Sudden Ant Death on Tomatoes

[peebee]

This is really weird. I have a vegetable in-ground bed at my workplace with about 20 tomatoes growing, all healthy so far. On only one plant I noticied several ants crawling all over the top this past Thurs as I was leaving. Decided to inspect closer for possible aphids the next morning (yesterday). Imagine my surprise when I see lots of tiny dark spots on the leaves, so I think AHA! Those are the culprits...but when I look closer, I realize they were all dead ants! Not a single one was alive or walking around now. No one has access to insecticide, its a small company and only one more person really tends to it besides me. There are only warehouses nearby, not densely spaced at all, and this happened overnight so I know there was no yard maintenance going on to explain this sudden death.

What could be a possible explanation? There is no damage to the leaves or plant in question, just these shriveled ants. No aphids or anything anywhere, over or under the leaves.

Puzzled