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Scientists reveal secret to tropical worm's slime attack

Many animals employ a spitting or spraying technique to hunt prey, but most require some level of manipulative control -- the worm opts for a more thoughtless approach.

By Brooks Hays
Scientists reveal secret to tropical worm's slime attack
The velvet worm shoots slime out of its head to trap prey. Photo by Cristiano Sampaio-Costa/Andrés Concha/Harvard

CAMBRIDGE, Mass., March 18 (UPI) -- If you think Nickelodeon invented the slime attack, think again. The slime attack originated as a much more sinister deed, carried out by an unassuming tropical warm -- not as a way to embarrass unassuming game show contestants on live television, but as a method for trapping a meal.

The velvet worm -- a long and slow-moving worm that likes to hang out in damp logs in tropical climes and looks more like a slug -- has a secret weapon. When it's dark, the worm traps its prey using two jet streams of a sticky, slime-like substance. The slime attack traps unsuspecting crickets and termites, leaving the worm's dinner stationary and incapable of fighting back.

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But how, scientists have wondered, does such a simple worm with such a small brain execute such a sophisticated hunting technique?

New analysis by researchers at Harvard University has revealed the worm's biological strategy in great detail. High-res imagery helped scientists model the worm's slime-shooting apparatus. The slime originates at the tail, and is squeezed forward. The system is like a large syringe with a corrugated tip, which causes the quickly squeezed slime to shoot out in all directions (like a shotgun shell), forming a net of slime.

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The pair of tiny nozzles through which the slime exits are called papillae. The slime is produced and stored in a reservoir in the tail, and a slow, gentle squeeze is all it takes to send the slime gushing forward.

"After watching the David Attenborough film Life in the Undergrowth with some high-speed footage of the worm's slime jet, I suggested that an elastic-hydrodynamic instability of the nozzle could be a simpler solution to creating a chaotic jet, rather than muscle control," study co-author L. Mahadevan, an evolutionary biologist at Harvard, explained in a press release. "Our work shows that this is indeed the case, and chalks up one more example of how evolution has co-opted a simple physical principle for a behavioral response."

Many animals employ a spitting or spraying technique to hunt prey, but most require some level of manipulative control -- which, in turn, requires a higher degree of neurological complexity. The velvet worm, however, has found a way to spray accurately and effectively without really thinking.

The new study was published this week in the journal Nature Communications.

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