The local angle at each of the 18 inner segments, θi, was defined as the angle between its two flanking segments, si−1 and si+1. (A) Body-bends propagating from the head (left arrow) to the tail (right arrow) during forward locomotion in a wild-type mid L4 larva. For the purpose of demonstration, the local angles of only eight segments along the body were plotted. The color map corresponds to angles from the most anterior (brown), through the middle (orange and yellow), to the most posterior (grey) body-regions. Each bend appears as a peak or a trough in the local angle. A successive bend is initiated at the head ∼4 s before its predecessor reaches the tail. (B) Angles at the same eight body segments during early L4 lethargus. When the animal is quiescent the local angles remain constant or relax slowly. (C) The fraction of time, calculated from a 10 min running window, that individual body segments (as denoted on the worm schematic) are quiescent. Body-segments that are further removed from the head of the animal exhibit more quiescence than more anterior segments, such that the overall quiescent behavior associated with L4 lethargus reflects the quiescence of the head and the neck. (D) The length of the body (top) and the mean angle along its midline between the mid L4 and mid young adult stages. Shaded area denotes the L4 lethargus period. The reduction in body-length during lethargus may be a signature of growth in the volume of the body at a time when expanding the surface area of the body is constrained. Panels (C and D) depict N = 37 animals, mean ± SEM. Standard errors are illustrated as shadowed areas surrounding the plotted averages.