How tarantulas conquered Earth
Mindy Weisberger
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Tarantulas, everyone’s favourite hairy spiders, are found worldwide, inhabiting all continents except Antarctica. But how did they become so widespread? To answer this question, researchers went looking for the origins of the tarantula group more than 100 million years ago, building a tarantula family tree based on molecular clues from existing databases. Once they created the tree, they mapped it to a timeline of spider fossils to estimate when – and where – tarantulas appeared and dispersed.
The scientists discovered that tarantulas first emerged during the Cretaceous Period in what is now the Americas. But at the time the Americas were part of the massive supercontinent Gondwana. Ancient tarantula relatives, even if they were homebodies like tarantulas today, likely spread across the joined landmasses, dispersing from the Americas into Africa, Australia and India. Then, after Gondwana broke apart, India separated from Madagascar and collided with Asia, bringing the hairy spiders to that continent, too.
There are only two known tarantula fossils, both preserved in amber: one is from Mexico and is thought to be around 16 million years old, and the other is from Myanmar and is about 100 million years old. Because tarantula fossils are so rare, researchers also collected data from related mygalomorphae, the arachnid group that includes tarantulas and other big grounddwelling spiders, which are better represented in the fossil record than tarantulas.
After constructing a family tree for tarantulas, representing 29 tarantula species and 18 other mygalomorphae, the scientists time-calibrated the tree using data from fossils. This enabled the researchers to calculate the ages of tarantula lineages and approximate when the ancestors of modern tarantulas spread over the world.
This new timeline revealed that tarantulas first appeared in the Americas about 120 million years ago. There, the spiders that were ancestors to Africa’s tarantulas emerged around 112 million to 108 million years ago. By about 108 million years ago, tarantulas were established in what is now India. India separated from Madagascar between 95 million and 84 million years ago, drifting towards Asia. That slow-motion collision, which began between 58 million and 35 million years ago, brought tarantulas to the Asian continent.
However, before that happened, India’s tarantulas diverged into two lineages with different lifestyles: one group of tarantulas were predominantly tree-dwellers, and the other mostly preferred life in burrows.