Spitting cobra

Venomous snakes use venom as both a defensive and predatory mechanism, which includes the spitting cobras. Spitting cobras belong to the Elapidae, which comprises the cobras, mambas, coral snakes, kraits, taipans, death adders, and sea snakes.^[4]

Spitting cobras typically inhabit dry savanna and semi-arid environments, particularly the hotter, open areas of sub-Saharan Africa.^[4] They use venom primarily as a means of defense: spitting cobras have the ability to project venom several metres away from its location, and to accurately target the face of a potential threat.^[1] The cobras can measure and adjust the venom dosage being delivered, based on the size and relative distance of their target, in order to ensure the highest envenomation potential possible.^[5]

A 2021 study showed that the evolution of spitting in three cobra lineages, which are Hemachatus along with some African and Asian Naja species, corresponds to the separation of the human and chimpanzee evolutionary lineages in Africa and the arrival of Homo erectus in Asia. The authors therefore hypothesize that the arrival of bipedal, tool-using primates may have triggered the evolution of spitting in cobras.^[6]

Most spitting cobras' venom/toxungen is significantly cytotoxic, apart from the neurotoxic and cardiotoxic effects typical of other cobra species. The ability to spit likely evolved in cobras three times independently through convergent evolution.^[7][8] In each of these three events, the venom convergently evolved to be more effective at creating pain in mammals to serve as a better deterrent, with each of the three origins roughly correlating with the evolution and/or arrival of early hominins.^[6]

The toxungen sprays out in distinctive geometric patterns when muscles squeeze the glands to squirt it out through forward-facing holes near the tips of the fangs.^[9] Individuals of some species of spitting cobras make hissing exhalations/lunging movements of their heads when "spitting", and such actions may assist in propelling the venom, but research does not support the hypothesis that they play any major functional part except possibly enhancing the threatening effect of the behaviour.^[10][11] When cornered, some species "spit" their toxungen as far as 2 m (6.6 ft).^[7]

The spat toxungen is generally harmless on intact mammalian skin (although contact can result in delayed blistering of the area), but can cause permanent blindness if introduced to the eye; if left untreated it may cause chemosis and corneal swelling. Spitting cobras evolved higher pain-inducing venom through increased phospholipase A2 levels, which potentiate the pain-inducing action of the cytotoxins present in most cobra venoms.^[6]

While spitting is typically their primary form of defense, all spitting cobras are still able to envenomate by biting. Bites are their primary method of killing prey, and delivers more venom than spitting, which is a purely antipredatory behavior.^[12]

African cobras:

Asian cobras:

The following cladogram follows the analysis of Lee (2016), with the spitting taxa bolded:^[7]

Additionally, some of the Viperidae have been reported to spit occasionally.^{[example needed][13]}