Notice how the slings have died? Not like the normal closed fist, I find that a bit odd, I think it is way too cold in their enclosure.
If the room temperature that they are being kept at is 12 degrees you say, then add all the wetness of that peat too that and your enclosure is probably around 10 degrees or less. :reallysick:

12 Degrees at the moment... What about at 2am in the morning. The temps probably dropped below 12 during the night...

Check the ventilation, just personal experience

If they wore molting they would be in their webbing or on molting mats.
If it is indeed the cold then they would not be on their backs, as they just go stand where they are standing and battle to move. But again they would of been in their webbing.

If you look at the bottom right hand corner, there is a leg and then the other spider that is circled in black look like it is leaking.





The fact that all the spiders are on there back is not a normal why a spider dies.

None the less it is a strange why for them to die and all at the same time!
Chabendiv, where wore the other 3 spiders when you opened the lid?

Were they fed anything out of the ordinary? Like crickets from the garden perhaps?

My vote is also either cold or toxins.

HeteroScuderia wrote: Were they fed anything out of the ordinary? Like crickets from the garden perhaps?

My vote is also either cold or toxins.

Got my vote too