Problems in Identification: Similar Species Indistinguishable In Photographs

All of the major moth families contain species pairs or groups in which it is extremely difficult, even impossible, to distinguish individual species from photographs. In such cases it is necessary to depend on measurements, geographic location, examination of internal genitalia, or DNA "bar-coding." A few specific cases are illustrated further below. Shown here is one representative from each of three genera that are particularly vexing to photographers and collectors. All of these are in the family Geometridae.

Eupithecia -- John Davis
Hydriomena -- John Davis Macaria -- Robert Patterson
  2301 -- Dichomeris Species Group -- Dichomeris serrativittella grp.

In MONA Fascicle 7.1 (1986) Hodges described four new species out of material previously assigned to Dichomeris serrativittella (2301). The four new species are D. xanthoa, D. isa, D. simulata and D. imitata. In his description of the five species Hodges stresses that they are inseparable on external characters. The ranges of the five species are undoubtedly imperfectly known. However, Hodges records specimens known at the time that he wrote and four of the species appear to be midwestern to western, or southeastern, with only one species known from the northeast, including southern Ontario. Thus, D. isa may well be what Nolie Schneider photographed in suburban Ottawa, ON.

D. isa - Nolie Schneider
  3188-90 -- Epiblema Sp. Grp. -- E. discretivana-obfuscana-desertana
Tom Murray
Hugh McGuinness Robert Patterson Robert Patterson
  The Plume Moths -- Pterophoridae

The three moths shown below are listed on the plate for Pterophoridae as Sphenarches ontario, Geina periscelidactyla and Geina sheppardi. But in each case there is a notation pointing out two other species which might also be considered. Most of the Plume Moths can't be identified with certainty based on photographs. There are simply too many species that share coloration and pattern. Genitalia are the keys to solid IDs.

Dave Pelletier
Robert Patterson Nolie Schneider
  A Black-lettered Dart -- Xestia dolosa and Xestia c-nigrum

These two species are very difficult to identify in the absence of accurate measurments. Hugh McGuinness has culled from among many of his photographs examples that come closest to matching the descriptions given by Don Lafontaine in MONA fascicle 27.3 (1998).

[m.] - Xestia c-nigrum - 14-18 mm
[f.] - Xestia c-nigrum - 14-18 mm [m.] - Xestia dolosa - 18-24 mm [f.] - Xestia dolosa - 18-24 mm
  6740-44 -- Crocus Geometer Species Group -- Xanthotype sp.
David Silsbee

Rindge examined a total of 1,886 specimens (m=1441, f=445) and also made 261 genitalic dissections. "No one has found a reliable way to recognize the species as yet except by genitalia. The adults of all species in this genus are, for practical purposes, externally indistin-guishable from one another, as they are are almost identical in color, maculation, and size."

Notes such as this are far from uncommon in the literature and require us to consider in many cases not giving specific names to moths that we photograph. Identification to species group or genus level may be the best we can hope for.

Nolie Schneider

MothTalk/MothTalk009.htm -- 01/15/2007