A predatory shellfish uses a souped-up form of insulin to immobilise fish prey so it can capture them, a new study has shown.
Growing to over 20 centimetres in length, members of the cone snail family, which are found in the Pacific and Indian oceans, rank as the world's most venemous creatures.
They prey on fish and worms, which they capture using a deadly arsenal of neurotoxins injected into their victims down a harpoon-like structure called a radula. But now scientists studying two species of cone snail, Conus geographus and Conus tulipa, have found that they can also indulge in a different form of chemical warfare, using the blood-sugar-lowering hormone insulin.
Alongside a cocktail of other chemicals, dubbed the nirvana cabal, the snails release the insulin into the surrounding water. Schools of small fish hiding in reef crevices are immobilised as their blood sugar falls rendering them insensible and lacking the metabolic ability to make a sufficiently fast get-away.
The cone snail can then moves in and use its large over-developed mouth to engulf the chemically-stunned fish, which are then dispatched with a different shot of venom and eaten.
Writing in PNAS, Utah University scientist Helena Safavi-Hemami and her colleagues show that, in laboratory tests, the insulin venom reduces the swimming activity of small fish by two thirds.
The chemical structure of the insulin used by the cone snails, which is the smallest active form of insulin yet described, also resembles most closely the fish form of the hormone, maximising its potency.
The researchers suggest that studying it further might also give us clues as to how to make improved insulins for human use.