The water spider Argyroneta aquatica is the only spider in the world that lives almost all of its life underwater. It is widespread in the UK but probably under recorded due to its aquatic habits. In July this year I was given the job of finding some of these spiders for Channel 5 to film for a new wildlife series. The best site locally for them is Exminster Marshes. I had last seen them here about ten years ago. So after gaining permission from the RSPB I visited the site to look for the spider again. After a fruitless four hour search I returned to almost the spot where I had began and found a spider in my pond net on the first dip! Out of water the spider looks quite ordinary being dark and velvety but put in a jar of water and its appearance is transformed. The hairs on its body trap air giving it a beautiful ‘quick silver’ appearance as it swims around.
I kept a few of the spiders in a tank and fed them on water lice. They constructed their diving bells amongst the pondweed by transporting air from the surface on their bodies and placing it under a web of silk. The spider then lives in the diving bell and only visits the surface to replenish its air supply. I watched a male swim to a females’ diving bell and mate with her several times. The female then spun a silk egg cocoon in the diving bell which was greatly extended. After a few weeks tiny silver bubbles around the diving bell revealed that the tiny spiderlings had emerged.