The Briefly Colonial Life of Hatchlings of the Net-Spinning Caddisfly Plectrocnemia conspersa

Abstract

Egg masses of the European net-spinning caddisfly Plectrocnemia conspersa were collected from a small stream, with the object of studying egg incubation and early (first seven days) larval behaviour. Egg masses contained 150-800 eggs (mean 440.2, 95%CL 75.6). Egg incubation period in the laboratory (y days) was related to temperature (x°C) by the equation ln(y) = 3.14 + 0.144 ln(x), taking 93 days at 6°C and 20 days at 18°C. Egg masses incubated in the field hatched as predicted by this equation. The length of individual eggs increased by an average of 17% during incubation. Emergence from the egg took about 30 min, and newly hatched larvae had yolk in their guts which lasted 24-30 h, after which feeding began. Larvae took only live prey. In still water, larvae span silk, ventilated using abdominal undulations, turned in the net, and performed further miscellaneous movements. Newly hatched 'yolky' larvae spent the most time spinning; older larvae resident in the mass of silk near the maternal egg mass car...