Moth Trapping 1/2 August

The evening of Friday 1st August was perfect for moth trapping, with no wind, warm temperatures, high humidity, and thin cloud. George Guthrie, a colleague from insect monitoring at the Loch Leven NNR, had offered to bring his moth trap, and his extensive experience, to give us a chance to see what moths may be found in our woods. As my garden adjoins the edge of Hopeward Wood this seemed a suitable location for this first “look see”, and we set the trap up on the lawn beside the wood. Then, as darkness started to fall after 9 pm, it was switched on. The trap uses a powerful light with a high UV component which attracts the moths. Some enter the opening around the light and remain within the trap until released.

To shelter them inside the trap there are irregularly placed black painted egg cartons and these give them a place to rest until they can be examined as can be seen in the adjoining photo of the Scalloped Oak.

The trap was placed on a large white sheet on which more moths alighted and these were put into small containers to await examination the following morning. There was soon a steady stream of moths coming in and Blair and I spent the next couple of hours transferring the ones on the sheet to their temporary accommodation. The trap was switched off at around 4 30 am and any moths remaining on the sheet were gathered up and a cover was put on the trap. This is an important step in the process as otherwise keen eyed birds like robins and sparrows would simply find a feast laid out for them as the moths continued to rest on the sheet, while the birds started to become active with the growing light of morning.

George and Blair returned at around 7 30 am and George began the process of identifying and counting the moths while Blair and I supervised their return to dark corners of the adjacent hedge where they would remain until the evening when they would fly off once again.

This also provided an opportunity, before the rain came, to get a few photographs of insects that are an important part of our woodland ecology but are rarely seen. All the moths that came to the trap were species that spend the daytime resting, and their colouring has evolved to make them inconspicuous and difficult to find for the various woodland birds that would make a meal of them. So colours are generally soft browns and greys, reflecting the kind of surfaces and locations where they rest.

By far the most abundant were two kinds of Yellow Underwing moths. These may be familiar to any gardener who does any rootling around in overgrown areas of the garden at this time of year. When disturbed they fly erratically, displaying a flash of yellow, and then disappear again. This is also part of their anti predator strategy. The bright yellow of the lower wing attracts the eye, but when it vanishes, the bearer of the bright colour appears to vanish as the dull and cryptically coloured upper wings once more cover over the bright lower wings. As all the moths photographed were in the resting pose, the pictures below show only the camouflage patterns of the upper wings.

These two species feed as caterpillars on a range of herbaceous plants and grasses and they rest up in the dead leaf layer at the bases of hedges and under dead vegetation, and this is reflected in their upper wing colours. Most moths when examined from the trap betray their preferred resting places in their wing colours. The pale Smoky Wainscot will be found among the pale stems of the grasses on which its caterpillars feed, and the Willow Beauty looks as though it would hide, but in full view, on subtly patterned tree bark, and this species feeds on Hawthorn and other deciduous trees. Resting on a window frame however is not where it will easily blend in and this one was moved to a more appropriate resting place for the remainder of the day.

Many species have lines that draw the eye to an irregular pattern of lines and shapes which, like the dazzle pattern of wartime ships, serves to disguise the true shape of the moth when resting among dead leaves and other vegetation. Some species show the same basic pattern, but with slight colour and pattern variations as in the two Dun-bar moths shown below.

Altogether George used his expertise to identify some 32 species in the 384 moths that were captured that night. The full list is shown below along with some indication of the food plants of the caterpillars. As you can see there is quite a variety of plants that are used for food ranging from trees such as Ash and Sycamore to the lichens and mosses that grow on tree trunks. Not all feed on leaves, some eat grass roots and others flowers or seeds. The caterpillar of the Rivulet eat the seeds of Red Campion, a flower that is common on the path margins of our woods, and will move from seed capsule to seed capsule devouring the seeds contained within the open seed cup.

This list is only an indication of what can be found at this time of year and in this part of one wood, if trapping was done at a different time and a different woodland location there would be many other species not included in the list below. Altogether, in both species and individual numbers, moths far exceed their more conspicuous daytime family members, the more familiar butterflies. For those who are interested, photographs and information on some 2226 of the 2400 British moths can be found at http://ukmoths.org.uk which gives a fascinating collection of images and knowledge.

George has offered to come again with his trap and wide knowledge of moths and set it up in another location so we can get a further view of what we are conserving in our woodlands, and providing an interesting experience for any who want to come along, old or young.