As a squadron of dragonflies flies low over the bogs of the Kenai Peninsula, the drone of their wings strikes terror into the prey in their path. Mosquitoes, flies, even bees scatter. But this day they are not after bugs. This day they are after much bigger and much easier prey.
The head of the dragonfly squadron calls over his headset as they approach the Sterling flats west of the Kenai Mountains, "This is Blue Leader, approaching target; everyone ready? "
"Roger, Blue Leader," one by one the squadron calls back.
"We'll do the same maneuver as before but this time we'll work the south side of the highway. Wingman, you'll go first."
"Roger, Blue Leader," the Wingman calls back, "I'm salivating already. They don't call us the Pollywog Marauders for nothing."
As they come to the highway, the squad slows and tightens formation. The drone of the hovering dragonflies spreads panic through the potential prey below. All are hoping their camouflage or quickness will keep them from the dreaded predators circling above. All, that is, except the dimwitted tadpoles that live near the road.
According to studies on the Kenai National Wildlife Refuge, copper toxicity and pesticides have led to a significant proportion of deformed frogs. In the case of copper, the culprit is brake pads that are made of softer material than the brake disks, usually involving copper. Every time you apply the brakes, friction slows your car and a little copper dust settles onto the highway.
The well-traveled highway accumulates copper brake dust from hundreds of thousands of vehicles that travel the road yearly. Think of the Sterling Highway in July with miles-long strings of traffic accelerating and braking as vehicles maneuver for position to gain precious minutes on the Kenai or Kasilof fishing grounds. Rain and melting snow wash the copper dust into the ditches, where, if there is a bog or stream, aquatic animals ingest some of it.
In humans a little copper is necessary for proper neurological function, among other things. Human copper toxicity happens when the body can't expel excess copper and it builds up first in the liver, then in the brain. The body has an intricate mineral ratio system: When one goes down, its counterpart will increase to take up the function. Zinc and copper are partners in numerous functions, including reactions to stress and adrenal function. Stress reduces zinc levels and copper replaces it. In the short term, copper can be involved in reactions acting as a stimulant bringing energy back to normal levels. But if long-term copper toxicity occurs, the mind is racing while the body is fatigued, and causes an increase in stress.
Something like this appears to happen with tadpoles. Experiments placing tadpoles in water with high copper concentrations led to lethargy. And tadpoles stoned out on excess copper can't get away from marauding dragonflies as well as their non-copper-toxic relatives. Consequently, near highways on the Kenai Peninsula there are a high number of frogs with limbs missing, the result of dragonfly predation during the tadpole stage.
"Wingman, this is Blue Leader. Do you see that slow-moving tadpole at five o'clock?"
"Roger, Blue Leader, I'm on him."
The wickedly efficient killing machine breaks from formation and dives approaching 50 mph. Below, the stupefied tadpole is vaguely aware of danger as nearby insects scatter. It reacts too late, and, bam, the dragonfly takes a chunk out of what would have been, after metamorphosis, the frog's leg. Tasty.
As the satisfied dragonfly returns to formation, Blue Leader says, "Nice job," and another moves up to take her place. After a few minutes, the dragonflies return with full bellies to their home base, where they will rest and return to the Sterling Highway feeding frenzy another day.
If copper brake dust affects amphibians, it probably affects fish as well. Two states, Washington and California, began phasing out copper in brakes in 2010, and similar bills have been introduced in Rhode Island, New York and Oregon. The legislation requires copper to be replaced by synthetic substances. It also requires brake pad manufacturers to reduce asbestos, cadmium, chromium, lead and mercury to minute amounts.
While all aspects of the environment, even tadpoles, are a concern, we should be especially concerned about the effect of copper toxicity on salmon. For the sake of our tadpoles, our salmon and ourselves we should join the movement to phase out copper in brakes, the sooner the better.
Alan Boraas is a professor of anthropology at Kenai Peninsula College.