I’m not sure quite where the last six weeks have gone. I guess time flies during the first year at university! This weeks species is a truly amazing spider, the Water Spider, Argyroneta aquatica, also known as the Diving Bell Spider. I found my first just yesterday (08/10/2016).
The Water Spider is the 57th species of spider that I’ve found in the UK, and it’s got to be my favourite so far! Here’s a photo taken by my friend Toby Cotton, who I was helping to sample the diversity of aquatic life in our local reservoirs. Thanks for inviting me along, and taking such a great picture!
As you may be able to tell, this spider is underwater! Hydrophobic hairs on the abdomen allow a bubble of air to be carried round with the spider, so it can spend a long time hunting without surfacing, or returning to its ‘diving bell’. The diving bell is a much larger store of air, created by the spider amongst rooted underwater vegetation. The spider returns to its diving bell to feed, lay eggs, mate, overwinter, and top up its mobile air supply. The Water Spider is also adapted to its underwater lifestyle by having numerous long hairs on its back two pairs of legs. This allows it to swim powerfully enough to offset the buoyancy of its mobile air supply. The spider pictured above had grasped a small piece of leaf in the bottom of our bucket, and accidentally floated it up to the surface! A short while after the photo, the spider dived back down again, and grabbed a more substantial piece of plant matter.
The Water Spider actively hunts aquatic invertebrates, such as insect larvae and water fleas (Daphnia). I feel as though it must also take larger prey, as it can be 20mm in length, and has chelicerae strong enough to pierce human skin, delivering a fairly painful bite. I’m fairly fortunate that I was unharmed that day, as I was handling both the Water Spider, and loads of Saucer Bugs (large aquatic bugs that can stab you with their mouthparts if annoyed)! See photo below, showing curved front legs for grabbing prey.
A.aquatica is fairly widespread in the UK, but quite localised. It requires areas of water that are sheltered, and have very little if any flow. Here’s its distribution map (it looks like this was a new 10km square record, in Penryn!). It seems to be highly localised in Devon and Cornwall, so I’m very proud to have found it!
I hope this has been an enjoyable blog, and I hope people go out and find some local Water Spiders. They’re great!