Our group prepares to leave Lighthouse Cave, San Salvador, Bahamas.
Costa Rica has a diverse landscape, which leads to a large amount of species richness and diversity. Costa RicaÕs rainforest aides in its species richness, but the coast, mountains, and dry tropical forests encourage an even larger selection. Venomous snakes are no exception, with 3 separate families, 8 genera and 17 species found there. While there are 127 known species of snakes in Costa Rica, venomous snakes still have a large impact on the ecosystem. Venomous snakes are important predators in many different ecosystems in Costa Rica. They have intriguing lifestyles, physiology, and behavior.
Snakes are unique in that as they evolved they lost their limbs. These animals have adapted by altering their internal organization and senses. Snakes have an extended body. They have more vertebrae than any other vertebrate. Their vertebrae are connected by a ball and socket joint, which allows for more movement and a stronger connection. Snakes swallow their food whole, which complicates the processes in the body even more. In order to get the food down, their mandibles are separate so that the food fits into their body. There muscles are designed for movement and using an undulating motion allows them to move their food down their esophagus. They also have ribs that donÕt connect ventrally. This allows their bodies to expand when they eat. Snakes esophagus and stomachs are the same and their small intestines are the only organ that is wrapped up and twisted. Every other organ is straight so that the body can remain slender. Their lungs are very thin, with the right lung being larger and longer than the left. The kidneys and gonads are paired so that one of the pair is shifted down. Snakes have a single cloaca, where the digestive, urinary, and reproductive tract empties. In order to retain the correct amount of water snakes excrete uric acid instead of urine similar to birds. The reproductive system is altered to fit into a snakeÕs bodies. The reproductive organ of males is the hemipene. Each male has two that are connected.
Reproduction in snakes varies quite a bit from species to species. Snakes are usually solitary creatures. Mating season is when most snakes interact with other individuals in their species. Males begin to fight for mates. The battles between males are usually not violent. They look similar to copulation. The males intertwine their bodies, they continue until one of the snakes give up. When snakes copulate the male intertwines its tail with the females and lifts the females tail so that their cloacas match up. Snakes, along with reproduction, have several different types of offspring care. Many species are oviparous. They lay eggs and leave them. Certain species that lay eggs stay near the eggs for several days to protect them. Other snakes have adapted to carrying the eggs inside them and giving birth. This is called ovoviviparous. There are even some species that are viviparous and give birth to live young.
The senses of snakes have been adapted to their lifestyles and structure. Most snakes have bad eyesight. The blind snakes can only tell the difference between light and dark. Most snakesÕ eyesight is just to detect movement. There are certain snakes that do have very good eyesight. These snakes are usually diurnal species. Snakes hearing is not a well-developed sense either. Snakes have no external ear and feel vibrations through their mandible. They can hear low vibrations from the substrate. They have a great sense of touch. Snakes skin is very sensitive. Smell is the best sense that the snake has. Snakes use their tongue to gather odor molecules in the air and these are analyzed by the JacobsonÕs organ. This organ is on the roof of the mouth and is brushed over by the tongue every time it is pulled back into the snakeÕs mouth. Some snakes have an additionally sense. Some snakes such as pitvipers and boas have thermal pits. These pits detect heat and can be used to find food. These pits nerves are crossed with the occipital nerves, which allow snakes to almost see by heat.
Snakes have found many ways in defending themselves from predators. The cloaca has a special scent gland that releases a smell, which can be used for protection when a snake is threatened. Aside from their scent glands, they can also be protected by their coloration. In many species coloration changes over time. There are different types of coloration, all of which are designed to help the snakes avoid predators and capture prey. They could have cryptic coloration. This allows them to blend in with their surroundings. This is true with many arboreal snakes that have a green pigment. Snakes can have a disruptive coloration, with complicated patterns. This blurs their figure and allows them to move without being definable. The final coloration is aposematic. This kind of coloration is a warning to other animals. The snakes with this coloration are venomous or copying a venomous species. They are brightly colored.
A trait that some snakes share that can help protect them and help them capture prey is venom. Snakes that have hallow fangs and special DuvernoyÕs gland produce and secrete venom. Venom is speculated to have first been used to aid in ingestion and digestion. There are many different kinds of venom. There are neurotoxins, coagulants, haemorrhagins, haemotoxins, myotoxins, cytotoxins, nephrotoxins, and sarafotoxins. Neurotoxins affect the synapse between nerves and muscles causing paralysis. Coagulants affect how the blood clots. Venomous snakes can either have procoagulants, which clot blood more readily or anticoagulants, which inhibit clotting of the blood. Haemorrhagins and haemotoxins weaken blood vessel walls, which then break very easily. Myotoxins damage muscle. This can cause death if it affects the respiratory muscle. Cytotoxins break down tissue and cause necrosis. Nephrotoxins damage the kidneys and cause renal failure. Sarafotoxins narrow blood vessels. No Costa Rican snake has either sarafotoxins or nephrotoxins. The venomous snakes of Costa Rica all have prominent anterior fangs. There are some species of colubrid or harmless snakes that have a small amount of venom, but have posterior teeth so that it is almost impossible to invenomation by striking. There are also species that arenÕt considered venomous, but their saliva irritates the area that has been bitten.
