TRAIL LAYING BEHAVIOR DURING FOOD RECRUITMENT IN THE ANT LASIUS-NIGER(L)

The trail-laying behaviour of foragers of the ant Lasius niger was obs erved in the laboratory on a 20 cin bridge between the nest and the fo od source. We measured both the frequency of trail laying, as defined by the proportion of trips during which trail laying occurred, and its intensity, as defined by the number of marks laid during one bridge c rossing. Foragers do not exhibit trail-laying behaviour until a food s ource is discovered. Trail laying then occurs more or less equally bot h to and from the nest, and both its frequency and intensity decrease as the recruitment proceeds. Foragers from very small colonies less th an a year old appear to have quantitatively the same trail laying beha viour as those from older and much larger colonies. Groups of recruite rs and recruits were individually marked. Their trail laying intensity was similar, both for trips to and from the nest, and for an ant's fi rst, second, third and fourth trip. The frequency diminished rapidly w ith the number of trips made by each individual, and was 2-3 times hig her for recruiters than for recruits, for trips both to and from the n est. Even though foragers stop marking after a variable number of pass ages, they continue to move between the nest and the food source, and other ants start marking. Different foragers appear to have widely dif ferent levels of trail laying, although we cannot say whether these di fferences are stable between different recruitments. Trail laying is s trongly affected by the foragers' position on the bridge, especially f or ants returning to the nest which lay up to five times more on the s egment closest to the source than that closest to the nest. Foragers o n a weakly marked trail appear to mark more than those on a well-marke d trail. However, this effect is weak and could partly be attributed t o their lower speed. Finally, a model using the experimental data gath ered on the individuals' trail-laying behaviour reproduced satisfactor ily the colony's overall trail laying.