Geography Cone Snail

A Pretty Shell With a Harpoon Inside

The Geography Cone Snail (Conus geographus) wears a smooth shell with small bumps at the shoulder, mottled brown or red over white, cream or rose pink. It measures 70 to 150 millimeters and weighs between 13.3 and 62 grams, with an average of 38.8 grams. It lives on living or broken coral reefs and in sandy tidal zones across the tropical and subtropical Indo-Pacific, including the northern shores of Australia. It is found mostly just below the tideline, with a recorded depth range of 0 to 200 meters. By day it lies buried in the sand; at night it hunts.

The Nirvana Cabal Conus geographus is believed to prey on fish hiding in reef crevices at night. Its venom insulin appears to be part of a toxin mix researchers call the nirvana cabal, released into the water to disorient schools of small fish.

Fishing With a Sugar Crash

Researchers found specialized insulins as major components in the venoms of two fish-hunting cone snails, Conus geographus and the tulip cone (Conus tulipa). Injected into fish, the venom insulin causes hypoglycemic shock, a dangerous drop in blood sugar. Its discoverers say their evidence suggests it is “specifically used as a weapon for prey capture” by cone snails that hunt with a net strategy: disoriented fish are easier to engulf with the snail’s distended false mouth, which works like a net.

It also uses the hook-and-line method: it slowly approaches its prey, waving its proboscis like a lure to attract the fish before stinging it with its radula. The fish jerks violently for a few moments and is hit with a paralyzing venom that stiffens it, and the snail swallows its catch whole, regurgitating the bones hours or days later. Either way, the venom goes in through a hollow radular tooth used as a harpoon.

Gene-sequencing work on its venom duct found that the most highly expressed toxin is not paralytic: it “causes sensory disorientation.” The team’s data suggest that disorienting prey is central to how the snail uses its venom.

The Deadliest Shell on the Reef

The same team calls Conus geographus “the deadliest snail on earth,” the cone snail behind most of the human fatalities recorded in the medical literature. Citing earlier work, their paper states that in the absence of medical intervention, 70% of human stinging cases are fatal. Another team found an apparent link between the amount of venom a snail injects and the size of its shell, and used it to extrapolate a human lethal dose of 0.029 to 0.038 milligrams per kilogram of body weight from one historic fatal case.

The venom insulin also interests diabetes researchers. A later study found that venom insulins from Conus geographus, the tulip cone and a third species, Conus kinoshitai, differ in sequence, yet all bind to and activate the human insulin receptor. Tested in zebrafish and mice, venom insulins significantly lowered blood glucose in a lab model of diabetes, which the authors say offers insight into designing new diabetes drugs.