Scientists have found a parasite that can make an ant live many times longer, but only because it needs the ant to be eaten.
A parasite with a problem
This is the tapeworm Anomotaenia brevis. As an adult, it lives in the guts of woodpeckers. But to get there, it needs a middleman.
Its life cycle starts when tapeworm eggs leave a woodpecker in its droppings. Acorn ants, Temnothorax nylanderi, live in tiny colonies inside acorns and twigs on the forest floor in Europe. Workers collect the droppings as food and bring them home to feed their larvae. The eggs hatch inside the young ants and grow into a resting stage in their bodies.
Now the tapeworm has a problem. To finish its life cycle, its ant has to be eaten by a woodpecker. But an acorn ant worker doesn't live very long, and woodpeckers don't eat ants every day. If the ant dies too soon, the tapeworm dies with it.
So the tapeworm makes the ant live longer.
Workers that live like queens
Infected workers look different. They're yellow instead of brown, and they barely do any work. They mostly sit in the nest.
Sara Beros, Susanne Foitzik and their colleagues at the University of Mainz followed infected and uninfected ants in the lab for more than three years. They found that infected workers lived far longer than their uninfected sisters. In fact, their survival over three years was no different from the colony's queens, and acorn ant queens can live up to two decades.
The infected workers also stayed young on the inside. Their metabolic rate and fat stores matched those of young workers.
Pampered by their sisters
Part of the secret may be how the colony treats them. Infected workers received more care from their nestmates than other workers, and even more than the queen. Their sisters cleaned them and fed them.
That care has a cost. Healthy workers living in colonies with infected nestmates died sooner than workers from colonies without any parasites at all. The infected ants live like royalty, and their sisters pay for it with their own lives.
From the tapeworm's point of view, it's a perfect plan. A yellow, slow, long-lived ant that sits around in a nest is exactly what you want if your goal is to be eaten by a woodpecker.
Not the way queens do it
So how does the tapeworm do it? An obvious guess would be that it switches on the same genes that let queens live so long. But when Marah Stoldt and Foitzik's team looked at which genes were active in queens, healthy workers and infected workers, they found that infected workers don't seem to live longer by turning on queen-specific genes. The tapeworm appears to have found its own way to slow down aging.
Researchers are still working out exactly how. But that's what makes this parasite so interesting. It reveals that aging in ants can be changed, and that another organism can take control of it.
What a tapeworm can teach us about aging
Ants already break the usual rules of aging. A queen and her workers can have almost the same genes, yet the queen may live decades while her workers live a fraction of that. The tapeworm shows that even a worker's lifespan isn't fixed. Change its body and how its colony treats it, and a short-lived worker can live as long as a queen.
For scientists studying why we age, that's a big clue. And for the acorn ants, it's a reminder that a long life isn't always a gift. Sometimes it's just a longer wait for the woodpecker.
To learn how acorn ants fight other enemies, read about enslaved acorn ants starting slave revolts.
Further reading
- Beros, S., Lenhart, A., Scharf, I., Negroni, M. A., Menzel, F. & Foitzik, S. (2021). Extreme lifespan extension in tapeworm-infected ant workers. Royal Society Open Science.
- Stoldt, M. et al. (2021). Parasite presence induces gene expression changes in an ant host related to immunity and longevity. Genes.
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