Gather them...start a large pot...add some "Old Bay" seasoning....well, I think you can take it from here! LOL!

Okay, sorry for the joke. I was actually born in Texas (Gulf Coast region, Matagorda Bay area). These little castles go up as Texas gumbo mud and dry like concrete.

Best I can suggest is walk the yard like you do for limbs and dog poop, take a hoe or other long-handled tool with you. Knock them down and crush them with your boot so the blade of the mower doesn't hit them, or pick them up after you knock them off.

Due to the high water table, I woudn't try to put anything down the mounds to kill them. In my area of Matagorda County, the good drinking water was at 400-450 feet, but we still had surface water well above that shale/limerock layer. I don't like mixing things with water, other than tea and whiskey. The water you drink might be at 450 feet, but when you are 17 feet above sea level, that water goes somewhere.

Make it a game, get the kids some golf clubs and see who can slam the most castles the furthest distance.

And for those who don't understand, crawfish are not just in wet places. They make the deep tunnels to stay moist in the moist clay-like soil well below the surface of the dirt. The castle is like an "ant-hill", as it is material they dug out to make the hole deeper. As soon as things get drier, they dig deeper.

It takes a long time for clay a couple feet down to dry out, if it goes that long without rain.