Mexico has a large biodiversity, which also includes some of the deadliest animals in the world.
The deadliest animals in Mexico include two types of snakes, two spider species, and a lizard.
With the help of Dr. Alejandro Alagón Cano, an expert on venom who is renown for his work in the development and improvement of antidotes, Tangible ranked the 7 most poisonous terrestrial animals in Mexico.
7. Black Widow
Scientists know it as Latrodectus mactans and although its venom is not lethal for humans, one of its bites can cause some of the worst pains. The black widow is one of the two spider species present in Mexico, whose venom affects humans, out of the 2,500 spider species that have been found in the country.
Luckily, it is a shy insect and easily recognized, mainly the females, who have a shiny red hourglass mark. According to an alert issued by Mexico's Social Security Institute (IMSS) in 2018, the states where there is a higher risk of being bitten by a black widow are Coahuila, Chihuahua, Tamaulipas, San Luis Potosí, and Nuevo León. The number of cases increased during winter for a simple reason: the spiders look for shelter during the cold and enter homes.
The black widow only attacks humans when it feels threatened, especially if it perceives someone or something is pressing it against someone's skin. Their venom is deadly for other insects, their main source of food. In the case of humans, the bite has neurotoxic effects and can result in intense muscle pain, cramps so bad they are often confused with appendicitis, hypertension, and excessive sweating. Although the person has a tough time, they will recover.
6. Gila monster
Alejandro Alagón says that the “Gila monster is my favorite bug” who says he “wrote my Ph.D. thesis on the characteristic of some of the components of its venom.” These lizards from northern Mexico, named Heloderma suspectum, is quite rare because it and its neighbor, the Mexican beaded lizard, known as Heloderma horridum, are the only two venomous lizards in Mexico and the world, out of the 5,000 species in the world. The venom is a powerful toxin cocktail but the few accidents involving its poison landed it in the sixth place in this list.
The Gila monster is rarely aggressive and quite slow; they can measure up to 60 centimeters long and inhabit semi-arid ecosystems. They feed on the eggs of others vertebrates but when they hunt, they bite the victim and release their venom between its teeth and into the wound. This mixture of substances, produced by its modified salivary glands located in the lower jaw, which is also used as a defense mechanism. According to biologist Fanti Echegoyen, who works at the Botany and Zoology Department at the Guadalajara University, the Gila monster's venom contains several components, including exendin-4, which has hypoglycemic effects, which means it reduced the glucose levels in blood; therefore, it's being used for the development of new drugs against diabetes type II.
5. Coral snake
There is a myth surrounding Mexican coral snakes, which increases the danger. It's been said that those who are truly venomous, the Micruroides and Micrurus, have a color pattern, black stripes followed by yellow stripes, which distinguishes them from other snakes or “fake coral snakes”, who supposedly have black stripes followed by red stripes. This myth comes from herpetology books form the U.S., where the diversity of these species is lower than in Mexico.
In fact, in Mexico, there are 16 species of coral snakes and other 40 similar species but there are quite inoffensive; in some places, it's possible to find an identical snake for every venomous species. For this reason, if you are not a snake expert, you should stay away from them.
The coral snakes aren't snakes, they belong to another serpent species, the elapid snakes, including the black mamba and cobras. In regards to its venom, Alagón Cano, who has been named an emeritus researchers at the National Autonomous University of Mexico, explains that its venom is an adaptation of its eating habits: “The coral snakes feed on lizards and other serpents, therefore, the majority of the components in its venom effect these organisms.” Nevertheless, some of its alpha-and-beta-neurotoxins can seriously affect mammals, humans among them. The alpha-neurotoxins block the acetylcholine receptor in the nerve cells, while the beta-neurotoxins prevent the release of said neurotransmitter; in the end, there will be an interference in the neuromuscular activity. A person who has been bitten by a coral snake will present paralysis, and in the worst case scenario, a cardiopulmonary arrest. The good news is that according to the Health Ministry, only 4% of the ophidian accidents, snake bites, in Mexico are caused by coral snakes.
4. Chilean recluse spider
Along with the black widow, the Chilean recluse spider is the only spider in Mexico with fangs able to pierce human skin and inject its venom. This is Dr. Alejandro Alagón's favorite venom, perhaps because it is so efficient that only one of its components is responsible for the intoxication of humans and “the rest of the substances cause paralysis in insects, which are the main preys of these spiders.” The component is Sphingomyelinase D, a protein that produces the formation of a blisters hours after the bite, which later destroys skin cells close to the bite, killing the skin tissue. When the intoxication is on the skin, it is called local loxoscelism; nevertheless, clinical data mentions that 10% of the cases of the spider bite show are systematic loxoscelism, which causes metabolic disorders, kidney damage, and severe lung damage, coagulation disorders, hemolytic anemia, and death.
