Have you ever been out enjoying a late spring or early summer walk only to be faced by entire plants, shrubs or even trees covered in what seems like a giant skin-tight spider web?
Don’t Panic
It may look like a scene from Lord of the Rings, but it’s actually the work of a small and mostly harmless moth.
On closer inspection of the web, you may well be able to see caterpillars roaming around underneath the silk. These are the larvae of the ermine moth.
The purpose of the web covering is not for catching prey like a spider’s web, it is to protect the caterpillars underneath from being eaten by any passing predators. Clearly the web is not impenetrable to larger predators, but it is a hindrance, and coupled with the large numbers of caterpillars present it gives the species a good chance of reproducing successfully.
According to the Butterfly Conservation Trust there are three species (in the UK) that exhibit such extensive vegetation coverage, they are the bird cherry ermine, the spindle ermine and the orchard ermine; telling them apart is tricky.
Sometimes these webs can cover entire trees, giving a quite shocking apocalyptic feel to your otherwise peaceful country walk.
But They’ve Killed the Tree!
The host plants may look dead due to the extensive defoliation caused by the legion of hungry caterpillars, but in fact the hosts are not usually killed. The defoliation may stress or even kill weaker or diseased hosts, but healthy plants will recover.
Once the caterpillars pupate, they will have stopped eating, giving the host the rest of the summer to grow back and thrive.
The Ermine Moth Life-Cycle
As mentioned above, ermine moths pupate in early summer and once they emerge, the adult moths will be active at night throughout July and August.
Their name comes from the fact that their colouration is reminiscent of the winter fur of ermines (stoats), that are white during the colder months.
During the summer, the adults will feed on nectar whilst searching for a mate. If they avoid predation and meet their mate, the female will lay her eggs, which hatch quickly into small larvae. These larvae will then over winter before emerging in spring to spin their giant, majestic webs and start the process over again.
All Part of Nature
These moths may cause unsightly defoliation of shrubs and trees, but they do not kill their hosts, and they are a member of one of our most critical and declining forms of life.
A recent Buglife study found that in the UK, flying insects have declined by 60% in 20 years, which if ignored (as it largely currently is) will have devastating repercussions for the future of life on this planet.
So, when you see a “ghost tree” full of caterpillars, thank your lucky stars because one day they may be gone forever.
