they are definitely a pretty aggressive eater, caought them many times, and they eat just about anything that floats by,
as mentioned, they are a member of the scorpions (i believe), there are seveeral species and some do have spines that are reported to be venomous, i ma not sure which one or ones are found in this hobby to tell if that particular one is venomous or not
they are neat thouhg, the way they walk and grunt, and are very adaptable as far as temperature, and can be found in greatly varying temps of waters
i have caught them over 12 inches, and have read that they do get up to 15 inches in the aquarium
HTH