St. Patrick's Day seems to be universally beloved. I can find no historical links between St. Patrick and cats, but judging by the abundance of cat blogs celebrating the day, I'd say there is definitely some sort of nexus. Here is just a smattering of "St. Catrick's" blogs I found:
33 Cats Celebrating St. Patrick's DayFats, pictured here in Irish surroundings, is one of the cats in our 2009 March Tabbies Picture Gallery.
St. Patrick's Day for Cat Lovers
Photo Credit: © Doris J. Brookes
St. Patrick's Day on About.com