Species Account

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Distribution


 
 

Summary Data


Season (Adult / Immature):

National Status: Common

Local Status: Scarce and thinly distributed resident.

Local Record: Grade 3   See here for explanation

Flight time: Two generations, Apr-Jun, Jul-Aug.

Forewing: 12-13mm.

Foodplant: Herbaceous plants.

IMPORTANT - Please note that the maps and accounts are provisional, subject to change and further update.  The whole dataset still needs to go through the final verification process and it is likely that a very small number of records will not satisfy the present requirements and there are other records that have not been formally submitted.  The information is for guidance only.

Record breakdown:

 VC9VC11Region
Year first recorded192919701929
Year last recorded201120112011
Number of records4381101096
Number of individuals6641331594
Unique positions488112
Unique locations458106
Adult records4291081074
Immature records000

For the region, we have a total of 1096 records from 106 sites. Earliest record on file is in 1929.
 

Photos


1725 Dark-barred Twin-spot Carpet 02
© Dave Foot
1725 Dark-barred Twin-spot Carpet 01
© Tom Morris

Species Account


Similar species: 1724 Xanthorhoe spadicearia (Red Twin-spot Carpet).

For further information refer UK Moths.

Davey, P., 2009: A widespread species in Britain, the larval foodplant is unknown. In Dorset, the moth is very local, being recorded from marshes, river banks, wet margins and ditch habitat where common marsh-bedstraw (Galium palustre), fen bedstraw (Galium uliginosum) or water dock (Rumex hydrolapathum) are potential foodplants. This species is likely to have a similar distribution to that of the Oblique Carpet1719.

The moth is rather difficult to separate from the Red Twin-spot Carpet1724 at first glance. Diagnostics include: a lack of pinkish ground colour; a greater contrast in forewing colours; a single deep notch on the outer edge of the median band; restricted to damp habitat. The flight periods of the two species coincide.

Hill, L., 2013:

Forewing upperside: Broader median band irrespective of colour which can be 'red' to 'dark'; more obvious ‘step’ where central band broadens; no distinct postmedian white line along edge of median band, however, some specimens may have what appears to be an indistinct whitish postmedian line. The apical area near the ‘twin-spots’ is less-richer in colour than in Red Twin-spot Carpet and the ‘twin-spots’ are usually more isolated from each other.

Underside: uniform grey; little contrast. Red Twin-spot Carpet has strongly contrasting pattern; deep ‘ginger’ colouration towards the apex of the forewing.

Some of the upperside diagnostics are subjective so whenever possible, refer to the underside.

Differences in wing markings between Xanthorhoe ferrugata (Cl.) and X. spadicearia [(D. & S.)] (Geometridae) are discussed. Examination of a long series of male genitalia confirm that presence of a notch in the inner edge of the central forewing fascia near the costa, is an unreliable determining feature. Approximately one third of X. spadicearia and two-thirds of X. ferrugata are notched. The degree of contrast between the pale post-median fascia and the terminal and sub-terminal areas, and other features of banding are useful indicators, and can in combination be used to safely identify many specimens. The red-banded and dark-banded forms in X. spadicearia form a continuum and are not clearly distinct as in the black-banded and red-banded forms of X. ferrugata. Examples with bold underside markings are likely to be X. spadicearia. Recording bias created by use of the notch is likely to favour X. ferrugata and would therefore have partly masked any decline in X. ferrugata. The 92% decline in X. ferrugata, as recorded in long term light trap data, is unlikely to have been affected by any bias. The apparent scarcity of the typical form of X. ferrugata (with red median forewing fascia) would appear to be genuine (Townsend, 2010).
In accordance with (Townsend, 2010), all records of X. ferrugata Dark-barred Twin-spot Carpet must be considered unsafe if determined by the notch character alone. This is likely to be the majority of Dorset records.

Reference
Townsend, M. 2010. Observations on the use of wing-markings and genitalia to distinguish Dark-barred
    Twin-spot Carpet Xanthorhoe ferrugata (Cl.) and Red Twin-spot Carpet X. spadicearia ([D. & S.])
    (Lep.: Geometridae) and on the implications for recording these species. Entomologist's Rec. J. Var.
    122(3):120-127.

Last updated: 22 August 2013

 

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