<unk>  is a somewhat unusual, but medically well-known, abnormal sensation. This sensation closely resembles the feeling of insects crawling on and/or under the skin, and can also include sensations which resemble those of insects stinging or biting. There are many known causes of<unk> .
The word is derived etymologically from the Latin word formica, meaning "ant", precisely because of this similarity in sensation to that of crawling insects.<unk>  is a specific form of the general set of abnormal skin sensations known as paresthesia, and thus it is related to the sensation known as "pins and needles", and other tingling sensations.
Some people suffering the sensation of<unk>  find it to be annoying, others find it painful, and some find it itchy. Those who find it to be itchy may in some cases repeatedly scratch themselves until they bleed, causing skin damage and sores. (In the subset of cases where the sufferer is delirious or intoxicated because of high fever, substance abuse, or extreme alcohol withdrawal, this repeated scratching is very common indeed.)<unk>  can on occasion lead to people becoming fixated on the sensation and its possible meaning, and these people may develop delusional parasitosis. This is a situation where individuals are convinced that there are real insects crawling on and/or under their skin, whereas in reality there are no insects involved, just a crawling sensation. It is fairly easy to misunderstand the significance and causality of the "creepy crawly" sensation of<unk> .
Formication
Staining
Reading
Splitting 
Induction 
Acting out
Canning
Exaptation