Thanks to the sharp eyes of Iain Leach we have another micro moth to add to the Scottish list! This tiny moth, the Large Orache Case-bearer, is just over 8mm long, and is a member of the family Coleophoridae. All 104 species of this group that are found in Britain, are small (wings 3 to 11 mm long) and look quite similar i.e. slim, elongated, hold their body higher at the front when at rest (see photo below) and keep their antennae stretched out forward. The hind wings have a very long fringe of hairs along their trailing edge. Generally the adults are pale coloured, often with speckles of darker scales or with obscure longitudinal streaks. However, although many of the adults are difficult to identify, their larvae can often be named from the size, shape and colour of the ‘case’ in which they live, along with the food-plant on which they feed. These cases are made from parts of the foodplant and shelter the growing caterpillar. Most species hibernate at the base of the plant.
This particular species was first found in Britain in 1958 and is on the wing from the very end of June through to August and comes to light. This one, the first record for Scotland, was found on the 5th July on SWT’s Southwick Coast Wildlife Reserve. Although it stood out as something different, it was not possible to identify it without looking microscopically at its genitalia. This is not only a very difficult and delicate task but, in many cases, it can be difficult to work out which species you have from the results! However, in this species the male genitalia are very distinct and the identification was straight forward.
What was surprising was that the nearest known population of this case-bearer is in coastal Lancashire, although it is mainly found in south-east England and along the south coast. There are relatively few records of this moth anywhere and it is regarded as Nationally Scarce (i.e. only occurring in 16 to 100 10×10 kilometre squares in Great Britain).
Because the next nearest population is so far away it is unlikely that this moth has accidentally strayed as far north as us. It is more feasible that it has been in D&G all along and our next step must be to see if we can find the evidence for it breeding here. The easiest method would be to search the foodplants for the tiny larval case. The foodplants include a number of the oraches, most of which grow on the seashore or in salt marshes although some species do live inland on disturbed soils. Most records seem to be from Grass-leaved Orache or from Sea Purslane, both of which grow along the Kirkcudbrightshire coast. The moth lays its eggs in the flowers and the young caterpillar begins to eat the seeds as they develop. The growing larva starts to form a case from pieces of leaf and feeds on the leaves from the mouth of the case. The mature caterpillar can be found in a pale, ribbed case with brown stripes about 8mm long (see photo below) which normally sticks out vertically from the leaf at about 10 degrees. The fully grown caterpillar descends, inside its case, to spend the winter in the leaf litter at the base of its foodplant.
With such tiny insects restricted to specific plants it will require good eyesight and a lot of patience to find these larvae. However, crawling around the sea shore, on your hands and knees, could be a pleasurable activity in the sunny (hopefully) days of August and September. Good luck to anyone who gives it a go! Do let me know if you find anything.
