Are these 'crabs' destroying my bird's nest?

[parkinsn]

Hairy legs generally = bad. I would flush/sump them/give the to some one with a trigger. you should be able to get them out fairly easily with a pair of tweezers.

[kevNnic]

pretty neat looking crab, i had a hitch hiker like that when i purchased some LR, ended up dieing looked alot like yours there. i'd put them in the sump.