The size-distance relationship in the wood ant Formica rufa

1. The size-distance relationship among honeydew-collecting foragers of the red wood ant Formica rufa was investigated. Within the colony territory, t he size (as measured by head width) and fresh weight of samples of foragers were determined for ants ascending and descending trees near, and farther from, the central nest mound. 2. The mean size of the ants was significantly higher at far trees than at near trees in six out of the seven colonies investigated, confirming the ge neral presence of the size-distance relationship. 3. In three colonies, a load-distance relationship was also found. For a gi ven head width, honeydew-carrying ants descending far trees were significan tly heavier than those descending near trees (i.e. they were carrying heavi er loads from trees farther away from the central nest mound). 4. This is the first time that both load-distance and size-distance relatio nships have been reported in foraging workers from the same ant colony. 5. The combined effects of these characteristics suggest that colony foragi ng efficiency is enhanced by far trees being visited by the larger workers that then return with heavier loads of honeydew.