You’d think that arachnids and water was an unhappy combination, but one species of European spider has made boggy ponds their home.
The raft spider (Dolomedes fimbriatus) is the UK’s largest native spider – its body growing up to 2cm long.
It uses the water’s surface like other spiders use their webs – feeling for the vibrations of potential prey with front legs extended. Using this technique it hunts tadpoles, insects and occasionally small fish:
When alarmed, the water repellent hairs on the raft spider’s legs enable it to dive beneath the water, trapping a bubble of air to keep it alive until the coast is clear and it cautiously re-emerges:
The wetland pools favoured by raft spiders are increasingly rare in this country. On the RSPB’s Arne reserve in Dorset their habitat is lovingly preserved, and offers wildlife watchers easy access from the nearby heathland trail:
On a good day dozens of raft spiders at various stages in their life cycle can be witnessed at the pond’s edge.
The female raft spider is often considerably larger than the male and mating is a dangerous business. He approaches her cautiously, waving his front legs tentatively to judge her receptiveness:
She may rush out to scare him off on numerous occasions, after which she retreats and the process begins again, the male edging closer all the while. It’s a nerve jangling thing to watch, let alone participate in.
The female spins a silk bag to contain the fertilised eggs, which she carries about beneath her body, keeping it just warm and moist enough to ensure their survival:
Then, when the baby spiders are ready to hatch, she lashes the egg sac to vegetation at the edge of the pond and the tiny hatchlings emerge:
Mum typically lies in wait nearby to ensure that her young ones don’t come to any harm:
This phenomenon of hundreds of spiderlings crowded together for their own mutual safety is only really appreciated up close:
But soon the young raft spiders are large enough to fend for themselves and disperse around the pond.
Raft spiders are not fussy eaters. When times are tough and food is scarce, or when too many raft spiders compete for the same local resources, they may even turn to cannibalism:
Not such a pretty sight!