George Chandler Whipple, Gordon Maskew Fair, & Melville Conley Whipple, The microscopy of drinking water, New York, John Wiley & Sons, 1927, p. 444.

The organisms attached themselves to the pipe by means of strong claws at the posterior end of their body and his this position fed on plankton carried past them. The caddis worms were the worst offenders as they increase their bulk by collecting about their bodies a larval case built of sand grains and organic…