Broad patterns of speciation are correlated with the evolution of new silk proteins in spiders but not in the lepidoptera.

Silk synthesis is an ancestral character of both the Lepidoptera and the Araneae. Araneae evolution is marked by an increased commitment to a silk-producing physiology. At least three major Araneae speciation events are correlated with the evolution of new silk-producing glands and new silk proteins. In contrast, although 98% of the Lepidoptera produce silk, there appears to be no relationship between silk use, protein types, and species numbers. The differences in these two systems, both meeting a need to produce a large volume of protein, may reflect predictable resource availability to herbivorous Lepidoptera larvae but fluctuating resource availability to carnivorous spiders.