Spatial fidelity and uniform exploration in the foraging behaviour of a giant predatory ant

Social organisms benefit from division of labour and collective behaviours. However, if individuals overlap widely in their efforts, these benefits may not be proportional to the number of individuals that take part in an activity. We examined foraging behaviour and route fidelity in colonies of the ant Dinoponera grandis (formerly Dinoponera australis), a large species with relatively few active foragers that lack nestmate recruitment and chemical trailing behaviour. For 12 colonies, we marked individual foragers and mapped their foraging routes to test the hypothesis that each ant specializes in a particular area around the nest and that this route fidelity increases the overall area covered by the colony. For each individual, we recorded the mean direction and duration of each foraging trip, foraging success and maximal distance from the nest. For each colony, we measured the number of workers and the total foraging area. Additionally, we measured Shannon's entropy to describe foraging behaviour structure of the colonies. Overall, we mapped 272 foraging routes from 95 different foragers. The total area used by each colony averaged 66.2 m². Within colonies, over 68% of foragers exhibited a high degree of route fidelity, with most foragers following different foraging directions. Most colonies had a high Shannon's entropy, suggesting an even exploration of the foraging territory. Our results suggest that D. grandis exhibit route fidelity and high entropy. This strategy likely increases foraging efficiency and search area and may be particularly important for species with relatively few foragers.