Research is currently being pursued in shell selection by the hermit crab. Hermit crabs usually are found in empty gastropod shells, seeking protection from predators, desiccation, and other hermit crabs. The hermit crab does not seem to select a place to stay at random but rather appears to have a selection process. Precisely what this process is and how the crab makes a decision as to what shell to select and what shell to reject is the subject of much research.
Hermit crabs are considered ideal for research into decision making of this sort. When an animal stops performing one activity, it must decide what activity to perform next, and this is called a "decision point." At any time, causal factors for several different potential activities are likely present, and the question arises as to how the animal selects which activity to perform. Certain common sense answers suggest themselves. The causal factors may be "weighted" in terms of their consequences for the fitness of the animal and for the animal to select that activity for which the highest level of causal factors exists. Disinhibition may occur in times of conflict between tendencies toward two opposing behaviors, leading to displacement activities. Another approach is found in the state space model, which assumes that all activities are mutually exclusive and that each combination of causal factors will determine a particular activity (Elwood and Neil 15-17).
Hermit crabs lend themselves to this research. In most animals, assessments can only be inferred based on the decisions the animals make, but, with hermit crabs, the assessment procedure itself can be observed, the sequence of investigatory acts can be recorded, and the timing of decisions can be noted. The researcher can alter the shells so they convey different information to the animal, and then the consequences can be determined. Hermit crabs are known to fight over the ownership of shells, and m...