Species of the Month - March 2019
The Red Sword-grass is a large and distinctive moth that often comes to lit windows (or moth traps) in March and April, and is also frequent in October and November, hibernating as an adult moth during the cold of winter. It mates in the spring, and the caterpillars are active, but nocturnal, from May to July, feeding on a variety of plants including heather, bog myrtle, sedges and rushes. They inhabit damp ground in either wooded or open country.
can appear as early as the end of August and as late as the following
early June, and is thus one of our longest lived moths". (Clancy 2012).
Our earliest is 27 September and our latest is 7 May, so perhaps it
doesn't live quite so long in our climate as further south.
Sword-grass rests with the wings wrapped around the body. In this
position, the inner part of each wing (on top of the moth) is a deep red
brown, and the outer/lower part is a pale straw colour. This
contrast extends for the whole length of the moth, and distinguishes it
from the Sword-grass, the only possible confusion species, which could
conceivably occur here though we have no records of it. In the Sword-grass,
there is little contrast between the outer and inner parts of the wing,
except near the head.
red-brown tones seen here in the Red Sword-grass are absent in the
Sword-grass which is a much greyer moth.
The wings are 24-29 mm long, making it one of the largest moths you are likely to see in early spring.
colouring of the face and the long narrow rounded body mimic a broken
twig, making it hard for predators to spot when resting on a tree or
We have two records of the caterpillar. This one was on heather on Rannoch Moor and was about 49 mm long, on a date of 9 July. The size of a fully-grown caterpillar is 52-60 mm, and it can be pale green, dark green or black; this one was the pale form. (see ukleps.org)
Our other larval record was on 1 July and not seen by me, but it was reared by Clive Craik and the adult emerged on approx. 19 September.
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