I happened to read about this today: the ants are just COLD!
Why they would be out and about then to SUFFER the cold, remains a mystery to me too. Let's wait till all the other responses pile in for this to be solved promptly by our formica-savy fellow Steemians.
What's the meaning of "formica-savy"?
Formica is Latin for ant. Savvy is (above) shamefully misspelt, but means, shrewd and knowledgeable.
The mystery then continues! Doped up on sugar remains my second best bet. Or, no, that would make them hyper, wouldn't it? Dying from an antacid then (anti-acid: as a child, squishing the words together and twisting them apart in multiple ways, I used to think that antacids were used against ants)?
Aha! Now I know why that acid (in high school chemistry lesson) was called formic acid.
Maybe it was just a normal gathering for an anniversary. Who knows...!