If you’ve ever looked at ant cocoons, you may have noticed they always have a dark spot at one end:

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Lasius alienus – brood nest showing stained cocoons (Illinois).

What’s up with the spot?

There is no way to put it delicately: it’s poop. The dark spot is at the butt end of the developing ant. But this spot is not just any old poop. It’s a rather special one called a meconium.

Although young ants have been alive and eating for many weeks by the time they spin a coccoon, they never once passed their food all the way through. Ant larvae are massively constipated. Their waste builds up in the digestive tract as a strong, concentrated mass clearly visible through their translucent bodies:

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Ochetellus sp. (Victoria, Australia)

Larvae hold the pellet in as it gets larger through several molts, and don’t expel it as a meconium until they transition to the pupal stage. So, young ants only poop once.

Of course, there is good reason for the extended constipation. Living in large groups in fixed nests, ants have a public health interest in not continuously soiling their nurseries.

Speaking as an expectant father myself, I admit to a little bit of jealousy of a species that manages but a single diaper change per offspring.