Life colonises all environments, they say, but some habitats are more hospitable than others. Around our house, the swimming pool and its surrounding paving are actively hostile to small life – deliberately so, in a way, because we want to swim in clean water. We normally keep it salty and chlorinated, and the paving is bare, clean (-ish!) and dry. Nevertheless, life has found a niche – quite literally: there is a groove between the lip of the paving and the edge of the fibreglass which is a good little refuge for small-enough critters. Tiny skinks hide there, for instance, darting out to seize anything that lands on the paver above them.
A few days ago I saw a spider dart out to escape a wave I created. It looked at first glance like a young huntsman, which are common enough not to be very interesting, but no, it was too green and not quite the right shape. And a closer look revealed at least three of them spaced around the pool, with the occasional cast-off exoskeleton and little webs which may have been retreats or places for egg sacs
A bit of time online revealed that it was a Fishing Spider or Water Spider (Pisauridae), probably Dolomedes instabilis. They normally live on the edges of small ponds or slow-moving streams. Arachne.org notes that ‘some spiders in this family wait for prey at the water’s edge. Their front legs rest on the surface, sensing vibrations. They can grab tadpoles or fish swimming past, or race across the water to seize insects that fall in. Some Pisaurids form underwater retreats in large air bubbles, others make their webs in green leaves of shrubs.’
Mine won’t get very fat on underwater prey but should do well on small flies, etc, which fall in and drown. I have seen one resting on the pool side a centimetre under water, in a silvery air bubble, so perhaps it was waiting for live prey to touch down on the surface.
More pictures and information:
- Close-up (my photo on Flickr)
- Adult on paving (ditto)
- Brisbane Insects
- Find-a-Spider Guide