Monday, March 26, 2018

A Tricky One: Moth vs Butterfly? (Article by Al Young and Lesley Beaton)

During the outing to Cunningham’s Gap on 04 March 2018 we saw a ‘butterfly’ flitting in the open area next to the rainforest at West Gap Creek picnic area. Al thought it was a White-banded Plane (Phaedyma shepherdi) but when it landed on a tree trunk Lesley said it was probably a day-flying moth because it perched with its head facing downwards which is typical of some day-flying moths. While it was perched Al took a photo (See below).
So after consulting ‘Dr Google’ we decided it was a Forest Day-moth (Cruria synopla). This species is black with white spots on the forewing and a pale-yellow bar across each hindwing, which certainly resembles a White-banded Plane (Phaedyma sheperdi) especially when in flight.
The Forest Day-moth closely resembles Donovan’s Day-moth (C. donovani) but the hindwing bar of the Forest Day-moth is yellower and less irregular (ragged). Also, the Forest Day-moth has a faint narrow pale line from the base to the middle of each forewing. Apparently, both of these species are widespread in eastern Queens-land.
So, what are the distinguishing features between a White-banded Plane butterfly and a Forest Day-moth? (See photos below).

  1. While in flight the hind wing bar of the White-banded Plane is white whereas the bar is quite yellow in the Forest Day-moth. Probably the most reliable distinguishing trait.
  2. The pattern of white spots in the forewings are somewhat different but only readily discernible when they are perched. 
  3. The Forest Day-moth will often perch with its head downwards, whereas butterflies generally perch with the head facing upwards. 

Information on Day-moth (Cruria) species courtesy of Coff’s Harbour Butterfly House.

Forest Day-moth (Cruria synopla) – Cunningham’s Gap
Donovan’s Day-moth (Cruria donovani)^^ – in normal resting position with head upwards; image not rotated
Donovan’s Day-moth (Cruria donovani)^^ – image rotated 180 degrees
(Photos by Al Young)

^^ Previously wrongly labelled as White-banded Plane (Phaedyma shepherdi), Corrected in January, 2019 by the authors.

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