One hatch to rule them all

Epic mayfly hatches close bridge, cause numerous motorcycle accidents
mayfly hatch bridge closure susquehanna river route 462
A swarm of mayflies hovers over the Route 462 bridge over the Susquehanna River late Saturday evening, June 13, 2015 (Blaine Shahan/LNP via AP).

Pennsylvania, one of the nation's heralded trout fishing states, has always been known for its bountiful mayfly hatches. But fishermen telling tales of "epic" hatches may have a new yardstick to measure their stories against, after hatches in Lancaster County resulted in numerous motor vehicle accidents and caused officials to enforce bridge closures for the second night in a row.

The hatches seem to be predominantly hexagenia mayflies, though photos circulated on the internet seem to show other mayflies and stoneflies present as well.

Every angler dreams of hitting it just right, concocting fantasies of being there the night the "blanket" or "blizzard" hatch goes off, casually tossing dries to eager, blissfully feeding trout, reeling in one fine specimen after another. Those fantasies, however, don't normally include mayfly swarms so thick that flies choke angler's mouths and stick to their eyes, cyclists are tossed from their bikes and dead flies are deposited in thick layers and drifts which waft of dead fish.

The swarm that first hovered over route 462 bridge over the Susquehanna River on June 13 was described by numerous observers as "unbelievable." The conditions were hazardous for motorists, and resulted in three different motorcycle accidents. The swarm reportedly resulted in zero visibility for as much as a quarter mile and the several-inch thick layer of mayflies that coated the bridge's surface created driving conditions that drivers described as "ice-like."

After police and emergency officials responded to the initial motorcycle accident and observed two subsequent accidents while on site, they determined conditions on the bridge to be unsafe and closed it to vehicular traffic. Conditions the following night were much the same, prompting additional closures.

route 462 mayfly closure
Mayflies coat an emergency response vehicle (photo: Tim Coover).

To be clear, true "blizzard" hatches are nothing new. This isn't the first time mayfly swarms have wreaked havoc on motorists and Wisconsin has had hatches so large they appeared on radar as rain. But this most recent hatch may indeed be one to be remembered, due to its sheer volume and intensity. One observer standing riverside even reported that he "saw and heard several significant sized limbs broken off by the sheer weight of the hanging mayflies."

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