Fig. 4. Trajectories of wild-type worms on different bacterial food sources. (A) on Comamonas, (B) on E. coli HB101, (C) on E. coli DA837 and (D) on Bacillus megaterium. A single L1 larva was placed on a roughly rectangular bacterial lawn, and its movement trajectory during the subsequent 10-15 h was recorded. (Here, trajectories during the interval from 2-10 h of the experiment are shown.) The width of the field of view is approximately 10.3 mm; the bacterial lawn fits into the video field. The trajectory on B. megaterium is fragmented because of poor contrast; this problem was most severe at the edges, where bacteria tended to be the thickest. Roaming periods are shown in blue, dwelling in orange; there was much more roaming on mediocre food. Note that, since by definition the worms move slowly or not at all during dwelling, the extent of the orange traces doesn't reflect the proportion of time spent dwelling. (E) Sample speed of locomotion and turning angle (direction of movement change) traces of the wild type on E. coli foods HB101 and DA837. Roaming periods (green bars), when the turning angle stays low and the speed is high, are common on mediocre food, E. coli DA837, but very rare on good food, E. coli HB101. (F) Speed of locomotion and (G) movement duration distributions. On mediocre foods, the speed of locomotion and the movement duration is increased. In F and G, data from 10 worms on E. coli DA837, 11 on E. coli HB101, eight on Comamonas sp. and five on B. megaterium were averaged; trajectories in the interval from 2 to 10 h from the start of the recording were analyzed for each animal. Data are expressed as mean ± s.e.m. between individual animals. In G, error bars for E. coli foods only are shown. Because the trajectory on B. megaterium is fragmented (D), the population of long events is artificially decreased. The increased roaming duration on B. megaterium is still obvious, but the real effect is even bigger, as suggested by the speed analysis (F).