The small dotillid crab Ilyoplax pusilla builds an earthen structure, termed barricade, close to its neighbour's burrow. Barricades function for territorial defence by deterring invasion by neighbours. Comparison of the frequency of barricade building in the breeding season among 5 localities across the geographical range of I. pusilla, showed higher values at more northern localities. In two localities differing in the frequency of barricade building, the response of crabs to artificial barricades placed near their burrows was examined. The artificial barricade was less often broken and more often avoided in the locality with the higher frequency of barricades. These results suggest that the local difference in frequency of barricade building is correlated with a difference in how crabs respond to this earthen barrier.
