The fen raft spider is one of the largest spider species in Europe and the biggest in the UK. Until recently it was thought to be endangered in the UK but thanks to some introduction projects its numbers have increased.
Spiders are commonly overlooked in conservation as people generally freak out about the return of arachnids. The impact of the return of this species is a bit of an unknown as although they were thought to be endangered, no one truly knows how many there were to begin with. Their extreme rarity led to an assumption they were endangered and they were reintroduced to several locations, such as an RSPB site in the Norfolk Broads, in 2012.
The spiders live in ditches and pools as their large legs allow them to float on the surface of the water. They are semi-aquatic and have been known to hunt sticklebacks and tadpoles although they commonly hunt pond skaters and small flies.
Their return is good news for conservation as they are one of only three spiders species which receive legal protection in the UK, the others being the ladybird spider and the horrid ground weaver. Spiders are vital in ecosystems and do require protection despite their unpopularity. Recent scare mongering concerning the false widow has done little to boost the image of the spider but raft spiders are completely harmless. They can have bodies up to around 2.5cm and a leg span of up to 7cm but have no interest in humans and no ability to harm us.
The spiders are surveyed by counting their nursery webs, webs where their eggs are laid. There were over 1000 found this year which is more than double what was found last year. Each spider can lay up to 700 eggs though very few survive.
The spiders were reintroduced to the area by being hand reared in captivity. Young spiders (spiderlings) were placed in test tubes and individually fed fruit flies every 4 days until they became large enough to survive on their own. 200 spiders were raised like this in Chessington Zoo and then released in a variety of sites in 2012.
The locations for the spiders in England and Wales are given in the link below should you wish to take a look.
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