73.361 Xestia triangulum (Double Square-spot)
fw: 17-19mm; Jun-Aug; various herbaceous and woody plants; common throughout GB.
ID: This species and X.ditrapezium (Tripple-spotted Clay) have the same basic pattern of markings: an indistinct pale basal line bordered proximally by two black dashes; a pale straight antemedian line bordered proximally by a narrow black line; a pale curved postmedian line; an indistinct pale subterminal line with a short bold black bar bordering its costal end proximally; a pale outlined narrow kidney mark; a broad black streak in the centre of the wing between the antemedian line and the proximal border of the kidney mark and almost completely interrupted by the oval mark so that it appears as two black squares. There does not seem to be any logic to either the English or scientific names of these two species and any attempt to identify them on the assumption that there is any logic to them will result in confusion and error. They may be separated on the following external features: 1. X.ditrapezium has a narrower forewing (with practice this is quite a useful feature); 2. Forewing ground colour in X.ditrapezium ranges from reddish-brown to purplish-black, X.triangulum is usually light greyish brown (but may have reddish tones and/or be darker); 3. Hindwing is brown with orange-brown cilia in X.ditrapezium and grey with whitish or grey cilia in X.triangulum.
All images © Chris Lewis