• Aberration is a formal term given to non-typical variation and implies "error in natural pattern or coloration."
• Dimorphic means "two morphs or forms," and often, but not always, refers to males and females being different (sexual dimorphism).
• Melanism refers to partial or full replacement of normal coloration by dark gray or black.
• Seasonal Forms represent a type of dimorphism where early and late broods are differently colored or patterned.
  
  

Some dimorphic forms are recognized with formal names. The second photo of P. cymatophoroides is form 'expultrix'.

Sexes differ visibly in numerous species. In some only the antennae differ, males having more feathery ones.

Melanism can be partial or complete, melanics being darker than the norm. In some cases, as in the Hypagyrtis below, it is difficult to decide whether an unusual specimen is an aberration, melanic, or simply an extreme variation. Members of the genus Hypagyrtis are sometimes collectively called "Hypagyrtis Variants." There is a great deal of variation within species and overlap between species. Many specimens cannot be identified to species without genitalic examination.

Half-wing melanics are not rare in my yard, probably running to 10% of all P. titea that I see. The melanic Major Sallow came from my yard. It's the only member of the species that I have seen thus far. In the south this moth is green with well-defined black markings. Melanics are seen with increasing frequency to the northward, and Tony Thomas tells me he has seen nothing but melanics in New Brunswick. They are not totally black, but they don't show much if any green coloration.