Web spinners envelop Kitimat trees

You could be forgiven if you thought a Hollywood movie crew were in town filming a low budget Hallowe’en movie.

Dennis Horwood

You could be forgiven if you thought a Hollywood movie crew were in town filming a low budget Hallowe’en movie.

Several trees adjacent to Centennial Park were recently shrouded in sticky silk, reminiscent of just about every scary movie California film companies have ever made.

Just standing beneath the veiled branches was enough to set your spine a-tingling.  You might almost have been breathless in anticipation of some zombie-like creatures emerging from the thousands of cocoons hanging in clumps midst the bark and branches.

As weird a scene as the trees presented, no movie was made nor did anything untoward emerge unless you have a distinct dislike of very small bugs.

There is, however, a story to all this which began some 30 years ago.

In 1981, staff at a nursery in Duncan first noticed an insect on their trees previously unknown to them.

In the next decade, the same insect appeared throughout southern Vancouver Island, Greater Vancouver, Fraser Valley and in 1988 as far north as Pemberton.

By the next year, the Pacific Forestry Centre was following the spread of this new bug, now appearing throughout the Sechelt Peninsula and north to Boston Bar.

They were not at all pleased, however, to identify this new tree pest as the apple ermine moth, an unwelcome immigrant from Europe.

Ermine moths are rather small, being only about 1 cm long. Their larvae are about the same length and dark overall making them blend in quite well against a tree branch.

As the larvae begin to gorge on the fresh leaves, they spin webs covering the leaves and branches. In the right conditions, the webs eventually cover every leaf and branch right down to the base of the trunk and spreading out onto the ground.

The thin web is easily broken but serves as a protective shield from predacious birds and wasps.

In a week or two, larvae can completely defoliate a tree. Once the larvae have had their fill, they collectively spin white, spindle-shaped cocoons loosely packed together for another two weeks.

These collections of cocoons have a loose similarity to  Species, a sci-fi Hollywood thriller. The cocoons hanging in the apple trees will not, however, produce aliens with powerful DNA.

Rather, a small, white moth will emerge. The females will feed on flowers for a short time and then begin their egg-laying cycle.

The eggs will be deposited on the bark and covered with a hard secretion. They are difficult to detect and well protected from the weather and hungry birds.

Before the summer ends, the eggs hatch but the tiny larvae remain immobile beneath the covering until next spring.

The ermine moths that have defoliated the trees in the city centre park will likely persist into next year.

Enough adults have already emerged and scattered to be reasonably certain they have spread to other neighbourhoods.

They seem particularly partial to apple and crab apple trees. Unfortunately, many other fruit trees belong the same biological family which includes cherries, peaches, and even raspberries or strawberries.

Anyone with gardens or fruit trees would be advised to alertly watch for any signs of an infestation next spring.

If discovered, the infected branches should be removed and destroyed.

The alternative is to leave them unmolested whereupon they may create a pseudo-Hollywood movie set in your backyard.