Insect. Soc. 53 (2006) 46–55 0020-1812/06/010046-10 DOI 10.1007/s00040-005-0834-9 © Birkhäuser Verlag, Basel, 2006 Insectes Sociaux Research article How does food distance influence foraging in the ant Lasius niger: the importance of home-range marking C. Devigne and C. Detrain Service d’Ecologie Sociale CP. 231, Université Libre de Bruxelles, Campus Plaine, Boulevard du Triomphe, 1050 Brussels, Belgium, e-mail: cdricdevigne@yahoo.fr, cdetrain@ulb.ac.be Received 13 July 2004; revised 26 January and 20 May 2005; accepted 2 July 2005. Abstract. We study the influence of food distance on the individual foraging behaviour of Lasius niger scouts and we investigate which cue they use to assess their distance from the nest and accordingly tune their recruiting behaviour. Globally, the number of U-turns made by scouts increases with distance resulting in longer travel times and duration of the foraging cycle. However, over familiar areas, home- range marking reduces the frequency and thereby the impact of U-turns on foraging times leading to a quicker exploita- tion of food sources than over unmarked set-ups. Regarding information transfer, the intensity of the recruitment trail reaching the nest decreases with increasing food distance for all set-ups and is even more reduced in the absence of home- range marking. Hence, the probability of a scout continuing to lay a trail changes along the homeward journey but in a different way according to home-range marking. Over unex- plored setups, at a given distance from the food source, the percentage of returning trail-laying ants remains unchanged for all tested nest-feeder distances. Hence, the tuning of the trail recruiting signal by scouts was not influenced by an odometric estimate of the distance already travelled by the ants during their outward journey to the food. By contrast, over previously explored set-ups, a distance-related factor – that is the intensity of home-range marking – strongly influ- ences their recruiting behaviour. In fact, over a home-range marked bridge, the probability of returning ants maintaining their trail-laying behaviour increases with decreasing food distance while the gradient of home-range marks even in- duces ants which have stopped laying a trail to resume this behaviour in the nest vicinity. We suggest that home-range marking laid passively by walk- ing ants is a relevant cue for scouts to indirectly assess dis- tance from the nest but also local activity level or foraging risks in order to adaptively tune trail recruitment and colony foraging dynamics. Keywords: Distance assessment, foraging distance, home- range marking, Lasius niger. Introduction In order to make adapted individual decisions, foragers have to assess information about characteristics of food sources and the environment. Instead of making a complex assess- ment of all factors, they can utilize cues with a highly reliable and functional informative content (Detrain and Deneu- bourg, 1997, 2002). Several studies investigated how mass- recruiting ants tune their foraging and trail-laying behaviour mainly according to food characteristics (in Lasius niger, food quality: Beckers et al., 1993; food volume: Mailleux et al., 2000; food type: Portha et al., 2002; Le Breton and Four- cassié, 2004 or food weight in Lasius neoniger, Traniello, 1983; for a review see also Detrain et al., 1999a) but to a less extent according to environmental factors such as food dis- tance. Concerning food distance, most authors who aimed at testing optimal foraging predictions, have examined how distance influences foraging strategies in terms of time/ energy costs and gains for ant colonies. Relationships be- tween increasing food distance and larger forager body sizes or heavier food loads were reported in fungus-growing (Roces, 1990; Wetterer, 1991; Roschard and Roces, 2003a), harvester (Nonacs, 2002) or honeydew collecting ant species (McIver and Loomis, 1993; Wright et al., 2000; Nonacs, 2002). There is also evidence that distance of food patches determines task partitioning, sequential load transport (An- derson et al., 2002; Roschard and Roces, 2003b) and size- matching (Ferster and Traniello, 1995; Roschard and Roces, 2003b). As regards food exploitation dynamics, distance acts upon the timing and/or intensity of nestmates recruitment to a foraging place (e.g. in Paraponera clavata (Fewell et al.,