The three families of venomous snakes in Costa Rica are Hydrophidae, Elapidae, and Viperidae. The eight genera of venomous snakes are Pelamis, Micrurus, Agkistroden, Bothriechis, Bothrops, Crotalus, Lachesis, and Porthidium. There is only one species from the Hydrophidae family that resides in Costa Rica. The species Pelamis platuyus are sea snakes. They live off of the coast of the Pacific coast in Coast Rica. They have one of the largest ranges of all sea snakes. They range from India, Africa, and Australia to the coast of California to the coast of Ecuador. During the dry season in Costa Rica there is a huge gathering of commonly called yellow-bellied sea snake or pelagic sea snake. They gather in shallow waters, where sea currents run into each other, or where rivers end and at bay mouths. Pelagic sea snakes feed on small fish and are able to strike side ways and swim backwards with great agility. These snakes are at the top of their food chain and have no common predators. Fish, sharks, and birds avoid them. Sea snakes have evolved to be able to live permanently in salt water. Pelagic sea snakes have a flattened head and a vertically flattened tail, which allows it to swim. They have special valved nostrils. Yellow-bellied sea snakes are able to hold their breath for three hours. They are so specialized for salt water that they are unable to move successfully on land. They spend much of their time at the surface of the water because they are ectoderms like all other snakes and need to be warmed by the sun. They also mate on the surface. They also have adapted to living in water by giving to live birth. There are usually less offspring, but they are larger. Although these are highly venomous animals they are usually very calm and rarely bite humans. There have been known casualties and if one was bitten by one they would need attention immediately. They have both postsynaptic neurotoxins and myotoxins that are secreted from an anterior fang and a bit can be fatal.
The second family is Elapidae. These are coral snakes. While there are three genera of coral snakes there is only one in Costa Rica, Micrurus. There are four species of coral snakes in Costa Rica: Micrurus alleni, Micrurus multifasciatus, Micrurus clarki, and Micrurus nigrocinctus. All coral snakes have certain similarities. They have a thin head and body with small black eyes. They are either bi-colored or tri-colored. They are banded with black, white or yellow, and red. If they are bi-colored they unusually are black and yellow. There are many variations on the colors of coral snakes. There are species that have orange rings instead of yellow or pink instead of red. Black is always present. There are different patterns, which are defined by the number of black band. This can result in either a black band between two yellow bands, then red bands or black-yellow-black-yellow-black then red. These animals are very secretive and tend to be nocturnal and burrow during the day in debris. They are responsible for 0.9% of all serious bites in Latin America. This is because of their secretive nature and there small fangs. While they account for very little of the fatalities from snakes they do have very potent venom. They are relatives of cobras and have powerful neurotoxins, which affect the postsynaptic channels of the efferent nerves. This leads to paralysis and respiratory arrest. The venom begins to affect the victim in 2 hour and takes full effect by 48 hours. The anti-venom is widely available and if one is bite it should be administered immediately. All species of coral snakes have this venom, but they each have different behaviors and habitats.
The species in Costa Rica show how these species are so different. M. alleni or AllenÕs coral snakes lives near water. There are populations in rainforests on both the Atlantic and Pacific coasts of Costa Rica. The only difference between these is that the Pacific population tends to have yellow bands and the Atlantic population has white bands. Both of these populations eat eels, lizards, and smaller snakes. These species have the traditional red-yellow-black-yellow-red pattern, but black specks appear on the red bands. Micrurus clarki, also known as ClarkÕs coral snake resides in southeast Costa Rica. This species is tri-colored, but it is easy to tell the difference between ClarkÕs coral snake and AllenÕs coral snake. M. clarki usually has orange bands instead of yellow and the red bands are almost pinkish. They also have 13-20 black bands, where M. alleni has 26 black bands. This species live mostly in rainforests and eat other snakes. There are many snakes that share similar coloration, but are harmless. Micrurus nigrocinctus can be found almost anywhere in Costa Rica. It lives in rainforests and dry forests. M. nigrocinctus is also called Central American coral snake and spreads throughout all of Middle America. They are tri-colored making it difficult to tell the difference between M. alleni and M. nigrocinctus. The only differenced is the number of black bands and that occasionally in M. nigrocinctus the yellow bands are thin or covered by black pigment. If the species does have yellow bands then one could count the black bands. M. alleni has 26 bands and M. nigrocinctus has 10-25 bands. The final species of coral snakes that resides in Costa Rica is the multi-banded coral snake, Micrurus multifasciatus. This snake resides in northwest Costa Rica. They usually live in rainforests, but occasionally can be found in dry forests. They are the only bi-colored species in Costa Rica. The multi-banded coral snake has alternating bands of black, red, white, or yellow. There have been a few of this species that are completely black and white, but usually they have red or black and yellow or white bands. These species are active during the early morning and late afternoon. They are nervous snakes and bite if threatened.
