A SPRING FLING: FECAL FIRING IN FIERY SKIPPER CATERPILLARS (HYLEPHILA PHYLEUS)

Every living thing must dispose of waste. Successful waste removal includes not just clearing waste from body tissues, but also relocating it away from the organism to prevent disease or the attraction of other harmful species. This process can pose a challenge for relatively stationary species. Caterpillars in the family Hesperiidae build shelters from leaves or grasses in which they hide while feeding. To avoid the accumulation of feces, these shelter-building caterpillars fling their feces at high velocity, relocating the fecal matter away from the shelter. Here we examine fecal flinging in the fiery skipper (Hylephila phyleus) across a range of sizes (3 – 31 mm) representing five instars of development. We recorded highspeed video of fecal firing and calculated fecal takeoff velocity from caterpillars at each size. There was no effect of body size on velocity (average 0.62 ms-1). Size-independent velocity suggests the use of a latch-mediated, spring actuated mechanism, which has not yet been described in this species. We recorded additional highspeed video using a microscope lens to observe further details of the fecal firing mechanism. From these observations, we propose a mechanism whereby the movement of the anus and digestive tract deform an elastic cuticular structure, the anal comb, storing potential energy. When released, the anal comb rapidly recoils against the fecal pellet, launching it away at high velocity. These features support the hypothesized mechanism of a latch-mediated, spring actuated system.