Here is an ocean of butterflies, 70 miles wide, captured on radar over Colorado
https://www.dailykos.com/stories/2017/10/6/1704785/-Here-is-an-ocean-of-butterflies-70-miles-wide-captured-on-radar-over-Colorado?detail=emaildkreAn enormous migration of painted lady butterflies was captured by a Denver weather radar. There are more images, which you can see on the Denver Star, and they are pretty extraordinary. It was so extraordinary that the first person to see the 110 kilometer (68.35 miles) spread wasn’t sure what he was looking at.
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OAKLAND, CA - APRIL 11: A Painted Lady butterfly rests on a flower April 11, 2005 in Oakland, California. The heavy rains that pounded California over the winter have resulted in bumper crops of both thistles and wildflowers throughout the state and are attracting millions and millions of migrating Painted Lady butterflies that lay their eggs on thistles and, as adults, avidly feed on the nectar of a wide range of wildflowers. The last similar migration was in the spring of 1992, which also followed a particularly wet winter. (Photo by Justin Sullivan/Getty Images) The painted lady butterfly
Paul Schlatter of the National Weather Service said he first thought flocks of birds were making the pattern he saw on the radar Tuesday, but the cloud was headed northwest with the wind, and migrating birds would be southbound in October.
He asked birdwatchers on social media what it might be, and by Wednesday had his answer: People reported seeing a loosely spaced net of painted lady butterflies drifting with the wind across the area.
Schlatter said the colours on the radar image are a result of the butterflies’ shape and direction, not their own colours.
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They are everywhere around here! It's like walking through a butterfly sanctuary. Now I finally know what is going on. Thanks 
As I was walking to my car in Aurora, I saw a butterfly victim on the ground. It looks like some of them did not make it out in time for the snow. 
So sad to find that. They all look so happy flitting around the gardens for weeks.
...is the term for a group of butterflies.
almost as large at this suggests -- with some help from us, not bushhogging until well after it's gone to seed. It's not exactly rampant and it's also a host for Monarchs. Asclepias tuberosa grows and blooms from underground tubers so is slow from seed while the tubers develop and touchy to transplant, so buying smallish starts from a nursery can be a good way to go.
We also have Asclepias syriacus, "common milkweed," at the bottom of our little meadow, and it spreads rampantly underground. We like it, but then we're not doing anything else with that land.
I've read that Asclepias curassavica "tropical milkweed" is the Monarch's big favorite by far, but it has to be grown as an annual in most of the U.S.
Btw, relatively few Monarchs here in north Georgia, but one of our big yellow butterflies is migrating now, so almost every glance out the window shows at least one or two zig-zagging south, stopping briefly as flowers are spotted. Wild asters, salvias, sedums, butterfly bush, perovskia, goldenrod are some still in bloom for them now after a hot, lately dry summer in Georgia.
