Wildlife Survey & Photo Service
Glossosoma, the Tortoise-shell or Saddlecase caddisfly, is rather common in California. In Putah Creek, there are two distinctive populations that overlap throughout the year. The larvae protect themselves from fish by building dome-shaped rock cases from which they can move freely and graze on algae. They do come out of the case and in some instances will drift in the water column. When they pupate, the larvae will typically congregate on the leeward side - or other protected area - and form a pupal case where they will mature for about 30 days. When the metamorphosis is complete, the pre-adults will chew their way out of the case, swim to the surface, and emerge as an adult.
Note the two sizes of larvae that grow and emerge at different times of the year. Because they have NO gills for "breathing" Glossosoma tend to prefer fast, clean, well oxygenated water.
Image on left shows two pupa encased in a rock case. The pupae were removed from the rock, flipped over and photographed.
An "emerger" is the adult stage which has the pupal case and pupal sheath, moved to the water surface. This is a highly vulnerable period as the emergers are subject to feeding trout. At the surface, the adult leaves the water to search for mates
Adult Glossosoma emerge sporadically throughout the year. I have confirmed that using yellow sticky traps that attract the adults. Most emerge in Spring and Fall months. Pregnant females enter the water to lay their eggs on the creek bottom. When the egg laying is complete, some females swim to the surface and fly away, others float downstream providing a morsel for foraging trout.
Please return for a suggested Glossosoma pattern.
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