Tidepool Tim says,  “Of all the hermit crabs (Pagarus spp.) we catch over the course of a year about 1 in 50 will have a dense pinkish colony of these hydroids covering their shells. We have not noticed any particular collecting area that has a higher incidence of them. Once in our holding tanks - it does not seem to spread to other hermits either. These hydroids are very small and not very noticeable other than the pink sheen they put on the shell. Fun to add a moving sideshow to your aquarium. We sometimes do see hermits with a good coating of obelia hydroids as well.”