On "Whitmonday," Bloom thinks in Calypso, "That bee or bluebottle here" (. . . did something or other). In Lestrygonians the reader learns what it did: "Still I got to know that young Dixon who dressed that sting for me in the Mater." Bloom was stung in the garden area behind his house on May 23.
Whitmonday is the day after Whitsunday, which falls on the seventh Sunday after Easter. Gifford notes that it is a bank holiday in Ireland, which suggests that Bloom may have been enjoying himself at home at the end of a three-day weekend when the incident occurred.
Many people would remember a bee having stung them three weeks earlier, but not many (unless they were severely allergic) would run to the nearby hospital to be treated by a doctor. Bloom's babyish alarm confirms what Molly thinks about him in Penelope: "if his nose bleeds youd think it was O tragic." It is the subject of hilarious parody in Oxen of the Sun: "the traveller Leopold came there to be healed for he was sore wounded in his breast by a spear wherewith a horrible and dreadful dragon was smitten him for which he did do make a salve of volatile salt and chrism as much as he might suffice." (One can make such a chrism for oneself, at home, with baking soda and water.)
In addition to earning him the name of wimp, Bloom's reaction to the incident betrays a lack of entomological curiosity. Bees sting, but the bluebottle does not. Only slightly larger than a housefly, it possesses very similar anatomy and behavior.