There are a number of things for which one is ipso facto excommunicated without being canonically, juridically excommunicated. From the Catholic Encyclopedia:
"Excommunication, especially a jure, is either latæ or ferendæ sententiæ. The first is incurred as soon as the offence is committed and by reason of the offence itself (eo ipso) without intervention of any ecclesiastical judge; it is recognized in the terms used by the legislator, for instance: “the culprit will be excommunicated at once, by the fact itself [statim, ipso facto]”. The second is indeed foreseen by the law as a penalty, but is inflicted on the culprit only by a judicial sentence; in other words, the delinquent is rather threatened than visited with the penalty, and incurs it only when the judge has summoned him before his tribunal, declared him guilty, and punished him according to the terms of the law. It is recognized when the law contains these or similar words: “under pain of excommunication”; “the culprit will be excommunicated”.