Some geometrid larvae exhibit dimorphism in colour. Several interesting observations of this phenomenon were made during the study of larvae of the species, Semiothisa sexmaculata Pack., Dysmigia loricaria Evers., and Nepytia canosaria Wlk.

In these observations, certain points stand out. Although larvae of S. sexmaculata are always green until they reach the last instar, both brown and green phases occur in that stage. After the last larval moult, a transition period of approximately two days is required for larvae to acquire the colouring of the brown phase. On the other hand, specimens of D. loricaria may pass their entire larval period in either a brown or a green phase (as do the larvae of N. canosaria, descriptions of which may be found in Can. Ent. 75: 186-189) or they may change (as do some larvae of S. sexmaculata) from the green phase to the brown phase in the last larval instar. For Dysmigia larvae to undergo this transformation, approximately three days are required.