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3. Cant figure this out...

I wouldn't even bother to ask this if it weren't for what happened yesterday. Last week the sulphurs started popping up on the lower Delaware which is exactly one mile from my home here in PA. I work 2 miles from the river in NJ, right across the river from my house. When the sulphurs are up, we get them all over the exterior of the shops walls as they are attracted to the gas stations lights. I can understand this, as they can probably see the illumination from the river in their mayfly eyes. The thing that I don't understand is this...

Coming back from my fathers house which is 7 miles from the river, a 2 lane road was literally swarming with sulphur spinners, most with eggs, for a distance of over 3 miles in length. This road does not have any streams close by, except for 1 tiny runoff stream that is dry from July to February.

How do these hundreds of thousands of mayflies make it 7 miles from the river? Does the wind carry them? It is so odd to see, they mistake the road for the stream during rainy periods which I see on roads that parallel streams but never when they are so far away from them. I just don't understand this!

What do you think? CJ

I've seen spinners over wet roads too. But I can't say much about distance from a watercourse. Maybe there is a stream near the area you aren't aware of? Check Google Maps and look for streams.

Spinners are known to travel, apparently upriver according to research, an adaptation in which adults seed upstream reaches that allows for downstream drift of larvae. But how far are they known to travel and will the leave the natal watercourse?

I have seen (and suspected) spinners quite high over the tree tops, so its possible swarms could get blown off course. I think these high swarms may be males only though, I seem to recall, and females join later. Anyway...

I dunno. Check a map of the area and look for other water courses. I've known some small fertile farmland streams that crank out a lot of sulphurs.

First read this as a primer on polarotactic water insects.
http://jeb.biologists.org/content/207/5/755.abstrac

Then this on asphalt surfaces:
https://www.novapublishers.com/catalog/product_info.php?products_id=18709

Thanks Falsifly!

This line is great...
Polarotactic insects mistaking asphalt surfaces for water bodies lay their eggs upon dry asphalt after copulation, where the eggs perish due to dehydration.
Ya think?

As a side note, I have never seen this happen on dry roads, even next to the water, only during wet road conditions.

I guess my question was not so much why they are attracted to wet roads, that makes sense, its how did they get 7 miles away from the river in the first place?

Appreciate the info, you college educated dudes are smart! CJ