Gardening: Time for autumn spiders?

Buff Ermine and White Ermine Moths by Paul Ardron
Buff Ermine and White Ermine Moths by Paul Ardron

This time of year frequently brings a flood of enquiries about spiders and especially spiders’ webs appearing everywhere. By late summer and early autumn, weather depending, we begin to get large spiders in houses, outhouses and gardens.

However, we also see spiders’ webs, from small to potentially quite large. Some of these in hedgerows, increasingly in the coming weeks, are so-called ‘blanket webs’, essentially like sheets of textile hanging vertically from threads above and secured by threads below. The other main structures are ‘orb webs’; big roughly round webs secured by threads around them like the spokes of a wheel and behind too. Especially noticeable in the early autumn on a cold morning with heavy dew, these always get comments.

However, there is another source of readers’ concerns and this may blanket many square metres of vegetation, especially garden shrubberies. Remarkably, the sheeting of web is not caused by spiders, but by a moth, the buff ermine. The moth is so named because of the adult’s gorgeous markings like a stoat in winter ermine. Reader Charles Thompson was in touch because a bush outside the house of a friend’s mother was ‘seemingly overtaken by spiders’ webs, so dense that they have killed off the bush and is quite a sight to behold. The web is completely covering the 2.5ft high by 8ft bush.’ This is indeed the work of the buff ermine moth (spilosoma luteum), and is how the caterpillars protect themselves and their food from predators. The culprit breeds on various shrubs, so they do well on ornamental shrubberies.

The moths fly during August and lay eggs, from which hatch caterpillars that feed on the bush. The youngsters hatch quickly and the caterpillars eat a lot and grow fast. The young larvae of the buff ermine generally live close together in large groups, but split up once they are older. These gregarious caterpillars gorge on infested areas of shrubs such as dogwood, buckthorn, blackthorn and hawthorn, stripping whole bushes. They live beneath silk webbing to protect them from predators and parasites, and sometimes cover many square metres of foliage. The larvae, especially when older, are extremely mobile and can cover large distances quickly (at least for a caterpillar). When threatened they freeze or quickly run away. In autumn, the larvae weave greyish black cocoons within which they pupate among leaf litter and other plant debris during winter, to hatch the following year. Interestingly, the ‘epidemics’ are sporadic and seasonal one-offs as the caterpillars use up their food supply and have to move on as a ‘boom and bust’ species. This means there probably will not be any in that area the next year, so for gardeners, there is no point in spraying. The caterpillars are harmless to us.

- Sightings: Lowland wetland sites, lakes, flashes and reservoirs are good at this time of year. Catcliffe Flash for example, has had pintail, shoveler, wigeon, pochard (up to 44), 11 little grebes, great crested grebes (apparently being aggressive towards the little grebes), seven mute swans, eight teal, and a kingfisher. Other sites such as Orgeave Lakes and Elsecar Reservoir had juvenile Arctic terns, and the latter had nine great crested grebes and 11 coots. Quite a few birds such as wrens, dunnocks, robins and blackbirds are still singing in woods and hedgerows, particularly in late afternoon and early evening. Warblers are still with us but are mostly silent or just calling. Watch for the magnificent red deer stags on the moors west of Sheffield.

- Professor Ian D. Rotherham, researcher, writer and broadcaster on wildlife and environmental issues, is contactable on ianonthewildside@ukeconet.org ; follow ‘Ian’s Walk on the Wildside’, www.ukeconet.org for more info.