Spitting cobra

A spitting cobra is any of several species of cobras that can defensively spray a toxic secretion from their fangs. This secretion functions as both a venom (that can be injected via a wound) and a toxungen (that can be sprayed on the target surface).Their ability to spray venom is used for a multiple different things; defensive purposes are the most common instances when a cobra uses it venom.[1] Studies have shown that the target the cobras hit are not random, instead, Spitting cobras intentionally aim and hit the eyes of an aggressor. This article serves as a description of Spitting cobras. It includes background information about the snake, a description of the chemistry of the venom itself, along with the benefits of spitting, and physiological benefits.

Schematic comparison between sections of non-spitting cobra fangs (left) and spitting (right).
Spitting cobras on the right.
1: Section of the whole fang in the sagittal plane.
2: Horizontal section through the fang at the discharge orifice.
3: Frontal view of the discharge orifices.
Juvenile red spitting cobra, Naja pallida
Red spitting cobra

Background
An alert, ready to attack Mandalay spitting cobra (Naja mandalayensis)
Handling of Naja siamensis, using full-face protection

Spitting cobras belong to the Elapid, which comprise species like cobras, mambas, coral snakes, kraits, taipans, death adders and others.[2] Many snakes use their venom as a defensive and predatory mechanism. This includes the Spitting cobra. The Spitting cobra typically inhabits dry savanna and semi-desert environments like the dry, open areas of sub-Saharan region in Africa.[3] It uses its venom primarily as a defense mechanism. The Spitting cobra has the ability to spit venom up to three meters.[1] It primarily does this when it feel threatened or it is being under attack. The trajectory of the venom that the Spitting cobra Spits is not random. The Spitting cobra has evolved to aim the venom that it spits into the antagonists face and eyes.[1] The cobra match the venom distribution to the size of the target when they spit in order to ensure optimal venom distribution.[4]

Venom

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.

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.[5] 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 behavior.[6][7] When cornered, some species "spit" their toxungen as far as 2 m (6.6 ft).[8] While spitting is typically their primary form of defense, all spitting cobras also can deliver their toxin as a venom by biting.

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.[8][9] 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 evolutions roughly correlating with the evolution and/or arrival of early hominins.[10]

Benefits

The ability to spit likely evolved in cobras three times independently through convergent evolution.[11] 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 evolutions roughly correlating with the evolution and/or arrival of early hominins. There are many reasons why an organism undergoes evolution. The Spitting cobra predominantly uses its venom for defensive purposes. It has evolved the ability to spit in order to minimize the risk of contact during an altercation. Even though venomous snakes are very dangerous, they often times are not left injury free after a battle with a predator or larger animal. Being able to spit a toxin from afar dramatically decreases the chances of a Spitting cobra getting injured in a squabble.

The Spitting cobra also has the ability to inject venom through a bite.[12] In fact, a Spitting cobra ejects more venom during a bite than spitting venom. Even though the Spitting cobra has the ability to spray venom at potential threats; spitting is not the way they kill their prey. Just like most snakes in the Elapid clade, Spitting cobras inject their venom through a bite in order to kill their prey. Spitting was evolved as a defense mechanism to deter predators, even if a Spitting cobra blinds a threat, that is not enough to kill the attacker; therefore Spitting cobras can also inject venom directly.

Species

‡: Not a “true spitting cobra”, although these species have the ability to “eject” venom, they rarely do so.

African cobras:

Asian cobras:

Spitting snakes in other families:

Some of the Viperidae have been reported to spit occasionally.[13]

