Problems in Identification: Aberrants, Dimorphics, Melanics and Seasonal Forms


  • 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.

  Aberrations: Joyful Holomelina Moth -- Holomelina laeta

    In addition to offering examples of aberrations this species is sexually dimorphic.
 
typical male typical female aberration 1 aberration 2 aberration 3

This row shows sexual dimorphic difference as well as aberrations that might be encountered in a species. Aberrations are not seasonal forms but occur more or less randomly, or at differing rates of frequency.

These specimens were all taken in Louisiana by Vernon A. Brou, Jr.

  Dimorphism -- Neither Seasonal nor Sexual


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

Tufted Thyatirid Moth -- Pseudothyatira cymatophorides
Robert Patterson - MD

Rose Hooktip Moth -- Oreta rosea
Robert Patterson - MD

Palmerworm M. - Dichomeris ligulella
Robert Patterson - MD

Lunate Zale Moth -- Zale lunata
Troy Barlett - GA

Lunate Zale Moth -- form 'edusa'
Machele White - FL

  Dimorphism -- Sexually Distinctive Species


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

male -- Io Moth -- Automeris io -- female
Robert Patterson - MD

male -- Ambiguous Moth -- Lascoria ambigualis -- female
Robert Patterson - MD

male -- Red-banded Leafroller Moth -- Argyrotaenia velutinana -- female
Robert Patterson - MD

male -- Peachtree Borer Moth -- Synanthedon exitiosa -- female
Patrick Coin -- NC                         Richard Leung - VA

  Melanism


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.

One-spotted Variant Moth - Hypagyrtis unipunctata
Robert Patterson - MD

Melanic-Aberrant Hypagyrtis unipunctata ??
Jane and John Balaban - IL
Esther Moth - Hypagyrtis esther
Robert Patterson - MD

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.

The Half-wing Moth - Phigalia titea
Robert Patterson - MD

The Half-wing Moth - typical
Robert Patterson - MD
Major Sallow Moth - Feralia major
Larry Line - MD
  Seasonal Forms
Red-fringed Emerald Moth -- Nemoria bistriaria
Spring form -- Arlene Ripley - MD

Red-fringed Emerald Moth -- Nemoria bistriaria
Summer form -- Larry Line - MD

Many instances of seasonal form exist that are much more subtle than those shown here. Spring broods may be duller while summer broods are brighter, one may have weaker markings and the other bolder. In the Variable Antepione there is both seasonal and sexual dimorphism as well as variation in markings. It's a very complex situation.

The phenomenon of dimporphic broods is thought to reflect temperature differences during egg, and perhaps larval, development. There is also some evidence that, in lepidoptera, temperature during development can influence sex ratios within a clutch or brood. Covell reports that all forms of Antepione thisoria were found within a single brood reared in Nova Scotia.

Variable Antepione Moth -- Antepione thisoaria
Spring form -- Robin McLeod - ON

Variable Antepione Moth -- Antepione thisoaria
male Summer form -- Larry Line - MD

Variable Antepione Moth -- Antepione thisoaria
female Summer form -- Larry Line - MD







MothTalk/MothTalk011.htm -- 01/15/2007