Here is an example of Speyeria (fritillaries) unfed first instars.  After the caterpillars overwinter, place them on fresh cuttings of violets or pansies.  Other genera of butterflies that also winter as unfed first instars are Cercyonis and some Boloria spp.  Note:  Unfed first instars are difficult to overwinter because of how sensitive they are to desiccation and mold (lab problem).