You've heard of blanket hatches. You may even think you've seen one or two. But the good folks of Kittanning, PA, would probably argue that you ain't seen nothing until you've witnessed the mayfly mayhem along the Allegheny River in July. This year, the annual invaders have piled up nearly a foot deep on roads and buildings. And after three motorcyclists dumped their bikes crossing over the river, town officials have decided to close the Kittanning Bridge. Still, the locals aren't complaining. "This time wasn't as bad," said the Fire Chief. "This was very light compared to what it looked like last time."