Recently I purchased 2 African dwarf frogs. One didn't make it very long and the other seemed to be doing very well. After the first one died the other one seemed lonely and less active so I figured I would get him some company. I purchased 2 more African dwarf frogs about 10 days ago and things seemed to be going well and he was becoming more active again. Today I got home from work and one of the new ones(probably the same one I saw going after my snail) had bitten the leg of my original one! Are they generally aggressive? I've never seen them like this and I thought they preferred groups?