Strictly not for arachnophobes
Friday 15th January 2016
PETER FROST reports on the interminable and complex initiative to re-establish the ladybird spider – once thought extinct in Britain –in its natural habitat of a Dorset heathland
One of Britain’s rarest and most colourful spiders the Ladybird spider (Eresus sandaliatus) was thought to be extinct in Britain for over 70 years, until a tiny population was rediscovered on a tiny patch of land, barely 50 yards square, in Dorset in 1980.
Since then no other populations have been detected. It is believed to have once been found in Cornwall and the Isle of Wight but no more.
The spider gets its name from the bright red body of the male decorated with four large ladybird-like spots. The male body is 6-9 mm long excluding legs. The male’s legs are bright black with white stripes. The female is larger, 10-16 mm excluding legs and totally velvety black. She rarely leaves her nest. Young spiders too are velvety black.
The species lives in burrows with silk trip-wires covered with dense fluffy threads that radiate outwards to catch their prey, which includes large insects like devil’s coach horse and violet ground beetles.
The male only emerges for two weeks in May to breed. Having found a burrow containing a female he plucks at the trip wires in a way that distinguishes him from prey. This protects him from becoming a meal.
After mating, the female lays up to 80 eggs in a cocoon in her burrow during the summer and guards them until the spiderlings hatch in July or August.
She feeds them on regurgitated food and finally, rather ungratefully, the young spiders eat their own mother. Females only breed once.
The spiderlings disperse to make their own burrows in the following April, and take three or four years to reach breeding age.
The Ladybird spider is still so endangered in Britain that it has been possible to count each individual spider in Dorset, the only place it has managed to keep a small but determined eight-legged foothold.
The spider can only live on lowland heathland — and this is its main problem. Our native heathland has suffered drastic decline over the last century, being ploughed up for agriculture and forestry, or built over.
The Royal Society for the Protection of Birds (RSPB) reserve at Arne, just four miles from Wareham, Dorset, is a great place to see avocets and little egrets but it is just as important for its preservation of the native heathland in its original form and, of course, the Ladybird spider.
Arne boasts over 250 species of spider and hundreds of insect species including the threatened silver studded blue butterfly and the Purbeck mason wasp which is only found in Dorset.
As well as insects and spiders the heathland is also home to endangered reptiles such as smooth snakes and sand lizards, and rare birds such as the Dartford warbler, stonechat and nightjar.
The Ladybird spider’s long life-cycle, very specific requirements and the fact that it is not good at colonising new sites have all added to its vulnerability.
When it was first rediscovered in 1980, the last remaining site supported just seven individual spiders, but successful habitat management has resulted in the population expanding to its current level of nearly a thousand individuals.
Over the last five years other colonies have been established on Dorset heathland. Spiders have been carefully released onto new sites — increasing their populations in Dorset from one to eight. But there is still a lot of work to do.
For a start conservation charities like the RSPB want to establish at least 20 Ladybird spider populations in the wild.
If this spider is to thrive we need to continue the programme of releasing spiders onto new sites and to monitor existing populations to ensure that they are healthy and doing well. The habitat needs to be managed to ensure that the sites remain in the right condition for the spider.
In 2011, it was first released onto the RSPB’s Arne reserve. Surveys here carried out this year show that the spiders are doing well and are now expanding outside of the original release areas.
During the original translocation, scientists used an ingenious low-tech method of transferring the spiders. They used recycled empty plastic mineral water bottles which are an ideal shape and size for the spiders to make their nests in.
The bottles are filled with heather and moss and captured spiders from the donor site placed inside and monitored while they settled in and made a web. The bottles were then buried in holes in the ground offering some protection but allowing the spiders to venture out to colonise adjacent areas.
Toby Branston, RSPB Dorset reserve ecology manager told us: “It’s great to see this incredible little spider doing well in its new home. The hard work has started to pay off. Searches this year have found five new webs away from the release sites as well as others in their original bottle-homes. A great sign that the spiders are feeling settled here at Arne.”