Larvae of Donaciinae live underwater in the sediment attached to plant roots. The larvae pupate there in a water-tight cocoon, which they build using a secretion that is produced by symbiotic bacteria. The bacteria are located in appendages of the foregut of the larvae; in (female) adults they colonize two out of the six Malpighian tubules.
references
Kleinschmidt & Kölsch (2011a).