Sienna: a brownish orange [brown ochre].
Sigmoid: shaped like the Greek letter sigma, or English S.
Signate -us: = with marks or spots; see notate.
Signature: a colored blotch of any size or shape.
Silaceous: = ochraceous.
Silk: the hardened salivary secretion of certain larvae, mainly of Lepidoptera. similar material is produced by anal glands of some larva in Neuroptera.
Silk-glands: a pair of modified salivary glands in certain larva, mostly of Lepidoptera that secrete a viscid fluid which, on contact with the air, hardens into a silken fibre.
Silvicolous: living in moist, shady woods.
Simple, Simplex: without process, armature, or appendage of any kind.
Simple eyes: = ocelli; q.v.