Snakes bite. Some just stay pissed off. I have a big firefly male that has been pissy since he was a baby. Hes tagged me more times then i can count. Hes just always mad. I have some that are great and chill and others that are just nippy. The fact that hes aggresive will usually mean a good eater. Considering they are an animal that likes to be left alone he may just not want to be messed with. Dont be scared of him. Just reach in and grab him. He will either get over it or wont. As long as your husbandry is good which it appears to be and hes eating and the plumbing works good i wouldnt worry too much. The mites could have pissed him off too. I know if i had mites on me id be upset.