Wind Turbines and Insects

That wind turbines kill insects doesn’t bother most people, but as with the “butterfly effect”, the consequences may be understated.

The wind industry has had green tailwinds for a couple decades. In 2015 the wind industry was granted license to kill up to 4,200 bald eagles a year in the U.S., for 30 years. The Bald and Golden Eagle Protection Act prohibits killing of these birds at all, a measure of the power of the ‘renewables’ trend.

But this isn’t about the birds. Or bats. They appear higher up the food chain and their destruction is already well known. This is about the lowly insects.

Interestingly the wind industry studied insect kills not because they like insects (though a 75% reduction in insect biomass contributed to the Trieb study cited below), but rather because dead insects collecting on blades decrease efficiency by up to 50%, a drag not accounted for in engineering projections for turbine power generation. Dead bugs on rotors is an economic problem. But it’s also an environmental problem.

Wind farm insect destruction estimates continue to rise with new studies – measuring, and adjusting models based on previous work – so it make sense to examine from the beginning, adding the factors that have brought us to today’s understanding. Expect more of this as pressure increases to quantify costs more accurately.

For insects, a trifecta of factors come together for results far beyond initial assumptions: concentration, life cycles, and predation.

Insect concentration in the air was initially a simple extrapolation of the windshield effect: drive along any highway in the north country in Spring, and notice the number of mosquitoes and black flies on your windshield along the way. With a high concentration of bugs at that time of year, your windshield will take out those pests who by sheer stroke of bad luck happen to be on that stretch of road when you come along. Traveling the Trans-Canada in May or June with hundreds of miles to the next highway and a lot of woods and water in between, you don’t much worry about the insects with the bad luck to meet your windshield. But we don’t need to. It’s de minimus, concentration is limited by the season, and random (for the bug).

But insects also migrate, leaving the realm of random and entering into increasing levels of concentration. Several factors are at play, beginning with altitude. Economy of effort – characteristic of all life forms – takes migrating bugs above the “surface layer”, roughly 15 – 25 meters high with less turbulence above that level, into favorable currents, up to around 250 meters. This behavior results in higher concentration by orders of magnitude on favorable prevailing winds. It’s why pilots hitch rides on jet stream currents to get you across the country ahead of schedule. But wind farms choose these altitudes and favorable prevailing winds as well. Wind farm siting is not random like your car on a bug infested highway; it’s at the heart of many migratory paths, from 25 meters to 250 meter high.. Path concentration and altitude concentration are not coincidental; it’s where the wind is best, for migration, and for wind farms. It’s where they both concentrate.

Insects move most when seeking food, better weather, or for breeding; this is the life cycle effect. We learned about insect life cycles in grade school: eggs, larva, pupa, maturity: the last stage is when they get wings and breed. They don’t move much in the first stages, but go furthest when getting ready to breed. The mass killing of insects – over a trillion a year estimated in both England and Germany – is further compounded, exponentially – where real change occurs – by the effect of lost eggs and lost future offspring over time.

Predation is another natural force unaccounted for. Thanks to coyotes and other scavengers, evidence of dead birds and bats is conveniently erased from many neighborhoods around turbines. But compounding predation happens before most insects even reach the ground.

Nature doesn’t waste much; dead or wounded animals soon become food for others. Insects aren’t only killed when they slam into the leading edge of a turbine blade.

Air pressure is the power behind converting wind into electricity, and powerful too near a turbine blade. Just as the difference in air pressure on the wing of a plane creates lift, the same air pressure differential rotates blades in the wind. Barotrauma is the term for what happens to insects (and birds and bats, by the way) when the air pressure changes by up to 100 hPa on the back – suction – side of the blade. This is roughly equivalent to going from sea level to 1,000m or 3,000’, in an instant. This shock kills some, but disorients many others; both attract opportunistic predators. The wind turbine becomes a huge odor attraction point, its own black hole of a food chain, with a predictable end. Just ask bats or larger insects what it’s like to feast on disoriented bugs, when… Whack!

This trifecta of forces clearly affect insect populations. Most of what I’ve summarized here was inspired by Franz Trieb’s 2017 report,. That report was in turn partially inspired by the loss of insect biomass of 75% in the decades since wind farms came to Germany. It’s not just the estimated 5% of insects that don’t survive transit through turbines, but the cumulative effect over time. The power of these trends is the compounding.

Just as the 2015 Obama administration ruling that permitted the killing of up to 4,200 bald eagles every year for 30 years was deemed the acceptable price of wind energy, new studies outlining previously ignored external costs are now being added to the equation when calculating ‘sustainable’ power. All should be added to the mix to understand the forces and costs.