A. chalcodes sling behavior

[Frostbite]

I got 6 new 1/2" A. chalcodes slings last week. Each of them got a new 1" x 1" by 3" cube with coco fiber substrate and 4 small holes in the top for ventilation. I had noticed bits of coco fiber on the table but didn't think anything of it. This morning, all six had plugged the 4 holes in their cubes with substrate.

I've never had A. chalcodes before, (18 years of critters), and am wondering if this is some type of hiding behavior or what. They are from 4 different sacs. I think it's cool, but am curious.

Thanks in advance!