Good on you for documenting behavior! It's fun to sit and watch ants as they work. You may find this excerpt from the chapter on foraging behavior in The Ants by Bert Hölldobler and E.O. Wilson helpful in thinking about what you're seeing.
Foraging Strategies
The approximately 8,800 known ant species use a dazzling variety of procedures for the discovery and retrieval of food. Several authors have attempted classifications of this important category of behavior, including Oster and Wilson (1978), Passera (1984), and Moffett (1987b). We will provide a synthesis here of what we regard as the most useful elements of these schemes. The resulting classification breaks all of the phenomena into three categories: hunting (3 kinds), retrieving (4 kinds), and defense (4 kinds). The elements in each can be combined to form 3 × 4 × 4 = 48 possible three-state foraging techniques. This arrangement provides an informal and convenient framework for
the description of the behavior of individual species.
Hunting: (1) by solitary workers; (2) by solitary workers directed to specific trophophoric fields by trunk trails; or (3) by groups of workers searching in concert, in the manner of army ants.
Retrieving: (1) by solitary workers who return home on their own; (2) by individual workers who return home along persistent trunk trails; (3) by individual workers recruited to the food sites by scouts; or (4) by groups of workers who gang-carry the food items.
Defense: (1) by guard workers during hunting or (2) the absence of such defense; (3) by guard workers during harvesting and retrieval of food; or (4) the absence of such defense.
Although no complete accounting has been attempted across all of the ants, it is our impression that virtually all of the 48 possibilities in this broad space of foraging techniques are employed by one species or another. At one extreme are the completely solitary foragers, including scavengers and specialized predators in all subfamilies other than the army ants of the subfamilies Dorylinae and Ecitoninae. The workers hunt singly and retrieve food items entirely on their own. At the other extreme are the army and driver ants of the genera Eciton and Dorylus, who hunt in groups, often gang-retrieve large prey items, and deploy specialized guard workers along the perimeters of the foraging columns.
The total foraging strategy of an ant species often comprises two or more three-state techniques, each chosen according to the quality and nature of the food of the moment. For example, when the solitary foragers of Pogonomyrmex encounter a seed or dead insect small enough to be carried singly, they carry it home alone. When the object is too large to be transported by one ant, or there is a cluster of small food items, the worker lays a recruitment trail with secretions from her poison gland. When the food is persistent at a particular site, as is the case for a continuing seedfall, the ants deposit trunk trails with secretions that come at least in part from the Dufour’s gland (Hölldobler and Wilson, 1970; Hölldobler, 1971b; Hölldobler, 1976a). The minor workers of the Amazonian myrmicine Pheidole embolopyx also search in solitary fashion and single-load the small insects they encounter. When the food item is too large to move, the scouts recruit other minor and major workers from the nest. The majors spend most of their time carving up the insect and defending it from intruders, while the minors concentrate on drinking the hemolymph and carrying fragments back to the nest (Wilson and Hölldobler, 1985). Minor workers of very small Pheidole dentata colonies spend more time feeding away from the nest and transferring the food to nestmates within the nest, as well as less time recruiting, than do minor workers in larger colonies. Evidently the effort of a single worker can more nearly satisfy the requirements of the small colony (Burkhardt, 1983).
Recruitment thus permits a multiple strategy of foraging and permits the exploitation of a wider range of food items. When workers of Monomorium, Myrmica, Formica, and Lasius forage singly, prey size is positively correlated with worker size. Yet when cooperative foraging based on recruitment is used, the correspondence breaks down. The ants are able to handle items far larger than their individual size (Traniello, 1987a). Although the workers in Traniello’s study varied in fresh weight from 0.1 to 6.8 milligrams, their arthropod prey varied from 1 milligram to over 2 grams, a 2,000-fold range from the lightest to the heaviest.
