Euxoa
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311 Euxoa cursoria (Coast Dart)
fw: 14-18mm; Jul-Aug; various sand-dune plants; NS-B on coastal sand-dunes of northern England and Scotland from Lancashire to Norfolk. |
312 Euxoa obelisca (Square-spot Dart)
fw: 14-18mm; Aug-Oct; common rock-rose (Helianthemum nummularium), lady's bedstraw (Galium verum); NS-B on rocky and hilly coasts in S&W England, Wales, Scotland and Northumberland. |
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313 Euxoa tritici (White-line Dart)
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314 Euxoa nigricans (Garden Dart)
fw: 15-18mm; Jun-Aug; various herbaceous plants; said to be common throughout GB |
Euxoa - external features
The four British Euxoa species can be very similar and E.tritici is so variable that it can resemble any of the other three. E.obelisca is confined to sea-cliffs and rocky coastal hillsides. E.cursoria is confined to coastal sand-dunes. E.tritici and E.nigricans are widespread. Specimens showing a series of black interneural streaks or arrowheads projecting proximally from the subterminal line will be E.tritici. All except E.nigricans may show a pale subcostal streak. In E.obelisca the postmedian line runs close to the distal border of the kidney mark and the terminal area of forewing, distal to this line, is fairly uniform grey-brown to reddish. In the other three species the postmedian line arcs fairly widely around the kidney mark and in E.tritici and E.cursoria the terminal area of the forewing is more variegated. In E.obelisca the antemedian line approaches the dorsum at 90° and usually extends through the pale costal streak; in E.tritici the antemedian line approaches the dorsum at an acute angle and disappears at the pale costal streak (when this is present). On the forewing underside E.cursoria has a large blurred kidney mark with a pale band distal to it; E.tritici has a small crescent mark and no pale band. On the hindwing underside E.tritici has a terminal band of dark shading which is not seen in E.cursoria. (Waring and Townsend is confusing about these underside features - which are illustrated and better described in MBGBI9 p133).
The four British Euxoa species can be very similar and E.tritici is so variable that it can resemble any of the other three. E.obelisca is confined to sea-cliffs and rocky coastal hillsides. E.cursoria is confined to coastal sand-dunes. E.tritici and E.nigricans are widespread. Specimens showing a series of black interneural streaks or arrowheads projecting proximally from the subterminal line will be E.tritici. All except E.nigricans may show a pale subcostal streak. In E.obelisca the postmedian line runs close to the distal border of the kidney mark and the terminal area of forewing, distal to this line, is fairly uniform grey-brown to reddish. In the other three species the postmedian line arcs fairly widely around the kidney mark and in E.tritici and E.cursoria the terminal area of the forewing is more variegated. In E.obelisca the antemedian line approaches the dorsum at 90° and usually extends through the pale costal streak; in E.tritici the antemedian line approaches the dorsum at an acute angle and disappears at the pale costal streak (when this is present). On the forewing underside E.cursoria has a large blurred kidney mark with a pale band distal to it; E.tritici has a small crescent mark and no pale band. On the hindwing underside E.tritici has a terminal band of dark shading which is not seen in E.cursoria. (Waring and Townsend is confusing about these underside features - which are illustrated and better described in MBGBI9 p133).
Male genitalia - illustrated in MBGBI9 p131,135; described and illustrated in the Difficult Species Guide
In E.cursoria the ventral saccular processes are asymmetrical, longer on the right; they are symmetrical in the other three species
In E.tritici the notch in the apex of the juxta extends less than 1/3 of the length of the juxta*; more than 1/3 in E.nigricans and E.obelisca
In E.nigricans there is a distinct bulge at the ventral angle of the cucullus which is is lacking or only slight in E.obelisca
* In specimens I have examined that seem to be E.tritici the notch in the juxta is slightly more than 1/3 the length of the juxta - so I am not at certain that the figure of 1/3 is sufficiently accurate
In E.cursoria the ventral saccular processes are asymmetrical, longer on the right; they are symmetrical in the other three species
In E.tritici the notch in the apex of the juxta extends less than 1/3 of the length of the juxta*; more than 1/3 in E.nigricans and E.obelisca
In E.nigricans there is a distinct bulge at the ventral angle of the cucullus which is is lacking or only slight in E.obelisca
* In specimens I have examined that seem to be E.tritici the notch in the juxta is slightly more than 1/3 the length of the juxta - so I am not at certain that the figure of 1/3 is sufficiently accurate
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Female genitalia - illustrated in MBGBI9 p131,135; described and illustrated in the Difficult Species Guide
Distinguished by the length of the basal spines on the anal papillae - short in E.cursoria, intermediate in E.tritici and long in E.obelisca and E.nigricans. The latter two may be distinguishable by the shape of the bursa copulatrix which has an almost straight left margin and pointed anterior and posterior apices in E.nigricans; broad and rounded in E.obelisca.
Distinguished by the length of the basal spines on the anal papillae - short in E.cursoria, intermediate in E.tritici and long in E.obelisca and E.nigricans. The latter two may be distinguishable by the shape of the bursa copulatrix which has an almost straight left margin and pointed anterior and posterior apices in E.nigricans; broad and rounded in E.obelisca.
