Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
formīcātĭo, ōnis, f. [formico], an irritation of the skin resembling the crawling of ants, produced by pustules; Gr. μυρμηκία: corporum, Plin. 28, 7, 20, § 71; Cael. Aur. Tard. 5, 1, 2: eorum articulorum, qui tanguntur, id. ib. 5, 2, 30.