Try soaking him in a tub with water for a while. Mites drown easily under water ;-) It worked on me before! Just make sure the water is nice and warm and that the snake doesn't drown along with the mites @_@ ( I must say though, boas can hold their breath under water for quite a long time! ) Don't forget to towel dry so it's not soaking wet when you put it back! She could get an RI @_@