glossosomatid larvae, unlike other related families within spicipalpia, build cases during the larva's first instar and each time the larva outgrows the case. cases are formed from large and small pebbles found within streams; these pebbles are spliced together with pieces of silk created by the larva. the case is formed loosely so as to allow water, and dissolved oxygen, to flow freely into the case for larval respiration. there are a couple of reasons why larvae produce cases: