Investigations into the effect of temperature and seasonal changes on the food-transmission activities of three ant species (Formica polyctena, Lasius niger and Myrmica ruginodis) using radioactive P32were carried out at Bonn, West Germany, between May and July 1969. One donor ant fed on radioactive food was given to 20 hungry ones for 30 minutes at 15°, 20°, 25° and 30° C at constant humidity. It was observed that in May the three species behaved more or less the same, each being moderately active (see figure). In June, however, they began to differ greatly with F. polyctena being the most active (more than in May) followed by L. niger and M. ruginodis showing the least activity. This difference between species increased to a considerable magnitude in July with F. polyctena showing the greatest activity followed by L. niger and M. ruginodis being the least active.