Tuesday, September 4, 2012

A Tar Sands Beetle, eh?

A male White-spotted Sawyer (Monochamus scutellatus)
A male White-spotted Sawyer beetle
Our local papers report almost daily on the numbers of young males flocking to eastern Montana's oil fields - and the problems associated with that demographic. But they never mention the White-spotted Sawyers (Monochamus scutellatus).

Just across the border in Alberta, they call this common long-horned beetle the "Tar Sands Beetle" because it flocks to places where natural tar (bitumen) is exposed. Near Fort McMurray, the Athabasca River cuts a channel through a bitumen-rich layer, and sunny summer days bring swarms of native Sawyers.

Why are beetles attracted to tar? Why alcohol, of course.

When exposed to sunlight, the natural bitumen emits terpineol vapors. Terpineol is a naturally-occurring alcohol that, it just so happens, is also found in pine oil. Pine oil is something we've used for years in deodorizers, disinfectants and antiseptics.

But terpineol vapors are also emitted by conifer trees in distress - burned, wind thrown, and fresh-cut live trees. And the White-spotted Sawyers seek out distressed trees as a good place to lay their eggs. After hatching, the grub-like larvae spend two years chewing their way around inside the log. This chewing can be disconcertingly audible to new log home owners, and it can decrease the wood volume by up to five percent.

The beetle itself seldom kills a tree, but problems associated with the young's lifestyle can. The grub's gallery and hole provides fungi with a point of attack. After a fire, this is a good thing because the fungi hasten wood rot and decomposition. But it's not so good for, say, a logging company because fungal "damaged" wood looses value and makes it harder to keep a ledger in the black.

Male Sawyers, like the one above, are all black except for a small white triangle (the "scutellum") at the base of their wing covers (click photo to enlarge). Male antennae are twice as long as their body, and twice a long as a female's antennae. Females might also be shiny black, but sometimes they have extra white spots on their wing covers. Adult Sawyers emerge between July and September to mate and lay their eggs on trees that smell good - to a Tar Sands beetle.