People often forget that under severe stress or excitement behavioral communication often breaks down resulting in abnormal behaviors in captive animals. As an example, there have been anecdotal reports for a long time from people working with groups of toads where feeding would excite the males enough that they would initiate amplexus (I've seen this with both Wyoming toads and Southern Toads) attempts.Frog was immeditately pulled and put with another Regina in a diferent tank. We watched the tank like a hawk. Within 2 minutes, they moved to the center of the tank nose to nose for a stare down at the OK Corral. The owner didn't want to risk it and pulled the frog yet again. Now all three are housed seperately.
I was shocked at the viciousness of the attack. Worse, it took place less than six inches from a water feature. From someone who has never witness blatant aggression, it was quite surprising. We tend to think of our frogs as these cute, happy-go-lucky pets. It's clear that they can be stone cold killers!
Anytime you deal with a species that defends reproductive resources and add a new animal to the group you have to expect aggressive behaviors as the animals work out home ranges. If the goal is to have them together then removing the animals and housing them together for awhile can help but you have to able to do this long enough that the territorial cues for the resident animal is lost.