I started with two hermit crabs, and they would run through the normal hermit crab cycle of not being out much during the day and being more active at night. Recently, one of my hermit crabs died and, as unfortunate as that is, I have begun to see a lot more activity in my other crab. I'm not so concerned, I'm just wondering why this spike of activity has happened directly after my first crab's death. Is he lonely, or is he maybe looking for my other crab?
Hermit crabs are known to fight, so this might be a result of it feeling safer now once the other one is gone.
Lots of crustaceans have problems living close to each other, and one can see this in crabs-crayfish-lobsters; they will fight and hurt each other.
So your hermit crab does probably feel safer now and this is why it is more active now.