Spiders, our unseen lodgers

by Pete Smithers

Standing on the roof of Exeter cathedral I am surveying the the city spread out below me as it runs out towards the Exe estuary. A sprawl of ancient and modern buildings that are a testament to the city's trading history. It is this history that brings a biologist to this stunning vantage point to discuss with the presenter of BBC Radio 4’s "Living World" why there are large spiders living in the Cathedral walls.  

The spider in question is Segestria florentina, a large spider (can be up to 2 cm in body length) that lives in silken tubes that it builds on holes and crevices in walls and rock faces. The entrance of the silken retreat possesses a number of trip lines that radiate from it giving the web a star-like appearance. These trip lines let the spider know when potential prey are close by and, when activated, the spider rushes out at incredible speed to claim its next meal. The lightening speed of this strike is disturbing but the flash of the spiders metallic green jaws make this an unforgettable experience when seen for the first time.  

So why are they in the Cathedral walls? The answer is trade. The spider is common in southern Europe and has been introduced to ports and market towns across southern England via trade in the 19th Century.  Thus, I find myself looking across Exeter city towards the Exe estuary, where once there was a thriving port that was a trading hub of the South West of England.

Descending the narrow spiral staircase to ground level we then hunted along the outer wall locating several Segestria. We tempted them into the open with tuning forks and an ultrasonic tooth brush but due to the rain that had set in by this time we did not manage to coax any all the way out of their holes. For the full story listen to the program which can be downloaded from the BBC i-player. The program was broadcast on Oct 27th.

2013 has been a good year for for raising the profile of spiders that live in walls and houses.  A recent BBC television programme, that focused on urban wildlife, featured a bug hunt with the local family-friendly natural history group "Wild About Plymouth" (jointly run by the City Museum and our own School of Biological Sciences at Plymouth University). The featured bug hunt took place in Plymouth's Ford Park Cemetery and featured a host of young and very enthusiastic entomologists sweeping through the cemetery collecting a large number of insects and spiders. The event was run by Andrew Whitehouse (from Buglife) and me.  It featured another wall-living spider, Amaurobius, which was teased from its lair with a tuning fork. The high frequency vibrations of the fork simulate the wingbeats of a flying insect trapped in the spider's web. This TV programme helped to show that cemeteries, when managed in the right way, can be gardens of remembrance and wildlife sanctuaries at the same time. It demonstrates the important role that such habitats can play in educating future generations about the beauty and complexity of the natural world.

Over the summer, I was also approached by the Society of Biology to help them develop an app for recording the distribution of house spiders across the UK.  This I did with the help of Geoff Oxford (President of the British Arachnological Association) and a series of excellent photographs from Stephen Falk  (Chief Entomologist at Buglife). Together we created an app that is now available for i-phone and Android systems. The app allows photographs and records to be sent into a central database where they will be mapped. This is an excellent example of citizen science and we hope it will generate an a large dataset that will provide an insight into the current distribution of the common spiders that can be found in our homes.

Spiders in and on houses have never been so popular, so download the app this autumn and see how many species of spider you are cohabiting with you. Then, if you are feeling bold, hunt over any old walls close by and see if the green-jawed Segestria is lurking in a hole in your neighborhood.