content along distances varying with the species and the food stimuli considered. Recruiting ants of M. ruginodis generally emit their Dufour's gland secretion along longer distances than M. sabuleti foragers, after which they secrete nothing more, while M. sabuleti workers go on their way to the food laying down their trail substance again. The food-gathering technique of the two species studied includes group recruitment, performed on longer distances in M. ruginodis than in M. sabuleti, followed by mass recruitment. The number of ants finally recruited onto food is generally excessive in M. ruginodis, and in M. sabuleti the site is only just saturated. A comparison of these food-collection techniques with those of different species of Myrmica, together with a chemical and an ethological study of these species' pheromones would provide information for a better understanding of these species' ecology, as well as taxonomic and phylogenetic positions.