Worried that the little mud piles I saw might be termites, I did some checking.
What the hell did I do before I had a broadband internet connection? What the hell did I do before Al Gore was "instrumental in the creation of the Internet"? It's like having a huge reference library at my fingertips whenever I want it. Man! This 21st century is pretty cool.
...anyway, I first googled "termites north america" and then, finding nothing that resembled the mud piles in the yard, checked "17-year cicada". Jackpot.
It turns out that cicadas don't go pupate. Their young are nymphs, like crickets. So they crawl around underground and feed off tree roots for 17 years. Then when it's breeding time, they come out, moult one last time, breed, lay eggs, and die.
The mud piles are what happens when they're getting ready to come out but it's not warm enough yet. When it rains, they push the mud to the surface, and otherwise they stay underground until--I am told--the soil temperature gets above about 64°F. So I am thinking that it'll be at least another two weeks before they start coming out, though that really depends on how the weather goes. If we have more 45°F nights like we have been having, it'll take longer than if the weather pegs on "summer" before the end of May.
Either way, it's kind of cool that I was right about the impending emergence of these bugs. (Also, it's really good that it's not termites.)
This will be the third emergence that I've seen; the first was 1973 and the second was 1990. I remembered almost nothing from 1973, but I'm pretty sure I remember 1990 well enough. It's going to get rather noisy in the next few weeks.