Terrestrial hermit crab with electronic payloads for opportunistic roaming environmental sensing†

We demonstrated the free roaming of a terrestrial hermit crab (Coenobita spp.) with a detachable harness accompanied by different payloads of sensors and electronics. The payloads tested are as follows: (i) an LED circuit with a switch, (ii) a solar-powered temperature and relative humidity sensor with wireless live data transmission, and (iii) a salt water sensing module for salt water detection. The acquired migratory data demonstrated that the hermit crab was able to map out the boundary between salt water and dry land in an arena, suggesting its applicability in monitoring coastal salt water ingress. Unlike conventional animal tagging, the harness conforms to the turbinate pattern of shells via twisting motion, and the hermit crab can jettison the harness and payload at will by changing shells. This study explores the possibility of having hermit crabs as partners to pick up and randomly deploy sensors for opportunistic data acquisition without human intervention. They could function as a self-sustained roaming platform for detachable electronics.