Zoologger is our weekly column highlighting extraordinary animals – and occasionally other organisms – from around the world

Jim van Belzen

Species: Ragworm (Hediste diversicolor)

Habitat: Sand and mud in the north-east Atlantic

Marine worms have been spotted growing sprouts in their burrows, a type of cultivation never seen before in animals other than humans.

Ragworms (Hediste diversicolor) were thought to consume the seeds of cordgrass, an abundant plant in the coastal habitats where they live. But the seeds have a tough husk, so it was a mystery how the worms could access the edible interior.


Zhenchang Zhu at the Royal Netherlands Institute for Sea Research in Yerseke and his team have now discovered the worms’ surprising trick: they bury the seeds and wait for them to germinate, later feeding on the juicy sprouting shoots.

The worms have a varied diet. They prey on small invertebrates and suck up plant debris from soil, the most abundant source of food in their environment.

But sprouts, which are rich in protein, fats and amino acids, are more nutritious, even compared to the raw seeds. “The process of sprouting improves the digestibility and quality of the food,” says Zhu.

Zhu and his team think the ragworms started cultivating sprouts partly because of a lack of high-quality food sources in their habitat.

To test the effects of sprout consumption, they gave 20 worms different diets. Although the worms were initially about the same size, those that ate sprouts gained more weight, growing by 25 per cent, compared with 5 per cent for those that stuck to raw seeds and sediment.

Key to survival

Ted Schultz, an entomologist at the Smithsonian Institution in Washington DC, thinks that sprout cultivation could be important to the worms’ survival, and that this is a sophisticated adaptation because they must wait to harvest the food rather than consuming it immediately.

“The behaviour will likely be favoured by evolution, and future generations of ragworms will also store seeds and reap the deferred benefits,” he says. “It’s the beginning of agriculture.”

Ragworms are not the first animals to take up farming. Some beetles, termites and ants have cultivated fungus since long before humans started growing crops. And there are likely to be further examples: Zhu and his team think the ragworms may be cultivating bacteria in their burrows as a source of food, too.

The researchers also suspect that earthworms could be sprout-growers, because they are thought to supplement their diets with seeds. “They have similar problems finding high-quality food,” says Zhu.

Journal reference: Ecology, DOI: 10.1002/ecy.1613

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