Spiders first evolved around 400 million years ago, and some of the eight-legged wonders that appeared all that time ago are also similar to some of the largest seen on earth to this very today.
PhD candidate Anna Holmquist, who researches arachnology at the University of California, in Berkley, told Newsweek that it made sense for spiders to be really large 400 million years ago.
"The majority of the spiders that evolved during this time live underground, they build burrows and don't build webs. They have more of an active hunting strategy, which was most effective strategy at the time, when animals were typically much larger," she said.
Holmquist said over time, more spider species began adapting to building webs—a hunting strategy that benefited them when they became smaller.
While these large spiders may also have decreased in size over time, they still remain enormous and are widely feared.
So, what are the world's biggest spiders? And, is the fear justified?
Goliath Bird Eater
Holmquist said the "classic example" of the world's biggest spider is the Theraphosa blondi, a type of tarantula more commonly known as the Goliath Bird Eater.
This is the biggest spider in the world based on body mass, Holmquist said. Its leg span can reach up to 12 inches and it can weigh up to 6 ounces. It is native to South American rainforests and can be found in burrows or lurking beneath rocks.
Unlike other spiders, it does not spin a web to catch food, rather, it is an ambush predator, and lies in wait for prey to come close.
"They call it the bird eater, but it's really just a term used to describe these large tarantulas. They can eat birds, but that is quite rare," Holmquist said.
These spiders usually eat earthworms and beetles, and sometimes even larger animals such as toads. They may also feast on larger rodents, such as mice.
While these spiders are huge and venomous, Holmquist said they tend to be misunderstood.
"One of the biggest misconceptions with this spider is that because they are so big, they must be deadly, but that's not true at all. They have venom, but it isn't harmful to humans and it's not really possible to die from it," she said.
The Giant Huntsman
Another of the world's largest spiders is the Giant Huntsman Spider.
"Huntsman spiders are really common globally, but in Southeast Asia and Australia, you get some really, really big huntsman spiders. This is mostly based on their leg span. So this is technically the world's largest spider if you are looking at how long they are in total," Holmquist said.
The leg span of these spiders can reach 12 inches. People commonly mix them up with tarantulas, but they are actually from the sparassidae family. They can be told apart by the way they position their legs. Unlike tarantulas, Huntsman spiders tend to hold their legs in a crab-like posture.
These spiders can be found lurking under loose bark on trees, under rocks and on foliage.
Similar to the Goliath Bird Eaters, Huntsman spiders don't build webs to catch their prey. Instead, they run after their prey and ambush it. They usually eat larger insects such as cockroaches, then shut the prey down with venom.
Brazilian Salmon Pink Bird Eater Spider
With a leg span of up to 10 inches, the Brazilian salmon pink bird eater is considered to be the third largest spider in the world.
Another type of tarantula, this spider is known for growing quickly—it can grow to six inches in the first year of its life.
These spiders live in tropical Brazilian rainforests, and as its name suggests, it has pink hairs around its body.
These spiders, again, do not spin webs. Similar to the Goliath Bird Eater and the Huntsman, they lie in wait for their prey, and ambush.
While similar to the Goliath bird eater, it's name is slightly misleading. While it can feast on small birds, it usually sticks to insects.
Are They Scary?
Despite their monstrous size, there is little reason for humans to be afraid of these spiders, according to Fiona Cross, a New Zealand-based arachnologist.
Cross told Newsweek that spiders like this are "so often misunderstood."
"It might be easy to assume that these big spiders are dangerous to people because they are so big and have bigger fangs, but none these spiders are considered especially dangerous to people," Cross said.
"Most spiders use venom to immobilize their prey, but only about 0.5 percent of all spider species around the world are considered of medical significance to people, and they don't go out of their way to attack people."
Holmquist added that while these spiders are the largest scientists currently know of, in general, there is very little known about the species.
"Right now we have about 45,000 species of spider that we know of, but it's likely there are closer to 80 to 90,000 species out there. Whenever I go out into the fields I see massive spiders all the time, and there's very possibly, multiple other species that are even larger that we just don't see, or we haven't discovered yet," Holmquist said.