Fig. 2. Trail running speed as a function of temperature at ant height in a foraging trail of the same Messor pergandei colony as in Fig. 1. Symbols as in Fig. 1. Testing the null hypothesis by ANCOVA (slopes equal) yielded P>0.1. The common slope is 0.241 cm s^–1 deg.^–1. Testing the null hypothesis (intercepts equal) yielded P=0.08. The common intercept is –2.34 cm s^–1. The negative intercept reflects departure, outside the foraging temperature window, from a linear model of running speed/temperature. This figure shows inbound speed (towards the colony), which was slightly (16%) faster and less variable than outbound speed, which also showed no E-day effect (see text).