Is Stirling ready for Halloween already?

No; as Athayde Tonhasca explains, these eerie-looking bushes in the Wickes car park are covered by webs produced by hundreds or perhaps thousands of caterpillars of small ermine moths.

The ermine moth's web at Wickes car park in Stirling. ©Stephen Longster

The ermine moth’s web at Wickes car park in Stirling. ©Stephen Longster

We tend to associate silk webs with spiders, but in fact many plant mites and insect species are also capable of spinning webs. And among them, some species of small ermine moths (genus Yponomeuta), so called because the adult coloration resembles the heraldry’s ermine pattern of a white background dotted with black shapes, are truly spectacular spinners, capable of producing copious amounts of webbing. For reasons not completely understood, occasionally these micro-moths go crazy with their webbing, enveloping with silk not only their host plants but also nearby objects such as fences, benches, bicycles and even cars.

One of the many varieties of ermine moth. Creative Commons image.

One of the many species of ermine moth.  Creative Commons image. CC licence..

The main reason for the webbing is protection; the larvae emerge in spring and set off feeding gregariously on the newly emerged leaves of the host plant. Without the webs, the small caterpillars would be easy prey for predators and parasites. The silk layers may also help in thermoregulation, maintaining a nice and cozy environment inside the moths’ ‘tent’.

From time to time ermine moth populations increase so much that entire trees and hedge lengths are completely defoliated, leaving their skeletal remnants covered with a coating of silky webbing. These ghostly visions may be alarming, but control measures are rarely necessary; the moth populations soon crash, the webs slowly disappear over the summer and the host plant produces a fresh flush of leaves, recovering quickly from the damage.

For more information about ermine moths, see Butterfly Conservation’s Don’t worry about ermine webs .

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