they are very varied you get some destroyable in a few hits as lvl 30 but some can get up to being impossible so its better not to take the risk..and as for the crabs
party in la theine chaining them for lvls 11-14 is the best way
Ive been hunting these at the lake for quite awhile... One word of advice... If you see the water elemental that seems to pop up every now and then, DONT CAST SPELLS! If you do, DONT CALL FOR HELP! Just RUN! They take out level 40s like they are nothing, and they aggro by magic use... Ive seen too many people that get other parties killed by those...do everyone a favor...dont get them involved :P