Eh! Thanks to Babs for sharing this link:
Crank bugs are sores caused by two things: the body rejecting meth toxins which are emited through the skin and hallucinations of insects crawling underneath the skin; a common side effect of meth use.
Addicts can severely injure themselves by obsessively scratching, digging or cutting their skin with their fingernails (which are havens for staph bacteria) or any number of implements or "tools" to remove the imaginary bugs.
Sores appear predominantly on the face and arms. Skin removal. bleeding and pus-filled sores, infections and permanent scarring are commonplace.