Cone snails are known for their venom. Upwards of fifteen people have died of it. One snail, Conus geographus, doesn't even have to sting to kill its prey. And scientists have found out why.
To fill someone with poison you'd need a claw, a fang, or stinger, right? Not if you're Conus geographus, the geography cone snail. The snail does have a tooth that it can use to inject venom into animals, but it can also just release its venom into the water and open wide. The cocktail of toxins disorients the fish until the snail can just swallow them up.
Researchers at the University of Utah looked at the gene sequences that produced the many toxins in the cone snail, and found genes that seemed to code for the hormone insulin. It was a more compact form of insulin than that which humans and vertebrates use, but it was insulin. When injected into a fish it caused a fast and dangerous drop in blood glucose levels. When blood glucose goes up after meals, insulin causes the body's cells to accept the glucose, fueling the cells and dropping the level of glucose in the blood back down. This system needs to be tightly regulated. Diabetics, who don't produce enough insulin, get dangerous spikes in blood sugar levels. Hypoglycemics have too little blood glucose, sometimes from producing too much insulin. Depending on severity, hypoglycemia causes confusion and agitation, unconsciousness, seizures, and death.
Being injected with the insulin gave a fish hypoglycemia, but fish that were simply in the water with the insulin also stopped swimming properly. The researchers estimate that the snail could, if it wanted to, take out a whole school of fish with its venom.
This hormone is not the only dangerous protein in cone snail venom. Conus geographus, for example, also seems to have venom components that target human pain receptors - because if nature intended for us to get into a body of water without fear, she would have had Peter Benchley and Steven Spielberg eaten by a shark before they created Jaws. Of this arsenal, the insulin might be the key ingredient that catches the snail its dinner. And knowledge of a very compact form of insulin might come in handy someday for humans as well.
Images: Jason Biggs and Baldomero Olivera