A new study has found that two species of predatory cone snails use insulin as a weapon to kill their prey.
When the snail approaches a fish, it releases the insulin, which enters the fish's gills causing its blood sugar levels to plummet. This results in a sudden drop in energy, effectively paralysing the victim, so that it is unable to swim away.
Scientists from the University of Utah found that fish insulin was present in the venoms of Conus geographus and C. tulipa, which both practice the same fish-trapping method of releasing a blend of immobilising venoms into the water. After immobilising its prey, the snail protrudes a stretchy mouth-like part and aims it like a gun barrel at the fish, before this mouth part slowly advances and engulfs the victim.
But the Utah researchers found no evidence of fish insulin in the venom of five species of fish-eating cone snails that are ambush hunters that attack with a harpoon-like organ. Nor did they find fish insulin in the venom of cone snails that prey on molluscs or worms.
The study appears in Proceedings of the National Academy of Sciences.