The final family in Costa Rica is Viperidae. This family makes up the majority of venomous snakes in Costa Rica, with 6 different genera and 12 species. Vipers can be arboreal or terrestrial. They have triangular heads and their striking position is an S shape. All vipers have two anterior fangs attached to their maxillaries. Vipers have powerful venom that is usually a neurotoxin. All vipers are viviparous, which means they give birth to live young. The American vipers are called pitviper because they all have infrared sensing pits behind there nostrils. These pits allow them to find prey easily. These pits can detect temperatures as different as 1 degree and can detect heat from over a yard. Many species in this group are known to rattle their tails against leaves and plants to warn predators. There are a few arboreal species that donÕt do this. The species of pitvipers in Costa Rica are Agkistroden bilineatus, Bothriechis lateralis, B. nigroviridis, B. schlegelii, Bothrops asper, Crotalus durissus, Lachesis melanocephala, Porthidium godmani, P. nasutum, P. nummifer, P. ophryomegas, and P. picadoi.
The genus Agkistroden only includes two species; copperheads and Cantil. Copperheads live in North America and Cantils reside in Latin America. Cantil means Òviper-snakeÓ in Mayan. Agkistroden bilineatus lives on the Pacific coast of Costa Rica in tropical dry forests. Cantils are the more venomous of the two species. Its venom has procoagulants, myotoxins, and haemorrhagins. This combination of venom results in death in only a few hours. These snakes are also very aggressive and have large fangs, so that if one is crossed it will strike. These snakes are terrestrial and their appearance match the ground cover. They are usually light brown with darker brown spots on there sides. The spots are usually large and bordered by a white ring. They have five white stripes that radiate from the tip of there head.
The next group of pitvipers is from the genus Bothriechis. These snakes are the palm pitvipers. They are called this because many species tend to reside in smaller palms. There are seven species of palm pitvipers. All of them are arboreal and are very thin. They are usually shorter than a meter. They all have vertical pupils. Palm pitvipers reside on highlands in tropical forests. These vipersÕs venom is not deadly. It causes cell death, which at worst leads to necrosis or amputation of a limb. While there bite isnÕt as bad as some vipers, treatment should be started immediately after the bite.
There are three species of Palm pitvipers in Costa Rica. Bothriechis lateralis is known as the side-striped palm-pitviper. These vipers live at higher altitude rainforests and wet forest. They are slender, with a prehensile tail that helps them climb. Side-striped palm pitvipers are green with vertical stripes starting at their backbone and stopping about half way down their sides. These may be smaller or not present in adults. The juveniles begin life brown with a yellow tail and change green. These snakes seem to be found more readily by water. This is most likely because of their diet, which includes lizards and amphibians. The second species of palm pitvipers is B. nigroviridis. These are Black-speckled palm pitvipers. They are green or yellowish and mottled with black specks. They have a distinct black stripe behind their eyes. They feed on lizard, frogs, small birds, and rodents. They have a painful bite and have been recorded to cause human fatalities. They reside at high altitude forests and cloud forests in central Costa Rica. They already have a small habitat and with destruction of parts of the forests they are struggling to survive. This species is very rare and endangered because of habitat destruction. The final species of palm pitvipers is the well-known B. schlegelii. They are better known as eyelash palm pitvipers. B. schlegelii gets its name from the distinct scales above their eyes, ÒeyelashesÓ. These are the most widespread palm pitvipers in Central America. These snakes are found on the eastern side of Costa Rica in low rainforests. These are the only species of palm pitvipers that donÕt tolerate higher altitudes. Eyelash palm pitvipers are very diverse. They have varied colors, from yellow to green to brown. Yellow coloration is most commonly found in Costa Rica. There are rare fatalities, but there are many rumors about how deadly these snakes are, but they rarely bite and out of those bites only a few have ever resulted in death.
