Can ants that are two different sizes be from the same colony? (a reader, US Virgin Islands)

Dear AntAsk:

My sister lives in St. Thomas, USVI. She writes the following:
"I have ants sometimes walking across my sofa. Have you ever heard of two different sizes of ants working together? Mostly they are tiny, but there are quite a number, maybe 1 in 10, which are about 3 times as large. They don't act like they're on different teams, and they seem to lug crumbs along the floor together. Never seen such a thing."
Neither have I. Any thoughts?

Dear Owen (and Owen's sister),

Thanks for your question. What you're seeing is most likely an ant in the genus Pheidole. Pheidole megacephala is probably the most common ant seen in people's houses that has two distinct sizes (such ants are referred to as dimorphic). The larger workers, sometimes called "majors" or "soldiers" have huge heads, and usually stay in the nest, but will come out to help the smaller workers when a particularly delicious (high in protein and/or fat) source of food is discovered.

There are several groups of ants whose workers come in more than one size, or caste. Ants have workers that are continuously variable in size (like carpenter ants, genus Camponotus, and Solenopsis invicta, the Red Imported Fire Ant) , or have more than two castes (like many leaf-cutter ants, especially in the genera Atta and Acromyrmex ). Such ants are referred to as polymorphic.

I hope this helps!
Jesse Czekanski-Moir & the AntAsk Team

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