Abstract
Many ants can cooperatively transport large food items (either coordinated or uncoordinated during transportation), which can be rarely observed in other animals besides humans. Although these behaviors have been extensively investigated on horizontal surfaces, few studies dealt with food transport on vertical surfaces. The red imported fire ant, Solenopsis invicta Buren, is an invasive ant species that commonly forages on trees. Our studies showed that S. invicta used multiple strategies to transport food items on vertical surfaces (tree trunks). Small food items (1 × 1 × 1 mm sausage) were carried and transported by individual ants, and larger food items were either collectively and directly transported or cut collaboratively first and small particles were then transported individually or collectively. Competition and deadlocks were frequently observed during individual and collective transport respectively. During cutting, groups of ants tightly fixed the food on the tree trunks by holding the edges of the food item, while other ants cut the food into smaller particles. All food items and particles were moved downward. We investigated the effects of food placement (placed on a platform or fixed on tree trunk), food shape (cuboid or flattened), particle sizes (0.45–1, 1–2, 2–3, or 3–4 mm), and placement height (20, 80, or 150 cm) on the food transport on tree trunks. Our studies are the first to show how fire ants transport food on a vertical surface, and may provide insights into the development of novel fire ant baiting systems that can be placed on tree trunks.
Highlights
Many ants can cooperatively transport large food items, which can be rarely observed in other animals besides humans
Two complicated patterns were observed during the lifting-to-vertical phase for larger food items (3 × 3 × 1 mm, 5 × 5 × 1 mm, or 8 × 8 × 1 mm): (1) lifting and incline: a few ants first lifted one edge of the food item, some ants squeezed into the gap between the food and platform; as more ants crowded into the gap and pulled the edge of the food, they leaned the sausage on the tree trunk; and (2) erection: the food item was parallel and attached to the tree trunks (Fig. 2, Table 1)
The two patterns were observed during the lifting-to-vertical phase for almost all large food items (3 × 3 × 1 mm, 5 × 5 × 1 mm, and 8 × 8 × 1 mm) except in one trial (3 × 3 × 1 mm) in which the erection stage was not observed (Food was directly lifted and transported to the vertical surface by ants when it was inclined)
Summary
Many ants can cooperatively transport large food items (either coordinated or uncoordinated during transportation), which can be rarely observed in other animals besides humans These behaviors have been extensively investigated on horizontal surfaces, few studies dealt with food transport on vertical surfaces. Some aspects of foraging behaviors, such as the cooperative food transport (multiple individuals simultaneously moving large food items), are fairly common in ants but can be rarely observed in other animals besides humans[7,8]. Czaczkes and Ratnieks[7] reviewed cooperative transport by ants and defined two types of well-coordinated food transport: (1) encircling coordinated transport, and (2) forward-facing coordinated transport The former type can be observed in ants such as Leptogenys diminuta Smith, Pheidologeton diversus (Jerdon), Novomessor cockerelli (Andre), and some Pheidole species[9,10,11]. The cognition (i.e., memory and learning) of individuals may play a role in the recruitment and food transportation on trails[20,21]
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