The genus Bothrops are lanceheads. There is only one species of Bothrops in Costa Rica. It is B. asper. It has two common names one is from Spanish, terciapelo, which means ÒvelvetÓ. The second is French, fer-de-lance, which means Òiron spear pointÓ. This species is throughout Central and South America. They are found in the Atlantic lowland rainforests of Costa Rica. They are restricted to areas near water. The adults are terrestrial and the juveniles are semi arboreal. They eat small mammals, bird, and lizards. Terciapelo have varied colors, but usually are brown with a dark brown stripe behind their eyes. They have bordered dark brown triangles on their sides. The juveniles have a yellow tip on their tail. Lanceheads are only active at night, and are usually out of sight during the day. These are one of the most common snakes in Central America. They are also one of the most dangerous. They account for 90% of all serious snakebites in Central America. They are very fast and unpredictable. They will strike whenever frightened. They have deadly venom with procoagulants, myotoxins, and cytotoxins. Their venom, speed, and unpredictability make them a very deadly snake.
There is one kind of rattlesnake in Costa Rica. It is the Neotropical rattlesnake (Crotalus durissus). It is brown with upside down triangles of darker brown and a brown stripe on its dorsal. They eat small mammals, birds, and lizards. It lives on the west side of Costa Rica in the tropical dry forest. This species ranges all the way to Argentina. These different populations have different appearances and venom. In Costa Rica the venom is mostly procoagulants, haemorrhagins, and cytotoxins. They rarely case serious bites and warn any predator with their rattle well before they strike.
Lachesis melanocephala is known as the black-headed bushmaster. It is the largest species of pitviper in Costa Rica. It is also the only species of pitviper that lays eggs instead of giving birth to live offspring. It is found on the Pacific side of Costa Rica in the rainforest. They are nocturnal and rarely bite humans. If bitten it is almost always fatal. There venom is an anticoagulant and haemorrhagins. Visitors to the rainforest rarely see them because they are only active at night.
The last genus of pitvipers that reside in Costa Rica are Porthidiums. These are terrestrial pitvipers. They are usually small and fat. They produce very little venom because of there size. There have been very few fatalities due to these snakes. There are 5 species of Porthidiums in Costa Rica. The first is P. godmani or GodmanÕs montane pitviper. This species lives at higher elevations in cloud forests and pine oak forests. They are usually brown or reddish brown, with blotches and a dorsal stripe that zigzags down the back. They are active during the day and are frequently seen. This species venom isnÕt fatal. There are no reported deaths from this species and the worst case resulted in necrosis of a digit. Another species that is known to cause a few fatalities from this genus is P. nasutum. The rainforest hognosed pitviper is more venomous than other Porthidiums, but is only responsible for a few deaths. These snakes are unique because their snout is curved upward. They are tan or light brown with a pale stripe that follows their vertebrae. These vipers have brown blotches on their sides. They are small and stout like others in their genus. Like P. godmani they are active during the day. It has also been seen during the evening. These snakes eat rodents and small bird and are able to climb trees, although they are primarily terrestrial.
There are three other Porthidiums in Costa Rica. P. nummifer are also called jumping pitvipers. Their name refers to the myth that they are able to strike the full length of their body. They actually can only strike as far as a little more than half their body. This species is stout and short, so its strike distance isnÕt very far. They are usually not aggressive and have short fangs. The venom of these vipers doesnÕt cause serious illness and only result in localized pain and swelling. Jumping pitvipers are dark brown with a brown stripe behind their eye and dark triangular spots on their back. This species is nocturnal. P. ophryomegas is also a nocturnal snake. Its common name is slender hognosed pitviper. It is smaller and thinner than the hognosed pitviper. It is tan or gray and has a white or yellow stripe down its back, with small blotches just on the dorsal side of the snake. These snakes are aggressive and strike readily. They are very active during the wet season in tropical dry forests. The final species is P. picadoi. This species habitat is in the center of Costa Rica at varied altitudes. They live in wet forests. They have thick bodies, but are the longest of this genus. They are calm and are rare to come by.
All of Costa RicaÕs venomous snakes are important to the ecosystem. They have evolved to perfectly match their environment. They deserve to be respected and protected.
Beletsky, L. (2005). TravelersÕ Wildlife Guide: Costa Rica. Northampton, MA: Interlink Books.
Campbell, J.A. and Lamar, W.W. (1993). The Venomous Reptiles of Latin America. Ithaca, NY: Comstock Publishing Associates.
Collins, J. and Seigel, R. (1993). Snakes: Ecology and Behavior. New York: McGraw -Hill, Inc.
Greene, H.W. (1997). Snakes: The Evolution of Mystery in Nature. Berkeley: University of California Press.
Kricher, J. (1999). A Neotropical Companion. Princeton: Princeton University Press.
Milton, S.A. and Milton, M.R. (1980). Venomous Snakes. New York: Charles ScriberÕs Sons.
OÕShea, M. (2005). Venomous Snakes of the World. Princeton: Princeton Press.
Savage, J. 2002. The Amphibians and Reptiles of Costa Rica. Chicago: University of Chicago Press.
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