The “insulation” layer in the cocoons of Argiope aurantia (Araneae: Araneidae)

1. 1. The capacity of the flocculent silk “insulation” layer within the cocoons of A. aurantia to control fluctuations in internal temperature was examined in the laboratory and in the field. 2. 2. Results indicate that the cocoon buffers changes in ambient temperature. However, the flocculent layer plays no insulatory role; it is the outer cocoon cover and the air space it creates which apparently acts as insulation. 3. 3. The mass of eggs or spiderlings in the cocoon also contributes to thermal damping, and the combined effect of this mass and the cocoon provide a significant buffer against temperature fluctuations caused by short-term radiation loads. 4. 4. Control of absolute internal cocoon temperature is probably achieved through maternal positioning of the cocoon at the habitat or microhabitat level, and is probably most effective during the early part of the reproductive season when the ambient air temperature is high and insolation is most direct.