Image: Warrior worms
Ryan Hechinger
Sept. 14, 2010 — One worm (left) consumes his rival. The eyes and innards of the rival are visible within the insides of the attacker. Trematode flatworm parasites exist in cooperative colonies consisting of big reproducers, which release hundreds to thousands of clonal offspring daily, and specialized soldiers that defend the colony.
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updated 9/15/2010 12:37:33 PM ET 2010-09-15T16:37:33

Some worms are far more socially complex than thought, according to scientists who have just discovered one species that forms social castes, including armies of warrior worms.

The study, published in the latest Proceedings of the Royal Society B, is the first to determine that any worm lives in a colony with organized division of labor. In this case, trematode flatworm parasites exist in cooperative colonies consisting of big reproducers, which release hundreds to thousands of clonal offspring daily, and specialized soldiers that defend the colony.

"The soldiers use their relatively large mouth parts to bite enemies," lead author Ryan Hechinger told Discovery News. "They sometimes swallow enemies whole."

"Soldiers sometimes rip open the body wall of the enemy and then suck out the insides," added Hechinger, an assistant research biologist at the Marine Science Institute at University of California, Santa Barbara. "You can sometimes see the eyes of the enemies' progeny inside the soldiers' guts."

He and colleagues Alan Wood and Armand Kuris collected California horn snails infected with the flatworm colonies. They analyzed both the physical appearance and behavior of the parasitic worms, including how the flatworms reacted when rivals were present.

The warrior flatworms stayed together in armies and maintained small, sleek and active bodies. Despite being 60 times smaller than reproducing flatworms, their jaws were just as big.

"It's good to be small for the soldiers because they can travel to areas of the host body where new invasions enter, so what we had was selection for a division of labor," Hechinger said. "Some individuals specialized in reproduction, becoming relatively immobile, fat slugs pumping out progeny."

The scientists think the worms started out as generalists. But as onslaught from invaders increased, traits evolved in some worms that benefited defense, while the reproducers became more specialized at what they do best.

It's now thought that all 20,000 or so trematode species live in such organized colonies.

Their cooperative societies appear to be extremely successful. Each colony lives for at least a decade, and the individual worms appear to live for quite a long time too.

"We say that because we don't generally encounter dead or dying worms," Hechinger explained. "In this study we carefully looked at 91,229 worms from 51 colonies and never detected a dead or dying worm."

In the future, the soldier worm armies may benefit humans, too.

"Hundreds of millions of people are infected by blood flukes," he said, adding that flukes (a common name for trematodes) can also attack the liver and lungs.

"Trematodes with soldier castes have a biomedical application because they may be used in the biological control of these problematic parasites," he continued. "Soldiers may also help to keep human disease-causing trematodes out of snail intermediate hosts, preventing infections in humans."

Bernard Crespi, a professor of evolutionary biology at Simon Fraser University, told Discovery News that he completely agrees with the new findings and "was astonished" when he read the paper.

"Such discoveries of sociality are quite rare and special, in providing new systems for testing theory and understanding how, why and where sociality has evolved," Crespi said.

Parasitic flatworms now join snapping shrimp, sea anemones, mole-rats and a handful of others on the relatively short list of organisms that form similarly organized castes.

© 2012 Discovery Channel

Explainer: Eight insects with the 'ick' factor

  • Warren Little  /  Getty Images file

    Many insects provide humans with unheralded services such as pollination, sustenance, and pest control, but some of them gross us out — or worse. Take dung beetles such as the one shown in this image, for example. As their name implies, the insects process feces for their livelihoods. The service helps reduce fertilizer costs on grazed agricultural lands and cuts down on the number of flies and parasites the piles of manure would otherwise attract. But a life of dung? Ick.

    Click the "Next" arrow above to learn about seven more insects with "ick" factors that make us squirm, or much worse.

    — By John Roach, msnbc.com contributor

  • Head lice, the annoying itch

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    For moms and dads, the thought of head lice can sow panic at home. School-age kids are prone to pick up the feared infestation of the sesame-seed sized insects in packed classrooms. The critters latch onto hair follicles and feed on tiny drops of blood. At first sight of head lice, many school nurses send infected — and itchy — students straight home. And that's when parents freak out, lathering their kids with shampoos, gels and creams in an effort to kill the lice. However, some lice are proving resistant to the treatments, leaving parents scratching their heads over what to do.

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    The "how cute" reaction evoked by scenes such as the one shown here can quickly change to "ick" when our dogs start gnawing on their fur to rid themselves of fleas. The wingless, blood-sucking insects can also be more than an itchy nuisance: they are known to spread bubonic plague between rodents and humans, which has killed millions of people. Experts recommend frequent vacuuming, regular washing of pet bedding and treating household pets with topical insecticides.

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