my-server
← Wiki

Coral snake

Coral snakes are a large group of elapid snakes that can be divided into two distinct groups, the Old World coral snakes and New World coral snakes. There are 27 species of Old World coral snakes, in three genera (Calliophis, Hemibungarus, and Sinomicrurus), and 83 recognized species of New World coral snakes, in two genera (Micruroides and Micrurus). Phylogenetic studies suggest that the group originated in the Old World. While new world species of both genera are venomous, their bites are seldom lethal; as of 2018, only two confirmed fatalities had been documented in the United States in the preceding 100 years from the genus Micrurus. Meanwhile, snakes of the genus Micruroides have never caused a medically significant bite.

North American coloration patterns

Experts now recognize that certain coloration patterns and common mnemonics—such as the phrase “Red against yellow, deadly fellow; red against black, friendly Jack,” which people sometimes use to distinguish between the venomous coral snake and the non-venomous milksnake—are not consistent enough to be trustworthy. While any snake exhibiting the coral snake's colors and banding pattern in the southeastern United States will almost certainly be a coral snake, there are coral snakes in other parts of the world that are colored differently.

Coral snakes in the United States are most notable for their red, yellow/white, and black-colored banding. However, several nonvenomous species in the U.S. have similar (though not identical) bandings, including the two scarlet snake species in the genus Cemophora, and some of the kingsnakes (including the aforementioned milksnakes) in the genus Lampropeltis. However, in reference to the mnemonic phrase “red touching yellow, a deadly fellow,” some of these kingsnakes do not naturally display any red touching yellow. Additionally, some ground snakes in the genus Sonora (of the southwestern U.S.) can have a color pattern that matches that of the sympatric Sonoran coral snake (Micruroides euryxanthus). No genuine coral snake in the U.S. exhibits red bands of color in contact with bands of black, except in rare cases of an aberrant pattern. Thus, while on extremely rare occasions when a certain non-venomous snake might be mistaken for a coral snake, the mnemonic holds true. However, a red–yellow–black banded snake in the U.S. (whose red and black banding actually touch) is rarely a venomous coral snake.

Furthermore, the mnemonic is not consistently accurate for North American coral snake species found south of the U.S. Some species, like Mexico’s Oaxacan coral snake (Micrurus ephippifer) or Clark's coral snake (Micrurus clarki, of Costa Rica & Panama), do actually fit the mnemonic; others, like the Honduran Roatan coral snake (Micrurus ruatanus), or the redtail coral snake (Micrurus mipartitus) of Panama, do not. Some South American coral snakes will fit the mnemonic, while others do not. The South American tricolored hognose snake (Xenodon pulcher) has repeated bands of red-black-white-black, imitating the coral snake as a defense mechanism, with the key visual difference being their upturned snout (used for burrowing). The hognoses are, actually, mildly rear-fanged venomous; although generally not considered serious to humans, anecdotal research has suggested the South American hognoses to possess slightly more potent venom than the North American hognoses. In the Old World, none of the coral snake species usually fit the mnemonic.

Most species of coral snake are small in size. North American species average around in length, but specimens of up to or slightly larger have been reported. Some coral snakes live in the water but most of them do not. Aquatic species have flattened tails that act as fins, aiding in swimming.

Behavior

Coral snakes vary widely in their behavior, but most are very elusive, fossorial (burrowing) snakes which spend most of their time buried beneath the ground or in the leaf litter of a rainforest floor, coming to the surface only when it rains or during breeding season. Some species, like Micrurus surinamensis, are almost entirely aquatic and spend most of their lives in slow-moving bodies of water that have dense vegetation.

Coral snakes feed mostly on smaller snakes, lizards, frogs, nestling birds, small rodents, etc. Tropical species of coral snakes from more mesic areas have a broader diet, feeding on elongate prey like eels and caecilians.

Like all elapid snakes, coral snakes possess a pair of small hollow fangs to deliver their venom. The fangs are positioned at the front of the mouth. The fangs are fixed in position rather than retractable, and rather than being directly connected to the venom duct, they have a small groove through which the venom enters the base of the fangs. Because the fangs are relatively small and inefficient for venom delivery, rather than biting quickly and letting go (like vipers), coral snakes tend to hold onto their prey and make chewing motions when biting. The venom takes time to reach full effect. It is a neurotoxin, affecting the nervous system and weakening the muscles.

Coral snakes are not aggressive or prone to biting and account for less than one percent of the total number of snake bites each year in the United States. The life span of coral snakes in captivity is about seven years.

Reproduction

M. fulvius reproduction is internal fertilization through the use of hemipenes. The breeding season occurs from spring to early summer and late summer to early fall. Male combat is not typical in M. fulvius as males are smaller than females. Micrurus fulvius are oviparous and typically lay eggs from May to July. During early spring females will undergo sudden vitellogenesis–oocyte and yolk formation–in preparation for breeding. Approximately 37 days post fertilization oviposition occurs and the average clutch size ranges from five to seven eggs. However, some in captivity have laid as many as thirteen eggs. The incubation period of the M. fulvius eggs normally reaches 60 days. Males also undergo sexual changes throughout the year, testicular recrudescence start in the fall and testicular regression occurs come spring. However, males typically have mature sperm residing in the epididymis year round and are capable of storing sperm in the deferent duct over the winter till the females are receptive. A study investigating how climate influences the reproductive cycle discovered species found closer to the equator displayed more continuous cycles while those in colder regions had more seasonal cycles. With increasing temperatures as a result of climate change, continuous cycles have the possibility of becoming more prevalent. Offspring reach maturation depending on sex, males mature at roughly 11 to 16 months while females reach maturity later at 26 months.