The issue with the brown spider is that it is usually confused with long-bodied cellar spiders and with other small and inoffensive brown spiders. It is possible to identify them because they have a mark that resembles an inverted violin on their backs. To prevent being bitten by one of these spiders, you have to clean all the spider webs, dust clothes, and shoes before wearing them.
There are around 37 rattlesnakes species in the world and Mexico has the largest diversity of these reptiles from the Crotalus genus. In fact, 92% of rattlesnakes inhabit Mexico and at least 22 species are endemic from Mexico. The Crotalus serpents are responsible for 44.9% of snake bites in the country, according to a 2013 study, which is difficult to treat because there are a lot of symptoms. “The rattlesnakes have some of the most complex venoms you could find, with hundreds of components,” explains Alejandro Alagón, who leads a laboratory in the UNAM'S Biotechnology Institute, “for example, doctors sometimes report neurotoxic effects and sometimes they don't; that's why my students have analyzed the venom from different species in different geographical locations, to make a map of the potential risk of neurotoxicity according to the location where the bite took place.”
Luckily, rattlesnakes prevent their potential victims with their sound. In the case of their preys, they quickly bite, inject venom with their powerful mobile fangs and then release them. That is enough to paralyze the victim in seconds, thanks to two proteins: croxotin and crotamine. In humans, the venom of the rattlesnakes affects the nervous system and muscles; also, it produces coagulation disorders, hypertension, and damages the area surrounding the bite with blisters and hemorrhages. Luckily, this poisoning rarely kills the muscle tissue, as in the case of other serpents in Mexico.
“I was bitten by a scorpion at home," said Dr. Alagón, “first I endured it, to see what happened; I couldn't talk because of the numbing of my tongue; I threw up three times, and each time it was very hard to breath; in the end I injected the antivenin but all that was horrible.” What happened to Alagón Cano was that a few components, out of the hundreds of components in the scorpion venom, produced a neuromotor syndrome in the autonomous nervous system. These toxins can cause death, especially in children: “what it does is opening the sodium channels, altering the management if the electric current in the excitable cells; then hyperexcitability is produced from those cells (…) people can experience involuntary movements, salivation or dry mouth, dilated or contracted pupils, fibrillations, muscular paralysis, bronchial hypersecretion, gastric secretion, vomit; there are many symptoms,” said Dr. Alagón.
According to the academic, the intoxication from a scorpion sting is the main public health issue associated with venomous animals in Mexico, also, 300,000 cases are reported each year, compared to very few snake bites reported. In Mexico, there are over 200 scorpion species; they are all venomous but only a dozen of them are dangerous for humans. Scorpion stings can be treated with Alacramyn, an antidote developed by Mexican scientists, including Alejandro Alagón.
1. Fer-de-lance serpent
The fer-de-lance serpent could be anyone's worst nightmare. “I've never seen once,” Alagón remembers, “but I met a man who was bitten by one; his names was Ramón, he worked as a gardener in a ranch owned by my grandfather located in Puebla (…) that's where my story with venoms began, I asked him to tell me about the bite,” According to Alagón Cano, Ramón was bitten by a fer-de-lance two kilometers away from the town, and although he was able to return to the ranch by himself, he was almost fainted as a result of the hypothermia caused by the venom. The toxins form the so called Bothrops asper killed Ramón's muscle tissue, it destroyed the gastrocnemius muscle on one of his legs: “this left him with a certain disability but there are people who lose limbs, either legs or arms,” says the UNAM expert, “also, with a snakebite from the fer-de-lance, people can bleed from everywhere, from their gums, esophagus, intestine, stomach, there can be a brain hemorrhage.”
The fer-de-lance is a very large snake and quite nervous, therefore, it attacks more frequently. It also inhabits a large area in the country, throughout the Gulf of Mexico, from southern Tamaulipas to Yucatán and Chiapas, according to information from the National Commission for the Knowledge and Use of Biodiversity (CONABIO), this species is responsible for 42.8% of snake bites in Mexico. In contrast with other venomous species, this one is unpredictable and excitable.
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