The egg is generally upright with a broad base, rounded top and irregularly or regularly ribbed sides which are vertical or taper slightly upwards, or it may be reticulated with ridges and depressions. At the top there is a slight depression containing the micropyle (Common, 1990). The eggs are said to be laid singly but there are several references to larvae feeding communally.
The larvae have mouthparts directed ventrally or forward (for structural details see Common (1990), Kristensen (ed.) (1998) and Holloway et al. (2001)). Larvae have 'L' (for lateral) setae (Stehr, 1987), but only two on either side of all thoracic segments. The larvae are stout in the case of the Thyridinae and Striglininae but slender in the Siculodinae. Larval stages of the European species Thyris fenestrella Scopoli are detailed by Hasenfuss (1979, 1980).
The larvae are often stem borers (a similarity with pyralids) and many provoke galls or feed gregariously, externally on webbed fruit or leaves or in rolled or folded leaf shelters. Larval food plants are recorded from some 30 families, including prominently Capparaceae [Capparidaceae], Combretaceae, Dipterocarpaceae, Euphorbiaceae, Leguminosae, Myrtaceae, Piperaceae and Sapotaceae (Aiello, 1980; Li, 1996; Robinson et al., 2001) but few can be considered pest species of economic importance. Aiello (1980) described the egg, larva, pupa, and larval behaviour of Dysodia sica Druce reared on Barro Colorado Island, Panama and Sevastopulo, (unpubl. Ms in HOSTS), records a larva of Arniocera sp. (Charideinae) as feeding on Grewia (Tiliaceae).