THEY are the ‘ghostly’ forests of cobwebbed trees whose spectre haunts woodlands throughout Europe.
Now the sinister sight of cherry trees draped in eerie cobwebs is taking hold in Scotland after the beast from the east Siberian storm and recent heatwave created perfect conditions for the phenomenom.
Huge numbers of bird cherry ermine moth caterpillars has created the spectre in woodlands across the country as they spin elaborate webs to protect them from predators.
They feed on bird cherry trees which are found across Europe and when they emerge fully grown, they become distinctive white moths with five rows of black dots.
The larvae, which are about an inch long, make large communal silvery webs for protection and then feast on the surrounding leaves, stripping the trees bare.
There are eight species of ermine moths in this country and 2,400 species of moths in the British Isles and they usually pupate into adult moths in July or August.
The Woodland Trust Scotland has been receiving many reports of the ghostly looking trees in recent days with worried callers expressing alarm at the trees being stripped of all vegetation.
But the trees are not killed and will recover next year, by which time the caterpillars will have found somewhere else to spin their webs.
The Trust has received calls about outbreaks at Formonthills in Glenrothes and at its own Geordie's Wood at Glen Devon with the species enjoying a bumper year across many parts of the country.
George Anderson of the Trust said: "Every few years this species explodes in numbers and they strip the host tree of its leaves. Trees normally recover the following year so it is not as drastic as it looks.
It does look very sinister as they drape entire trees in their silk. We have had some enquiries from people concerned that they were seeing oak processionary moth.
"These are a real problem in the south of England and cause severe allergic reactions but thankfully they have not been found in Scotland. It is the bird cherry ermine moth we are seeing at the moment and it is entirely harmless."
The bird cherry moth, Latin name Yponomeuta evonymella, has a maximum wingspan of less than an inch and is found all over Europe.
There are hundreds of known species of ermine moths, and most of the time they go completely unnoticed.
But when it comes to spinning elaborate webs, no creature can match the power of ermine moth caterpillars. The behaviour is called “tenting,” and only some species are able to manage it.
Every now and again, thousands of the tiny moths show up en masse and it is happening more frequently.
By working together, they are able to conceal themselves in a protective blanket. Like a giant invisibility cloak, the veil confuses birds and other predators well enough to keep them at bay while the caterpillars feed.
As the ermines move from tree to tree, they have to cover their tracks and so they keep their protection with them.
Over time everything in their path, from cars, to street signs, to grass, becomes shrouded in white, a scene which has been nicknamed the “walk of ghosts”.
One theory suggests that the super-webs form when multiple females lay their eggs on the same plant, in areas where food is scarce such as housing developments.
Other experts suggest that climate change is having an impact as the eggs tend to do better over warm and damp winters.
Experts believe that the sever storms which swept in from Siberia in March followed relatively shortly after by a prolonged heatwave has provided perfect conditions for the moths, while killing off their parasitic predators.
Tom Prescott, Senior Conservation Officer at Butterfly Conservation Scotland said: "They are targeted by parasitic wasps and flies who enter their bodies and hatch out when the moths should and kill them off.
"It's why they make this incredible web, they hope to keep the parasites and other predators out, it's like a very large disguise.
"It just takes two or three to get inside the blanket for the moth numbers to be dramatically reduced, this is why some years there are lots of them, while in other years you can hardly see them.
"We don't know for sure but the cold spell could have hit the parasites numbers while the recent warm spell has made it great for the caterpillars, one minute it was grey and overcast and the Spring and Summer both seemed to appear at once.
"We have another species in Scotland, the Marsh Fritillary, which spins similar webs to protect it from its only known parasite, but there are smaller numbers of them and its population fluctuates much more from year to year.
"But in truth, we don't really understand everything about the bird cherry ermine months and the webs but it can certainly put on a show".
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