Another big one – Britain’s Heaviest Spider

Flanders Moss NNR

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There is a bit of a theme here but here is another whopping great insect I came across last week, like the last blog post.

This is the 4-spot spider, a common spider and heaviest found in the UK; that is the species not just this individual! It had a web formed on the back of a plastic piling dam that I was lowering so I did cause it a bit of disturbance but it moved back into position once I had finished.

These spiders are common and weave low webs often with the aim of catching hopping insects such as bugs and grasshoppers. And here was its dinner, a nice plump grasshopper and also a small bug all wrapped up and prepared for later delectation.

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These spiders are big enough to actually munch their prey unlike other species who inject digestive juices and then slurp the resulting soup. And these 4-spot spiders also eat the silk thread that they have wrapped their prey to immobilize it and apparently very quickly recycle it back into more silk.

There is a suggestion that 4-spots can change their colour to match their background though this maybe just a change due to differences in humidity. Either way they can be very variable in colour. This beast is a female and is so large because she is developing eggs in her pendulous body. She can lay up to 900 eggs wrapped in a silk cocoon which overwinter and then hatch out in the spring. These spiders must be fantastic feeders as after hatching from eggs in April they grow from about 1mg to an adult weight of up to 2.5g and near the end of the growth period they can put on up to 10mg / a day. That is impressive eating.

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