Why do ants die after the queen dies?

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A fundamental fact about social Hymenoptera (wasps, ants) that most people, including entomologists, are unaware of: they cannot live without their larvae.

Next time you see an ant’s nest, a bee hive, a hornet’s nest, remember: that structure is essentially a neonatal ICU!

Why? Look at an ant’s body below:

Did you notice the waist? I tell you: the individual’s stomach is located after the thin waist. That means an ant cannot eat solids.

Now, take a look at an ant’s larva (a & b, below):

Notice the waist? There’s none. It means larvae eat solid food!

So, this is what happens: ants are working hard together in that nest mainly to bring up hundreds of babies. They come out to get food and bring it back to the nest, then they chew it up and place it on their larvae. Larvae will swallow and digest the food for them. Especially protein. Larvae secrete nutrient-rich liquids back to the ants, which is their main source of amino acids and fatty acids.

Who lays eggs to produce larvae? Queens*.

What happens when Queens die? No eggs, hence no larvae.

What happens when there are no larvae? Bad nutrition, ultimately no reason for the nest. Ants gradually get disorganised, after few weeks they die.

Cheers!

Notes: the same applies to other social Hymenoptera, such as wasps. Image credits: ant drawing from Clker.com, ant larvae drawn by Wheeler & Wheeler . [*] - Actually in many ant species, mainly within acidic-producing Formicinae, workers can also lay eggs and thus sustain the colony for long after queen(s) death.

P.S. Wasps and more ‘primitive’ ants can more easily produce a new queen who will be the next mated female in the hierarchy. However if none of them is fertile enough & mated, the nest won’t last long. Bees work differently.

Important technical notice: Queens normally live longer than workers. Nowhere in this answer I meant to imply that larvae can somehow enable workers to live as long as queens! (Some reader took it that way.)