We are please to provide the following most interesting note on confused species and would like to thank the Huntingdonshire Moth & Butterfly Group and in particular, Barry Dickerson for allowing us to publish it here.

One would think that in these modern times identification of our macro moths would become easier, but it appears the opposite is happening. As recently as 2004 it was discovered that the notch near the costa on the inner line of the central band on the forewing of the Dark-barred Twin-spot Carpet (Xanthorhoe ferrugata) was not a reliable way to separate this species from the Red Twin-spot Carpet (Xanthorhoe spadicearia). There are other features which are less distinct mentioned in the books, but none of these has proved reliable particularly in worn specimens and to add to the confusion the Dark-barred Twin-spot Carpet has a red form, and the Red Twin-spot Carpet a dark form.

In 1984 it was discovered that the Common Rustic (Mesapamea secalis) was found to be two species and the following year it was split again. The new species, which are not possible to recognize from the Common Rustic without dissection, were named the Lesser Common Rustic (Mesapamea didyma) and Remm's Rustic (Mesapamea remmi).

The Uncertain (Hoplodrina alsines) and the Rustic (Hoplodrina blanda) form another pair, which are almost impossible to tell apart. The books give a list of differences, which in my experience are not always reliable. Another pair, which can often include a third, is the Minors, namely the Marbled Minor (Oligia strigilis) and the Tawny Marbled Minor (Oligia latruncula). The third species, the Rufous Minor (Oligia versicolor) can also be confused with the previous two particularly in dark and worn specimens. Again differences are mentioned in the books, but these are now being rejected, as they are unreliable.

A further group is the November Moths (Epirrita dilutata agg.). Again tips are given in the various books, but the wing markings are totally unreliable; and finally the Daggers. It has long been accepted that it is impossible to tell the Grey Dagger (Acronicta psi) and Dark Dagger (Acronicta tridens) apart, however it is possible to separate the males by examination of the genitalia, without killing them (see below).

I list below the results of dissections from moths collected in 2005, as a guide to how common various species were during that year.

Red Twin-spot Carpet and Dark-barred Twin-spot Carpet.

Both sexes were used as they are both very easy to separate by dissection of the genitalia.

Three moths were so badly worn it was not possible to see if they had a notch or not, so they have not been included in the above. All of the 'red' moths turned out to be Red Twin-spot Carpets in 2005, but this is not always so.

Common Rustic and Lesser Common Rustic

(Remm's Rustic has not been recorded here yet). Only males, which are easy to separate by dissection, were used for the survey. It is possible to separate the females, but it is also very easy to confuse them.

Common Rustic: 78, Lesser Common Rustic: 4

There was only one confirmed record of a Lesser Common Rustic on the county database before these were found. Many Common Rustics have been dissected in recent years, so it is possible that the Lesser Common Rustic is becoming commoner locally. All those that turned out to be Lesser Common Rustics were similar in appearance. They were all dark and similar in appearance to figure 5 on plate 38 of Skinner, but about 75% of the moths collected that looked like this were Common Rustics, so this colouration can only be used as a guide for what might be a Lesser Common Rustic.

Uncertain and Rustic

Only males were used, females being very difficult to separate.

Uncertain: 130, Rustic: 30

Marbled Minor, Tawny Marbled Minor and Rufous Minor

Males and females used in the survey, but approximately 90% of those collected were males.

Marbled Minor: 2, Tawny Marbled Minor: 134, Rufous Minor: 1

The drop in Marbled Minor numbers is rather worrying. In 2004 approximately 34% of those dissected were Marbled Minor. In previous years they have been commoner, but rarely as common as the Tawny Marbled Minor.

November Moth, Pale November Moth and Autumnal Moth

Males very easy to separate by dissection of the genitalia. Females very difficult. Only males used in the survey. 100% males collected.

November Moth: 8, Pale November Moth: 1, Autumnal Moth: 0

Very few were collected and sent to me this year. Last year all those dissected were November Moths, so it is pleasing to see the single Pale November Moth.

Grey Dagger and Dark Dagger

Females very difficult to separate. Only males used. Sixteen were sent to me. The others were identified by me while still alive.

Grey Dagger: 28, Dark Dagger: 4

To determine the two Daggers it is possible with the males to open the clasping organs and see the shape of the structure on each side with the use of a low power lens. Skinner and Waring et al. have illustrations of the structures. Place the moth head down, resting the head on your middle finger. Hold the body of the moth between the thumb and index finger, securely, but not hard enough to crush the moth. Now open the claspers with a needle or blunt tweezers and look inside. I find the moths more cooperative if they have been placed in ethyl acetate vapour for a minute or two, until they become calm. They recover from the fumes quite quickly and are soon capable of flying.

We can only guess at what the future will hold, now that DNA profiles are becoming easier to obtain. Several moth species have been already been looked at, and as more are done it is possible new species will be found and some will change families, but what that will mean for us in the field is difficult to speculate.

I would like to record my thanks to all the recorders throughout the county who collected moths for me to dissect. This is enabling me to get a true picture of the distribution of these difficult species.

References

Skinner, B. 1984. Colour Identification Guide to Moths of the British Isles. Viking. Harmondsworth.
Waring, P., Townsend, M. & Lewington, R. 2003. Field Guide to the Moths of Great Britain and Ireland. British Wildlife Publishing.