Cobras are renowned for their devastating flesh-eating venom, and the dramatic way they rear their heads upwards to flare their hoods. New research clarifies the purpose of these tactics and how they emerged among cobras—insights that could help scientists develop more powerful anti-venoms, and help you spot an especially deadly cobra before it’s too late.
A new study published in the science journal Toxins explores how cobras developed their potent venoms, which are used for both predation and defense, and how the strength of this deadly substance can be linked to their dramatic hooding behavior and striking visual appearance. In addition to shedding light on cobra evolution and behavior, these findings could lead to improved anti-venoms, and possibly new medicines to treat cancer.
There are over 270 cobra species spread throughout Africa and Asia, and they exact a terrible toll on their animal and human victims. Their venom, which is delivered by either biting or spitting, can cause extreme pain, blindness, respiratory failure, possible amputation of limbs, and even death. But while the potency of cobra venom is well known, the evolutionary story behind the cobra’s unique weapon has remained a mystery. Scientists aren’t entirely sure if the venom—a flesh-devouring “cytotoxin”— serves a defensive purpose, or if it evolved for prey capture. The new research, led by Bryan Fry from the University of Queensland, attempts to answer these questions.
For the study, Fry’s team analyzed the venoms of nearly 30 cobra species and related snakes, while also performing a genetic analysis on each snake. The researchers found that flesh-eating venom evolved in tandem with the cobra’s distinctive hoods; as the venom got stronger over time, the displays got more elaborate. What’s more, the more toxic the venom, the more inclined the cobra is to rear upwards and flare its hood. As it evolved, cobra venom became increasingly potent in parallel to its other warning strategies, such its ornate hood markings, body bandings, red coloring, and spitting. Eventually, the potency of the venom, plus the rearing behavior, led to the rise of spitting cobras.
“Their spectacular hoods and eye-catching patterns evolved to warn off potential predators because unlike other snakes, which use their venom purely for predation, cobras also use it in defence,” said Fry in a statement. “For the longest time it was thought that only spitting cobras had these defensive toxins in high amounts in their venoms, however we’ve shown that they are widespread in cobras.”
The potency of a cobra’s venom evolved primarily as a defence mechanism, and it emerged twice alongside hooding behavior—once in the ring-necked spitting cobra and “true” cobras, and again, independently, in king cobras.
As this research suggests, these traits evolved hand-in-hand—the venom acting as the bona fide defensive measure, and the hooding behavior and markings serving as warning. Without deadly venom to back it all up, the cobra’s gestures would stand for nothing against its natural predators, such as mongooses and large birds of prey. Yes, its venom is deadly, but a cobra stands a better chance of surviving an encounter if its enemy simply backs off.
As noted, the researchers say spitting behavior emerged among an offshoot of cobras as a result of the venom’s toxicity, and as a result of the hooding behavior. Spitting evolved three times within cobras, in the ring-necked spitting cobra and also in both the African and Asian “true” cobras. Meanwhile, the water cobra, Naja annulata, lost its hooding abilities and its flesh-destroying venom when it adapted to the water, but it developed a different kind of weapon—a neurotoxic venom, similar to those of other aquatic sea snakes.