As how Mio was when she was the "Black Spider of Calamity", the Arke's were also suffering from extreme starvation and were driven insane by it and with almost no escape. But thanks to Mio giving Makoto's energy to them they have returned to their senses.
Arke's can produce special material inside their bodies. They are also extremely intelligent and highly adaptive and have knowledge of alchemy from ancient times and are also good at identifying, taking care and production of plants and herbs with medicinal value. They are also skilled at learning various types of Magic, such as Transformation, that allow them to take a Human form.
The Arke's who came to Asora amounted to a total of four unnamed individuals, who were later given names by Makoto,