Distribution (U.S.)

New World coral snakes exist in the southern range of many temperate U.S. states. Coral snakes are found in scattered localities in the southern coastal plains from North Carolina to Louisiana, including all of Florida. They can be found in pine and scrub oak sandhill habitats in parts of this range, but sometimes inhabit hardwood areas and pine flatwoods that undergo seasonal flooding.

There is controversy about the classification of the very similar Texas coral snake as a separate species. Its habitat, in Texas, Louisiana, and Arkansas is separated from the eastern coral snake's habitat by the Mississippi River. The coral snake population is most dense in the southeastern United States.

The Arizona coral snake is classified as a separate species and genus and is found in central and southern Arizona, extreme southwestern New Mexico and southward to Sinaloa in western Mexico. It occupies arid and semiarid regions in many different habitat types, including thornscrub, desert-scrub, woodland, grassland and farmland. It is found in the plains and lower mountain slopes, at elevations ranging from sea level to ; often found in rocky areas.

Danger to humans

New World coral snakes possess one of the most potent venoms of any North American snake. However, relatively few bites are recorded due to their reclusive nature and the fact they generally inhabit sparsely populated areas. Even in areas that are densely populated, bites are rare. According to the American National Institutes of Health, there are an average of 15–25 coral snake bites in the United States each year. When confronted by humans, coral snakes will almost always attempt to flee, and bite only if restrained. In addition, coral snakes have short fangs (proteroglyph dentition) that cannot penetrate thick clothing although bites are possible through normal thin clothing. Any skin penetration, however, is a medical emergency that requires immediate attention.

Historically, the venom of the North American Micrurus and Micruroides species was believed to contain powerful neurotoxins which could paralyze the breathing muscles, requiring mechanical or artificial respiration. It was usually reported that there was only mild pain associated with a bite and that respiratory failure could occur and onset of clinical symptoms may be delayed for as much as 10 to 18 hours. Coral snake venom contains a neurotoxic component and symptoms include pain from the bite, sialorrhea, paresthesia, ptosis, weakness, blurred vision, paralysis, fasciculation and diplopia. However recent studies on the bites of the Texas coral snake (Micrurus tener) have shown that these bites rarely require antivenom, don't usually show any systemic respiratory problems and can be intensely painful. Further studies are necessary to see if these clinical features are true of all Micrurus species. Body length in coral snakes appears to be positively associated with venom yield.

Shortages of coral snake antivenom were previously reported, but one source states that production has resumed and, Pfizer indicates that antivenom is available.

Old World

Genus Calliophis

Species in this genus are:

Nota bene: A binomial authority in parentheses indicates that the species was originally described in a genus other than Calliophis.

Genus Hemibungarus

Species in this genus are:

Genus Sinomicrurus

Species in this genus are:

New World

Genus Micruroides

Genus Micrurus

Nota bene: In the following list, a binomial authority or a trinomial authority in parentheses indicates that the species or subspecies was originally described in a genus other than Micrurus.

Mimicry

New World coral snakes serve as models for their Batesian mimics, false coral snakes, snake species whose venom is less toxic, as well as for many nonvenomous snake species that bear superficial resemblances to them. The role of coral snakes as models for Batesian mimics is supported by research showing that coral snake color patterns deter predators from attacking snake-shaped prey, and that in the absence of coral snakes, species hypothesized to mimic them are indeed attacked more frequently. Species that appear similar to coral snakes include:

References

Further reading

  • Boulenger, G.A. (1896). Catalogue of the Snakes in the British Museum (Natural History). Volume III., Containing the Colubridæ (Opisthoglyphæ and Proteroglyphæ)…. Trustees of the British Museum (Natural History). (Taylor and Francis, Printers.) London. xiv + 727 pp. + Plates I.- XXV. (Elaps, 28 species, pp. 411–433 + Plate XX.)
  • Roze, J.A. (1996). Coral Snakes of the Americas: Biology, Identification, and Venoms. Krieger. Malabar, Florida. 340 pp. .
  • Tanaka, G.D.; Furtado MD, F.D.; Portaro, F.C.V.; Sant'Anna, O.A.; Tambourgi, D.V. (2010). "Diversity of Micrurus Snake Species Related to Their Venom Toxic Effects and the Prospective of Antivenom Neutralization". PLoS Neglected Tropical Diseases 4(3): e622.
  • Universidad de Costa Rica (2009). El envenenamiento por mordedura de serpiente en Centroamérica ("Snakebite poisonings in Central America"). San José, Costa Rica: Instituto Clodomiro Picado, Facultad de Microbiología, Universidad de Costa Rica.