| Burrowing is a difficult form of locomotion due to the abrasive, heterogeneous, and dense nature of many substrates. Despite the challenges, many vertebrates and invertebrates spanning multitudes of taxa and body sizes burrow in a variety of terrestrial and aquatic substrates. Unlike terrestrial burrowers and modern digging equipment, many invertebrate burrowers lack rigid elements, and instead possess a fluid-filled hydrostatic skeleton. Soft-bodied burrowing invertebrates range in size from several hundred micrometers in length (e.g. nematodes) to several meters in length (e.g. earthworms), and burrow in environments ranging from muds to sands to soils. However, relatively little of the burrowing literature available has focused the effect of size on burrowing mechanics, and it is possible that the physical characteristics of soil may impose size-dependent constraints on burrowers. My research has found significant changes in morphology, soil stiffness, and burrowing behavior in Lumbricus terrestris earthworms during ontogeny. My results suggest that many aspects of the hydrostatic skeleton may change shape during growth to compensate for the ecological context of the organism. Specifically, I found that soil stiffness and resistance may become a significant challenge for soft-bodied burrowers as they increase in size, and must strain a greater volume of soil in order to form a burrow. |
