Snakes are thought to have evolved from lizards, with the first specimens appearing in the fossil record during the Jurassic Period, between 143 and 167 million years ago. They diversified and modern snakes emerged after the extinction of the dinosaurs, 66 million years ago.
There are now more than 3,000 species of snake on the planet, with 600 of these being venomous.
They one of the most dangerous animals on Earth. The World Health Organization estimates that between 80,000 and 138,000 people die from snake bites each year.
According to National Geographic, snakes can be everywhere in the world except in Antarctica, Iceland, Ireland, Greenland, and New Zealand.
The size of snakes varies widely between species, with the smallest measuring just four inches in length. But what of the biggest?
The longest snake
Graham Alexander, professor of herpetology at the University of Johannesburg, South Africa, told Newsweek that estimates of how long a snake is should always be taken "with a pinch of salt," as they are often exaggerated.
However, he said that no other snake can compete with the length of the reticulated python. "I've seen reticulated pythons in Southeast Asia that were significantly over 19 feet feet," he said. "They are massive snakes, without exaggerating."
The reticulated pythons average length is 20 feet, making it the longest snake in the world.
It is native to South and Southeast Asia and can be found in rainforests, woodlands, and nearby grasslands. The python is a good swimmer and has in some instances been found far out to sea.
Alexander said: "We should remember that captive specimens may have the potential to reach larger sizes than wild ones on account of a steady food supply and a lack of predation in captivity.
"I do know that there are a couple of cases of Burmese python and reticulated python reaching lengths of around 26 feet in captivity. These are truly exceptional."
Pythons are non-venomous and kill their prey by suffocation. They use the momentum of a strike to wrap themselves around their victim, squeezing a little more tightly every time the prey exhales.
Alexander said that while pythons can be huge in length, the danger they pose tends to depend on their evolutionary history with humans: "Giant pythons in Asia, such as Burmese and reticulated Pythons, may on occasion view humans as a potential meal. They have not had the long evolutionary history with humans as African pythons have.
"In my opinion, African pythons exclude humans as prey because humans are just too dangerous—pythons that take humans usually end up dead, which has selected that taste out of the population. As with anecdotal reports on giant snakes in general, there is a lot of exaggeration."
The heaviest snake
In terms of mass, there is no beating the green anaconda.
A member of the boa family, green anacondas are non-venomous and use their strong jaws to capture their prey. They then suffocate it before swallowing it whole.
They are also highly aquatic and spend nearly all their time in water. According to Alexander, green anacondas can exceed 220 pounds on occasion and reach up to 16 feet in length.
"There will probably be exceptional individuals that are significantly larger but I do not believe reports of 10m [32.8ft] snakes in the wild," he said.
"In my opinion, I would not think that anacondas have humans on their menus since anacondas, especially large individuals, tend to ambush from water in swampy wetlands and so the potential for meeting humans there is slim, unless the humans are researchers specifically looking for the snakes."
The biggest venomous snake
Venomous snakes tend to be smaller in size as they don't have to rely on suffocating their pray.
Alexander said the king cobra is one of the world's largest venomous snakes, growing on average up to 13 feet. There have been some reports, however, of it growing up to 18 feet.
King cobras in live in South and Southeast Asia, and are classed as vulnerable with their population decreasing, Despite having an aggressive reputation, the king cobra is actually much more cautious than many smaller snakes.
The king cobra, like many other snakes, only attacks people when it is cornered, in self-defense or to protect its eggs. Its venom however, can be fatal. Depending on the potency of the venom and how big the victim is, it can kill within 15 minutes.
The black mamba is another one of the world's longest venomous snakes and one of the most dangerous snakes in the world.
Nick Evans, founder of the KwaZulu-Natal Amphibian and Reptile Conservation, in Durban, South Africa, told Newsweek that the black mamba is the longest snake he has ever come across, usually measuring around nine feet. There are records of them growing to 14 feet, however Evans said this is rare.
Black mambas reside in South and East African savannas, rocky hills and open woodlands, however with many residential areas being among valleys, this often means they can be found in and around homes.
Evans said that they are extremely misunderstood creatures.
"Before working with them, I was always a bit scared of them. I had obviously heard lots about their fearsome reputation. However, after learning to work with them, and having worked with a few hundred, I can now see what they're really like, that their reputation is very over-exaggerated," he said.
"They're known for being super aggressive killers. Yes, their neurotoxic venom certainly can be fatal. However, they're far from aggressive. I am constantly chasing them, they're not chasing me ... the problems start when people try to kill them, or catch them without training."
