Abstract
The intertidal ocypodid crab Ilyoplax pusilla builds a mound at the burrow entrance, by piling mud excavated from the burrow or gathered from the nearby surface. Mounds located separate from the burrow entrance were built predominantly by hard carapace males, while mounds adjoining or enclosing burrow entrances were mainly built by ovigerous females and heterosexual pairs. During heavy rain, when surface activity was lowered, the proportion of burrows with a separate mound decreased whereas that of burrows with a mound adjoining the burrow entrance increased. Females with a mound adjoining the burrow entrance showed shorter surface activity, compared with females without a mound. Between males with a separate mound and males without a mound, the duration of surface activity was not different.
