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What was the largest spider in history?

Spiders come in all shapes and sizes, from tiny jumping spiders to large tarantulas. But what was the largest spider to ever exist? In this article, we’ll explore the biggest spiders throughout history and what made them so large.

Megarachne servinei

One of the largest spiders to ever exist was Megarachne servinei, an ancient relative of modern spiders that lived about 300 million years ago during the Carboniferous period. Based on its fossilized remains, researchers estimate Megarachne had a leg span of around 2.5 feet (around 75 cm).

Megarachne was discovered in Argentina in the 1980s. The fossil reveals an eurypterid, an extinct group of aquatic arthropods that are closely related to arachnids. Megarachne likely lived in swampy, humid forests near coastal plains, feeding on smaller invertebrates and even small amphibians and reptiles.

For years after its discovery, Megarachne was thought to be a sea scorpion. But closer examination of its anatomy in the 2000s revealed it was actually more closely aligned with spiders. With its massive body size and leg span, Megarachne would have been a formidable predator during the Carboniferous.

Physical characteristics

Based on the Megarachne fossil, here are some of its key physical characteristics:

  • Estimated leg span of 2.5 feet (75 cm)
  • Oval-shaped abdomen
  • Long front appendages with spikes likely used for grasping prey
  • Powerful jaws and mouthparts
  • Long tail-like structure extending from the abdomen

Other giant prehistoric spiders

While Megarachne is considered the largest fossilized spider, there are a few other contenders for giant prehistoric arachnids:

Mongolarachne jurassica

Mongolarachne jurassica is another ancient giant spider that lived about 165 million years ago during the Jurassic period. It was discovered in Inner Mongolia and is estimated to have a leg span of nearly 6 inches (15 cm).

Nephila jurassica

Nephila jurassica is an extinct species of golden orb-weaver spider that lived about 165 million years ago. Fossils show it had a leg span of up to 5 inches (15 cm) across.

Jaxtasuchus extremius

Jaxtasuchus extremius is an extinct species dating to about 95 million years ago during the Late Cretaceous. This prehistoric spider is estimated to have a leg span of 8-9 inches (20-23 cm) across.

The largest spiders today

While not quite as massive as some prehistoric spiders, there are a number of large spider species alive today. Here are a few of the current record holders for biggest spider leg span:

Spider Leg Span
Goliath birdeater 12 inches (30 cm)
Giant huntsman spider 12 inches (30 cm)
Colombian giant tarantula 11 inches (28 cm)
Brazillian salmon pink birdeater 11 inches (28 cm)

Goliath birdeater

The Goliath birdeater (Theraphosa blondi) is the largest spider in the world by mass, weighing up to 6 oz (170 g). Found in northern South America, the Goliath birdeater gets its name from its occasional habit of feeding on birds in addition to its normal diet of insects and other invertebrates. They have a maximum leg span around 12 inches (30 cm).

Giant huntsman spider

The giant huntsman spider (Heteropoda maxima) also has an impressive leg span approaching 12 inches (30 cm). Found in Laos, it is a member of the Sparassidae family of huntsman spiders. Its enormous size allows it to feed on small vertebrates including geckos and birds.

Colombian giant tarantula

The Colombian giant tarantula (Megaphobema robustum) can attain leg spans over 11 inches (28 cm). Found in northern South America, it lives in burrows in swampy forest areas, feeding primarily on insects, other arthropods, and small vertebrates.

Why were prehistoric spiders so large?

There are a few theorized reasons why spiders like Megarachne and other prehistoric arachnids were able to grow to such massive sizes:

  • Higher oxygen levels – During the Carboniferous and other prehistoric periods, global oxygen levels were much higher compared to today. This allowed arthropods and other creatures to grow to larger sizes.
  • Warmer climate – Warmer climates during the Carboniferous and Mesozoic supported larger invertebrates.
  • Abundant prey – Large swampy forests and jungles provided plentiful prey, supporting the growth of giant spiders and other predators.
  • Lack of predators – With few or no large predators like birds and mammals, giant spiders could thrive.

Could giant spiders exist today?

The largest spiders today are smaller than many of their prehistoric ancestors due to different environmental conditions. However, its theoretically possible giant spiders could exist in today’s environments under the right circumstances:

  • On isolated islands or in remote habitats lacking predators, very large spiders and insects can evolve through selective pressures.
  • With climate change impacting ecosystems, larger spider species may adapt and grow bigger in certain tropical environments.
  • Genetic engineering could theoretically produce larger spiders, though there are currently no plans to try this.

However, it’s unlikely any modern spiders will match Megarachne and other prehistoric spiders in scale anytime soon. The environmental and ecological conditions that allowed ancient spiders to grow so massive simply don’t exist today.


Megarachne servinei remains the largest known spider to have existed based on its impressive 2.5 foot leg span. This massive prehistoric spider lived around 300 million years ago during the Carboniferous period and filled an ecological niche preying on other invertebrates and small vertebrates in steamy ancient forests. While no living spiders are quite as big as Megarachne, some species like the Goliath birdeater can attain leg spans over a foot across. Ancient spiders could grow to epic proportions thanks to environmental factors like high oxygen and ideal climate conditions supporting large invertebrate life.