Milkweed Signals?

Watching for caterpillars as closely as I've been doing this summer, I noticed an odd phenomenon on the milkweeds about a week ago.

As of August 5th, last Sunday, I had not seen a single milkweed bug, large or small, on any of my milkweed plants this summer.  At midday, I was out in the backyard, photographing insects and flowers like the swamp milkweed above, when I noticed something reddish flying in the middle of the backyard. 

Chasing it down, I saw that it was a large milkweed bug (Oncopeltus fasciatus) which had landed on a small yaupon bush (Ilex vomitoria).  Note:  I apologize for the quality of this photo, but it's the only one I took at the time.

The next morning, August 6th, when I got up, there were probably a dozen large milkweed bugs on my swamp milkweed plants, primarily on the blooms.  Many were in the process of creating the next generation of large milkweed bugs.

In the space of 24 hours, my yard went from absolutely no milkweed bugs to a single large milkweed bug to a dozen or more large milkweed bugs.  The numbers have continued to increase over the week.

Where did they all come from?  No one else I see around the neighborhood has milkweed plants and there is little "wild space" nearby.

What brought them all in at essentially the same time?  The swamp milkweed had been blooming for over a week at that point, the tropical milkweed for weeks, and the butterfly milkweed for months, so why August 5th-6th?  Why that day specifically?

I have no answers to these questions, but it's a fascinating little mystery to me.  Sometimes it seems like the more I learn, the less I know.