UK’s biggest spider reintroduced into Norfolk

The great raft spider (Dolomedes plantarius) has been bred for reintroduction to its former habitat in the Norfolk Broads. The 5mm spiderlings have been released at the RSPB’s Strumpshaw Fen reserve near Norwich, UK.

The great raft spider gliding © Helen Smith

The great raft spider gliding © Helen Smith

The project, lead by an ecologist Dr Helen Smith who has been working with fen raft spiders for 20 years, as a part of Natural England’s Species Recovery Programme, aims to revive the three remaining populations of this water-gliding arachnid species that live only in wetlands and to give them the best chance to survive in the wild. It should also raise awareness on the significance of wetland habitats and other vulnerable invertebrates.

The fight for this species started as her effort to hand-rear spiders in her kitchen back in 2010. In October 2010, the first 1,600 of these spiderlings have been released into suitable dykes at Castle Marshes reserve near Beccles, Suffolk. They were hybrids between Sussex and Suffolk populations. “The hybrids bring the advantage of increased genetic variability to the new population,” said Dr Smith. “This… should give the new population at Castle Marshes the best potential to adapt to its surroundings and to cope with the impacts of climate change.” In addition, in October last year, 200 spiders have been released in the protected Pevensey Marshes in Sussex.

The milestone of Dr Smith’s project was reached in July this year when it was reported that spiders released in Castle Marshes have started to breed. Four female adult nursery webs, with more than 200 spiderlings each, have been found on water soldier plants. By this date, Dr Smith has hand-reared about 3,000 spiders in individual test tubes until they have aged three months. The spiderlings have also been released in other parts of Waveney valley – Carlton Marshes and Redgrave & Lopham Fen.

The latest release of this “beautiful but extremely rare spider” with a leg span of up to 8 cm in Strumpshaw Fen reserve near Norwich, as Dr Smith says, is being made in the third year of the translocation project, funded by Natural England, the Broads Authority and the BBC Wildlife Fund. Eggs were collected from Redgrave and Lopham Fen reserves in Suffolk and distributed to 10 zoos nationwide where an army of willing volunteers have been taking care of their growth.

The babies were bred in individual test tubes away from wetland plants and a simulation of natural environment. They have also been fed with a specific diet of flies in order to avoid predatory feeding on each others. This was done so that the survival chance of these little spiders could be increased by almost 90% which would allow them a higher success rate in the wild.

As these spiders are predators that are even known to eat the prey larger than themselves, the scientists are consistent in their decision to translocate this species only in the most stable and biodiverse wetland ecosystems, such as those that have recovered from the intensive agricultural use. “This is never going to be a common species, it’s always going to be consigned to our best wetlands,” said Dr Smith.

“Translocation isn’t the answer to all our species-loss problems,” said Dr Smith. “You can’t put most things back – but for some of them, it’s worth doing.”

Source: BBC