Group Foraging

Fedoseeva (2015) - Group foraging of ants includes some distinct consecutive stages: mobilization, stream formation, and transportation of prey (Dlussky, 1981a). The behavior of individual ants during group foraging can hardly be described as uniform. For example, “scouts” of Messor ants determine the vector of movement toward the ripe seeds at the initial stages of stream formation but then prefer to act independently. In their turn, “passive foragers” turn back when they find themselves at the head of the column without a leader; but in doing so, they become reference objects for the outbound ants, which unintentionally keep the movement vector and gradually extend the path (Dlussky, 1981b). Thus, although individual actions not necessarily agree with the common vector, they contribute to the process as a whole. The general picture reflects the dualism of a social individual: it remains separate but is at the same time included in the common process by playing various roles and performing certain tasks.

Dlussky's four stages (preliminary activation (hereinafter, Activation), mobilization, transportation, and saturation) should have a fifth, Scouting. Scouting is characterized by uncoordinated behavior of foragers in the territory and the absence of the common response of the colony to their arrival in the nest. Activation differs from Scouting in that it involves a burst of activity in the nest in response to the arrival of a forager from the arena. This phase usually starts with the first act of trophallaxis performed by the forager, during which the acceptor stridulates, and during the subsequent food exchanges both the donors and the acceptors stridulate (Zhantiev and Sulkhanov, 1977; Dlussky et al., 1978). Correspondingly, the number of stridulating ants grows. At a high level of excitation, the scout performs the forager activation complex (FAC) that includes stridulation and exchange of strokes with antennae; sometimes other ants which have contacted the scout also perform the same complex. The signal is thus enhanced and spread over the colony, which is manifested by intensification of various intra-nest activities. If the colony has been without food for a long time, numerous foragers concentrate near the exit, and the very appearance of an ant with food triggers their emergence (Dlussky, 1981a).

According to Dlussky’s interpretation of mobilization as a process by which the detection zone is reached, it would be more precise to call the next phase of foraging by its purpose, i.e., Targeting. The growth in the number of workers in the near-nest area indicates transition from Activation to Targeting. Further development of the process becomes possible if the ants gathered near the nest exit proceed onto the outer territory in any pattern: independently, following the trail, and/or following the trail-laying “leader.” Thus, the appearance of ants moving along the trail or following the “leader” also indicates the possible beginning of a new phase. The increasing rate of emergence from the nest reflects the development of this phase, and an abrupt increase in the number of ants reaching the food source signals successful completion of Targeting. In the contrary case, the development of the process stops and can be resumed only by repeated excitation by new ants returning to the nest with food; in other words, the Activation phase continues.

The criterion of transition to the next phase, Transportation, is the establishment of a stream of ants leaving the target for the nest, which is preceded by the growth of the number of workers in the target zone. The essential difference between this phase and the preceding one is that in the Transportation phase the forages arriving at the target meet those leaving it. The phase of Saturation starts when the two streams become leveled in intensity.