Assessment strategy in male-male contests of the hermit crab Pagurus middendorffii

► Four pathways of phase transition were observed in male-male contests of P. middendorffii. ► Intruders with small body size gave up the contest without physical combat. ► The escalation duration was longer if contestants had similar major cheliped size. ► To assess RHP, contestants switch both assessment tactics and index of RHP.