Some think it might have been an increase in Oxygen that caused them to grow large but not every-one agrees.

Here’s a couple of links that might be of interest.

When Giants Had Wings and 6 Legs

Atmospheric oxygen level and the evolution of insect body size

Megarachne was once thought to have been the biggest spider ever found but it has since been realised that it was a Eurypterid or Sea Scorpion. If it had been a spider it would have been quite large as it’s body estimated to be over 30cm in diameter.

Megarachne, the Giant Spider That Wasn’t

The true identity of the supposed giant fossil spider Megarachne

The Eurypterids could grow very large though.

Fossil of Biggest Bug Ever: 8 Feet Long

As far as large spiders go there are a few that are a fair size but the physics seem to be against any spider being really large unless it has evolved completely differently somehow from other spiders. It would somehow have to have an internal skeleton surely to be as large as some people are claiming.

Interesting link about some big spiders.

Nice little video clip.

The biggest spider I’ve seen had a leg span the size of my palm. This doesn’t sound like much but it is if you live in the UK.

Happy spider hunting.

actually i got on the computer to identify it and ended up on this site and made an account just to share this..

i live in southern louisiana, lafayette louisiana to be exact, i went in my backyard to cut my grass when i noticed a giant yellow web over a meter wide connecting my shed, my fence, and a tree. i checked it out for a while pretty amazed at it but didnt see a spider. I reached up and touched one of the thicker strands and noticed it was ridiculously strong. so i went in my shed, grabbed my hedge trimmers and cut a branch ab a 1/2 inch thick that had some web connected to it. the strands actually caught the branch and it just swung back and forth. then i looked up and saw what i have definately identified as a golden orb weaver spider with a leg span larger than my hand just sitting in a patch of leaves on one of the branches. it was actually quite beautiful, bright yellow and white with some red on it’s legs. I tried to take a picture of it with my phone but the only angle that didnt require me to stand directly beneath had the sun directly behind it and they wouldnt come out right..

it was then time to cut the grass so i grabbed my shovel out of the shed and knocked him out his web. This spider actually made a pretty loud thump when it hit the ground. at this point i got scared it would run at me or something and i chopped it in half with the shovel. :/ i went back later and located the tiny little male.

i promise im not blowing this up at all this spider was definately bigger than my hand and i could easily see it catching a bird in that web and it was more than big enough to eat it.

thanks

However,the discussion isn’t really arguing that, from what I understand the topic is about a giant spider that is yet unclassified, perhaps we could discuss how a spider could reach those lengths with adaptation and what that the most likely adaptations or changes in body structure that would entail. That would be insightful.

Anyhoo, on cryptozoology.com William J. Gibbons is quoted as saying (from his expedition report from the congo in search of Mokele Mbembe):

“In 1938, Mr. & Mrs. R.K. Lloyd of London, England were driving along a forest road in the former Belgian Congo, when they became aware of a large animate object moving across the road ahead of them. At first they took the object to be a large monkey or jungle cat. However, as they approached the creature, the Lloyd’s curiosity turned to horror as they came face-to-face with a gigantic brown spider. Mr. Lloyd attempted unsuccessfully to retrieve his camera as the giant arachnid simply walked into the forest and disappeared. On this third expedition to Equatorial Africa, I (Gibbons) took the opportunity to enquire if the pygmies knew of such a creature, and indeed they did! The Baka word for spider is Fofi (pronounced foo fee), and Jba means ‘great.’ They speak of the Jba Fofi, which is a ‘giant’ or ‘great spider’. They described a spider that is generally brown in color with a purple abdomen. They grow to quite an enormous size with a leg span of at least five feet. The giant arachnids weave together a lair made of leaves similar in shape to a traditional pygmy hut, and spin a circular web (said to be very strong) between two trees with a strand stretched across a game trail. These giant ground-dwelling spiders prey on the diminutive forest antelope (duiker), birds, and other small game, and are said to be extremely dangerous, not to mention highly venomous. The spiders are said to lay white, peanut-sized eggs in a cluster, and the pygmies give them a wide birth when encountered, but have killed them in the past. The giant spiders were once very common but are now a rare sight. Their dwindling numbers are blamed on the continuing deforestation of their habitat, but they are still encountered from time to time. The Baka chief, Timbo, casually mentioned to us that a giant spider had taken up residence in the forest just behind his village in November 2000, when I (Gibbons) and Dave Woetzel from New Hampshire had visited him! He did not think that we would have been interested in the creature as our interest was focused on Mokele-mbembe at the time! Valuable evidence had eluded us.”

I have heard that the louisiana spider doesn’t exist, but the J’ba Fofi (congo spider) does in fact exist, and reaches size of about 10 feet.

I don’t have any spider stories to share but I think it is important to point out the many personal experiences shared in this column by those who have encountered spiders (as well as other insects) of incredibly large size! I mean, we often accept the friend of a friend’s account about bigfoot, and we have here people who have witnessed first hand giant spiders! I realize and appreciate the argument that limit the size of such creatures and I don’t discount them, but are we absolutely sure that such creatures, no matter how improbable, cannot exist? Is it possible that some unknown biological adaptation might allow a spider to grow to such a large size? Spiders are, after all, one of the most successful species ever created, perhaps we should not too quickly dismiss such eyewitness descriptions?

I too think that spiders cannot really be compared with a terrestrial crustacean like the coconut crab. They have two very different body designs, and even with the coconut crab you are pushing the limits of the size a land arthropod could physically reach. Also, if anyone looks at how a coconut crab moves, they are not swift or stealthy at all. They are actually rather awkward and slow, precisely because they are so big, with heavy, unwieldy exoskeletons. You just are not going to get an arthropod that big scurrying around with any sort of speed.

In my opinion, based on the biology and physics involved, a spider is unlikely to get much bigger than the current record holders. Spiders the size of dogs or bigger are just not probable at all. It is exactly the same reason why I am very skeptical of giant spiders.

Nevertheless, deadx, your story has officially freaked me out. Thanks for the nightmares tonight.