The biology of the limnephilid caddisfly Dicosmoecus gilvipes (Hagen) in Northern California and Oregon (USA) Streams

The limnephilid caddisfly Dicosmoecus gilvipies (Hagen) occurs in many streams of northwestern United States and British Columbia. Because of the large size of the fully grown larva, its synchronous emergence pattern, and its frequent imitation by fly-fishing anglers, D. gilvipes is one of the best known North American aquatic insects. Egg masses are found at the bases of Carex sedges. Cases of early larval instars are made of organic material and detritus; 3rd and 4th instars incorporate pebbles into cases. The 5th-instar case is made entirely of mineral material. Larvae can travel up to 25 m per day, and are predominantly scraper-grazers. Fifth instars attach their cases to the underside of boulders in mid-summer and remain dormant until pupation in autumn. All northern California populations known are univoltine. Adult females use sex pheromones to attract males; most males come to trapped females in the 1st hour after sunset. In laboratory studies, males and females fly during the mate attraction period but generally not at other times. Males but not females exhibit circadian rhythms that govern flight periodicity. In enclosures to study biotic interactions, the density of D. gilvipes larvae has a negative effect on the densities of sessile grazers. This species has been widely used in trophic and behavioral studies conducted in the laboratory and field, and may be a model organism for ecological studies of caddisflies and other benthic macroinvertebrates.

Movement patterns and foraging ecology of a stream caddisfly larva

The movement patterns and time–activity budgets of Dicosmoecus gilvipes were quantified from underwater observations of marked individuals in a northern California stream, during two studies in early and late June, 1977. Individuals traveled several metres per day. The only striking differences between the observed patterns of movement and those predicted from a random walk model are the following: (a) in both studies, large larvae moved significantly farther than small larvae; (b) in both studies, there is a pronounced diel rhythm to movement, with animals traveling faster during the day; (c) rates of travel in late June are ~3 times faster than those in early June. Since more than two-thirds of the total time–activity budget of these larval insects is dedicated to feeding, we suggest that the patterns of movement reported here largely reflect activities related to food acquisition. Several observations indicate that food is locally limiting and heterogeneously distributed across the stream bottom, thus requiring animals to move from patch to patch in order to meet their food requirements. Seasonal differences in rates of movement appear to result from phenological changes in the quantitative and qualitative food requirements of these stream insect grazers.