MAINZ, GERMANY — Eternal youth is the first thing many of us might wish for if we stumbled onto a genie, but there's always a catch. Now, scientists have discovered a version of this story playing out in ant nests, as parasites drastically extend the lifespan of worker ants — but at a terrible cost.

Researchers from the Johannes Gutenberg University in Mainz studied T. nylanderi ants that were infected with A. brevis tapeworms and found that the infected ants lived longer.

They found that's because the tapeworms release chemicals that keep their victims young. Even at an advanced age, the infected ants still retained their youthful bodies.

Young ants start off a yellow color, usually turning brown as they age and their skin hardens — but infected ants stayed yellow.

The infected ants were also very lazy, never leaving the nest or helping with any of the usual tasks.

The tapeworm chemicals also seemed to change the behavior of the ants around them, as these uninfected ants would serve them as if they were queens.

Researchers think the tapeworms release the magical chemical in their hosts because it makes them too slow to move away when birds break open the ant nest to hunt ants.

In this way, the tapeworms get swallowed with their hosts, which leads to the worms' eggs getting spread over large areas when the birds defecate.

On closer inspection, the team found some metabolic changes in infected ants that drive this biology and behavior.

When worker ants are promoted to become queens, certain genes switch on that boost their lifespan — and the worms also seem to be able to turn these genes on in their hosts.

Infected ants also give off unique chemical signals that drive the other ants to want to look after them.