04/09/2019

World’s rarest spider born at Bristol Zoo Gardens

For the second time, we have successfully bred some of the rarest spiders on earth.

The milestone for the species is even more significant because keepers have had to incubate a clutch of eggs after a mother recently died. 

Over five hundred Critically Endangered Desertas wolf spiderlings have been born to two female spiders inside our very own Bug World – boosting the world’s once dwindling population.

The new babies who are just 4mm in diameter are expected to grow to around 12cm by the time they’re adults. 

The mothers of the spiderlings were among the first to be born in captivity in the world.

They were born at the Zoo after around 25 were brought back to England from Portugal to establish the world’s first captive breeding group for the species.

In the wild the species are only found in the Castanheira Valley on one of Madeira’s Desertas islands.

Their main threat is the spread of a grass in the genus ‘Phalaris’, which covers soil and rocks making micro habits beneath them harder for the spiders to access. 

Our invertebrate curator, Mark Bushell, brought the spiders back from Madeira and he and his team have gone on to successfully reproduce them and send a number to other European zoos as part of the breeding programme.  

Mark said: “This is such a huge achievement for everyone involved. We’ve learnt so much about the care and conditions required for breeding from our first generation of wolf spiders and to now have welcomed a second generation is a massive success.

“All spiderlings are eating well and have begun dispersing from their burrow. A large number are still on their mother’s back, where she has carried them since they were in the egg sac. It won’t be long before they start to fend for themselves.”

The eggs that were produced by the mother who died are being cared for by Mark’s team.

“The process requires careful management of the tiny eggs, which are no bigger than a grain of cous cous, including separating eggs that get stuck together and turning eggs to ensure their conditions mimic those that the mum would provide,” Mark explained. 

“It’s vital that we raise awareness of the importance and uniqueness of these spiders and these descendants of the world’s first ‘safety net’ population are helping us to do this.

“When we think of species that are becoming extinct we often think of larger animals, but invertebrates, many of whom play a crucial role in the world’s ecological balance, are also at great risk,” he added. 

Bristol Zoological Society is participating in a five year Desertas wolf spider strategy, along with participants from the Regional Directorate of Environment, Madeira Natural Park Services (two bodies that have now merged under the Institute of Forests and Conservation of Nature - IFCN), the University of Madeira and the IUCN Species Survival Commission, and coordinates the ex-situ programme to boost the wolf spider population, with other partner zoos in Europe. 

The objectives of the programme include restoring the ecological balance in the Castanheira Valley through reduction of Phalaris density on the assumption that a viable population of spiders will persist across the entire valley.

Others include analysing the genetic structure of the spider’s population, its habitat preferences and the potential consequences of climate change, and to raise awareness of the importance and uniqueness of the spider to Zoo visitors. 

Find out more about Bug World.

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