Why is the UC Irvine mascot an anteater?

You've been dying to know! 8-)

Here is the story of how UCI got the anteater as a mascot.

In brief:

The Anteater was nominated based on Johnny Hart's comic strip B.C. and won by a landslide, partly due to a one-man political campaign by a student named Schuyler Hadley Basset III, and partly due to two of Irvine's first Water Polo players, Pat Glasgow, & Bob Nealy whose idea it was to use the Anteater.
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A water polo game against San Luis Obispo took place just before the mascot election and shortly thereafter, on Monday, November 29, 1965, the student body voted 56 percent to adopt the anteater as the official mascot.