Regulation of building unit size in the house building of the caddis larva Lepidostoma hirtum

When the normally staggered relationship between the four sides at the anterior house rim of Lepidostoma hirtum was removed by cutting all the sides level, larvae were found to replace panels so as to regain the stagger. This was achieved by cutting panel lengths over a greater size range than normal but keeping mean panel length the same. The length of an individual panel was shown to be influenced by the site it was to occupy. Panel width was found to be positively correlated with panel length. The only rule for positioning a panel was found to be that of fitting to the most posterior gap on the anterior house rim. The rate of panel replacement was found to be increased not only by increase in amount of house removed but also by cutting all sides level.