Editing Snakebite (section)

== Mechanics ==
{{see also|Envenomation}}
[[File:Snake Venom Delivery System Diagram.jpg|thumb|Basic diagram of a snake's venom delivery system]]
When venomous snakes bite a target, they secrete [[venom]] through their venom delivery system. The venom delivery system generally consists of two venom glands, a compressor muscle, venom ducts, a fang sheath, and [[fang]]s. The primary and accessory venom glands store the venom quantities required during [[envenomation]]. The compressor muscle contracts during bites to increase the pressure throughout the venom delivery system. The pressurized venom travels through the primary venom duct to the secondary venom duct that leads down through the fang sheath and fang. The venom is then expelled through the exit [[Body orifice|orifice]] of the fang. The total volume and flow rate of venom administered into a target varies widely, sometimes as much as an order of magnitude. One of the largest factors is snake species and size, larger snakes have been shown to administer larger quantities of venom.<ref name="Hayes et al. 2002"/>

=== Predatory vs. defensive bites ===
Snake bites are classified as either predatory or defensive. During defensive strikes, the rate of venom expulsion and total volume of venom expelled is much greater than during predatory strikes. Defensive strikes can have 10 times as much venom volume expelled at 8.5 times the flow rate.<ref>{{cite journal | vauthors = Young BA, Zahn K | title = Venom flow in rattlesnakes: mechanics and metering | journal = The Journal of Experimental Biology | volume = 204 | issue = Pt 24 | pages = 4345–4351 | date = December 2001 | pmid = 11815658 | doi = 10.1242/jeb.204.24.4345| bibcode = 2001JExpB.204.4345Y }}</ref> This can be explained by the snake's need to quickly subdue a threat. While employing similar venom expulsion mechanics, predatory strikes are quite different from defensive strikes. Snakes usually release the prey shortly after the envenomation allowing the prey to run away and die. Releasing prey prevents retaliatory damage to the snake. The venom scent allows the snake to relocate the prey once it is deceased.<ref name="Hayes et al. 2002">{{cite book |chapter=Factors that influence venom expenditure in viperids and other snake species during predatory and defensive contexts | vauthors = Hayes WK, Herbert SS, Rehling GC, Gennaro JF |year=2002 |url= http://eaglemountainpublishing.s3.amazonaws.com/PDF/Biology%20of%20the%20Vipers/CH%2013_hayes_.pdf |title=Biology of the Vipers |pages=207–233 |publisher=Eagle Mountain Publishing}}</ref> The amount of venom injected has been shown to increase with the mass of the prey animal.<ref>{{cite journal | vauthors = Hayes WK |title=Venom metering by juvenile prairie rattlesnakes, ''Crotalus v. viridis'': effects of prey size and experience |journal=Animal Behaviour |date=1995 |volume=50 |issue=1 |pages=33–40 |doi=10.1006/anbe.1995.0218|s2cid=53160144}}</ref> Larger venom volumes allow snakes to effectively euthanize larger prey while remaining economical during strikes against smaller prey. This is an important skill as venom is a metabolically expensive resource.{{citation needed|date=May 2021}}

=== Venom metering ===
Venom metering is the ability of a snake to have neurological control over the amount of venom released into a target during a strike based on situational cues. This ability would prove useful as venom is a limited resource, larger animals are less susceptible to the effects of venom, and various situations require different levels of force. There is a lot of evidence to support the venom metering hypothesis. For example, snakes frequently use more venom during defensive strikes, administer more venom to larger prey, and are capable of dry biting. A dry bite is a bite from a venomous snake that results in very little or no venom expulsion, leaving the target asymptomatic.<ref>{{cite journal | vauthors = Naik BS | title = "Dry bite" in venomous snakes: A review | journal = Toxicon | volume = 133 | pages = 63–67 | date = July 2017 | pmid = 28456535 | doi = 10.1016/j.toxicon.2017.04.015 | bibcode = 2017Txcn..133...63N | s2cid = 36838996}}</ref> However, there is debate among many academics about venom metering in snakes. The alternative to venom metering is the pressure balance hypothesis.{{citation needed|date=March 2023}}

The pressure balance hypothesis cites the retraction of the fang sheath as the many mechanisms for producing outward venom flow from the venom delivery system. When isolated, fang sheath retraction has experimentally been shown to induce very high pressures in the venom delivery system.<ref>{{cite journal | vauthors = Young BA, Kardong KV | title = Mechanisms controlling venom expulsion in the western diamondback rattlesnake, Crotalus atrox | journal = Journal of Experimental Zoology Part A: Ecological Genetics and Physiology | volume = 307 | issue = 1 | pages = 18–27 | date = January 2007 | pmid = 17094108 | doi = 10.1002/jez.a.341 | doi-access = free | bibcode = 2007JEZA..307...18Y}}</ref> A similar method was used to stimulate the compressor musculature, the main muscle responsible for the contraction and squeezing of the venom gland, and then measuring the induced pressures. It was determined that the pressure created from the fang sheath retraction was at times an order of magnitude greater than those created by the compressor musculature. Snakes do not have direct neurological control of the fang sheath, it can only be retracted as the fangs enter a target and the target's skin and body provide substantial resistance to retract the sheath. For these reasons, the pressure balance hypothesis concludes that external factors, mainly the bite and physical mechanics, are responsible for the quantity of venom expelled.{{citation needed|date=March 2023}}

=== Venom spitting ===
Venom spitting is another venom delivery method that is unique to some Asiatic and African [[cobra]]s. In venom spitting, a stream of venom is propelled at very high pressures outwards up to 3 meters (300 centimeters). The venom stream is usually aimed at the eyes and face of the target as a deterrent for predators. There are non-spitting cobras that provide useful information on the unique mechanics behind venom spitting. Unlike the elongated oval shaped exit orifices of non-spitting cobras, spitting cobras have circular exit orifice at their fang tips.<ref>{{cite journal | vauthors = Bar-On B | title = On the form and bio-mechanics of venom-injection elements | journal = Acta Biomaterialia | volume = 85 | pages = 263–271 | date = February 2019 | pmid = 30583109 | doi = 10.1016/j.actbio.2018.12.030 | s2cid = 58587928}}</ref> This combined with the ability to partially retract their fang sheath by displacing the palato-maxillary arch and contracting the adductor mandibulae, allows the spitting cobras to create large pressures within the venom delivery system.<ref>{{cite journal | vauthors = Young BA, Dunlap K, Koenig K, Singer M | title = The buccal buckle: the functional morphology of venom spitting in cobras | journal = The Journal of Experimental Biology | volume = 207 | issue = Pt 20 | pages = 3483–3494 | date = September 2004 | pmid = 15339944 | doi = 10.1242/jeb.01170 | doi-access = free| bibcode = 2004JExpB.207.3483Y }}</ref> While venom spitting is a less common venom delivery system, the venom can still cause the effects if ingested.{{citation needed|date=May 2021}}