subterranean Spixi snails

OK, something weird is going on here...
my adult Spixi is digging in the gravel :eek5:
I never noticed this behavior in any snails*.

so today I did an inventory of my 7 adult
Spixi's, and found 4 of them completely
buried in my gravel about a CM down.
they were isolated, and not attached
to anything in particular, with their
pop top lids tightly shut. when I took
them out of "hibernation" they opened
up and explored as usual.

what the heck is going on?!



*accept MTS, obviously...