This definition goofed in not mentioning that the "form-"
refers to ants.
formication
For`mi`ca´tion
Noun 1. formication - hallucinated sensation that insects or snakes are crawling over the skin; a common side-effect of extensive use of cocaine or amphetamines

And defintion also goofed in saying it is "hallucination".
It is usually an illusion, a misinterpretation of itching
from contact dermatitis, etc.