On Unintended Consequences, or, Bacillus thuringiensis

Once upon a time our shack in Severn County backed onto a forest with lots of wildlife. There were garter and water snakes on the rocks out by the dock, frogs, grasshoppers, crickets. We had bats in our bat-house, orioles on a beaver pond point, the odd wren and brown creeper, red-eyed vireos nesting, and the occasional robin. We used to hear whip-poor-wills and woodcocks. (We also had the odd rattlesnake, so caution especially for small people, was always requested.)

Then we had the gypsy moth. Its caterpillar is hard on trees, especially oaks. The smaller one on our tiny property was reduced to a stub, but the shoots grew back later into a sort of briar-patch of saplings.

So, a company (Zimmer Air, as I recall) offered us gypsy moth spraying. Now this is from memory, but the contract was written so that a sudden wind could blow a hole in it. If we agreed to pay, we paid even if the spraying missed the target.

What I remember most about the glossy brochure they left in the shack door was, what they said about Bacillus thuringiensis. (The bacterium creates insecticidal crystals that kill insects.) Quote: the gut of an insect is alkaline, and human stomaches are acid, so the bacterium cannot flourish there. Fact: the human intestine is basic. There is actually some doubt as to the non-toxicity of this bacterium, commonly referred to as B-t.

I refused to pay for the spraying, and hoped my neighbour would too. She did, but she explained she (as neighbour) was allowing the next property over to be sprayed. They have a lot of large oak trees, so I gave no objections. Spraying occurred.

Now for the result:

  • No insects with non-aquatic larvae. No grasshoppers. No crickets.
  • No frogs, no snakes, no toads, no bullfrog calls.
  • No orioles, no bats, no thrushes, no whip-poor-will calls.

Deer flies, horse flies, black flies: yes. Few dragonflies. Fewer mosquitoes.

Chipmunks, flying squirrels, squirrels, yes. Terns, gulls, herons, less. No cormorants. No buffleheads.

A decade later there is a faint sign of recovery. We saw one small toad this year, and I think a mink frog. No swallows yet, and only one tern.


Broad-spectrum spraying can have unintended consequences. Like giving a small child antibiotic, to discover this increases the chances of asthma later in life.

It is not clear overall that the unsprayed forest is worse off. A few oaks in the deep bush succumbed, but some did not and some recovered. There was worse forest damage by a wind storm, which took down most of the pines in what must have been local wind concentrations.

Still, there is no oriole nest on the beaver pond rock we still call Oriole Point. The number of chickadees coming to the feeder used to be eight; this year it’s three or four. (I think most bird nestlings are insectivorous and learn to eat seeds later, like weaned children.)

Since I almost always include a dumb question, here is today’s:

Is it smart to interfere with an ecosystem, risking unintended consequences?

Leave a Reply

Your email address will not be published. Required fields are marked *