there isn't really a safe size. Especially with one already that big. Some poeple do keep beardies together but it is not recommended. They prefer to have thier own space. In my own experience i had two juvi females who did well until out of nowhere one attacked the other. I was lucky that there was only minor injuries but i have heard of them having limbs bit off in fights. Again, they slept side by side until the one incident. not worth trying.
marilee
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0.2 Bearded Dragons (Dezirae & Artimis)
0.2 Dogs (Timex & Brady)
1.0 Sulcata (Speedy)
1.1 Hamsters
1.2 Horses (Joey, Joi & Crystal)
0.2 Beta Fish