References
  1. Westhoff, G.; Tzschätzsch, K.; Bleckmann, H. (October 2005). "The spitting behavior of two species of spitting cobras". Journal of Comparative Physiology A. 191 (10): 873–881. doi:10.1007/s00359-005-0010-8. ISSN 0340-7594.
  2. Hus, Konrad; Buczkowicz, Justyna; Petrilla, Vladimír; Petrillová, Monika; Łyskowski, Andrzej; Legáth, Jaroslav; Bocian, Aleksandra (2018-03-08). "First Look at the Venom of Naja ashei". Molecules. 23 (3): 609. doi:10.3390/molecules23030609. ISSN 1420-3049. PMC 6017371. PMID 29518026.
  3. Hus, Konrad Kamil; Buczkowicz, Justyna; Petrilla, Vladimír; Petrillová, Monika; Łyskowski, Andrzej; Legáth, Jaroslav; Bocian, Aleksandra (March 2018). "First Look at the Venom of Naja ashei". Molecules. 23 (3): 609. doi:10.3390/molecules23030609. ISSN 1420-3049.
  4. Berthé, Ruben Andres; de Pury, Stéphanie; Bleckmann, Horst; Westhoff, Guido (2009-08-01). "Spitting cobras adjust their venom distribution to target distance". Journal of Comparative Physiology A. 195 (8): 753–757. doi:10.1007/s00359-009-0451-6. ISSN 1432-1351.
  5. Young, B. A.; Dunlap, K.; Koenig, K.; Singer, M. (September 2004). "The buccal buckle: The functional morphology of venom spitting in cobras". Journal of Experimental Biology. 207 (20): 3483–3494. doi:10.1242/jeb.01170. PMID 15339944.
  6. Berthé, Ruben Andres. Spitting behaviour and fang morphology of spitting cobras. Doctoral thesis, Rheinischen Friedrich-Wilhelms-Universität, Bonn, April 2011.
  7. Rasmussen, Sara; Young, B.; Krimm, Heather (September 1995). "On the 'spitting' behaviour in cobras (Serpentes: Elapidae)". Journal of Zoology. 237 (1): 27–35. doi:10.1111/j.1469-7998.1995.tb02743.x.
  8. Panagides, Nadya; Jackson, Timothy N. W.; Ikonomopoulou, Maria P.; Arbuckle, Kevin; Pretzler, Rudolf; Yang, Daryl C.; Ali, Syed A.; Koludarov, Ivan; Dobson, James; Sanker, Brittany; Asselin, Angelique (2017-03-13). "How the Cobra Got Its Flesh-Eating Venom: Cytotoxicity as a Defensive Innovation and Its Co-Evolution with Hooding, Aposematic Marking, and Spitting". Toxins. 9 (3): E103. doi:10.3390/toxins9030103. ISSN 2072-6651. PMC 5371858. PMID 28335411.
  9. Leslie, Mitch (2021-01-21). "Spitting cobras' venom evolved to inflict pain". Science. doi:10.1126/science.abg6859. ISSN 0036-8075. S2CID 234134648.
  10. Kazandjian, T. D.; Petras, D.; Robinson, S. D.; van Thiel, J.; Greene, H. W.; Arbuckle, K.; Barlow, A.; Carter, D. A.; Wouters, R. M.; Whiteley, G.; Wagstaff, S. C.; Arias, A. S.; Albulescu, L.-O.; Plettenberg Laing, A.; Hall, C.; Heap, A.; Penrhyn-Lowe, S.; McCabe, C. V.; Ainsworth, S.; da Silva, R. R.; Dorrestein, P. C.; Richardson, M. K.; Gutiérrez, J. M.; Calvete, J. J.; Harrison, R. A.; Vetter, I.; Undheim, E. A. B.; Wüster, W.; Casewell, N. R. (2021). "Convergent evolution of pain-inducing defensive venom components in spitting cobras" (PDF). Science. 371 (6527): 386–390. Bibcode:2021Sci...371..386K. doi:10.1126/science.abb9303. ISSN 0036-8075. PMC 7610493. PMID 33479150.
  11. Wüster, Wolfgang; Crookes, Steven; Ineich, Ivan; Mané, Youssouph; Pook, Catharine E.; Trape, Jean-François; Broadley, Donald G. (2007-11-01). "The phylogeny of cobras inferred from mitochondrial DNA sequences: Evolution of venom spitting and the phylogeography of the African spitting cobras (Serpentes: Elapidae: Naja nigricollis complex)". Molecular Phylogenetics and Evolution. 45 (2): 437–453. doi:10.1016/j.ympev.2007.07.021. ISSN 1055-7903.
  12. Hayes, William K.; Herbert, Shelton S.; Harrison, James R.; Wiley, Kristen L. (September 2008). "Spitting versus Biting: Differential Venom Gland Contraction Regulates Venom Expenditure in the Black-Necked Spitting Cobra, Naja nigricollis nigricollis". Journal of Herpetology. 42 (3): 453–460. doi:10.1670/07-076.1. ISSN 0022-1511.
  13. Wüster, Wolfgang; Thorpe, Roger S. (December 1992). "Dentitional phenomena in cobras revisited: Spitting and fang structure in the Asiatic species of Naja (Serpentes: Elapidae)" (PDF). Herpetologica. 48 (4): 424–434. JSTOR 3892862.
  • Greene, Harry W. (1997) Snakes: The Evolution of Mystery in Nature. University of California Press, Berkeley and Los Angeles, California.
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