Underwater Spider

How do you feel about spiders? There are a lot of people who have arachnophobia. Personally, I find them to be both fascinating and creepy. Hopefully with today’s post I will increase your fascination of spiders by talking about the Eurasian diving bell spider, Argyroneta aquatica, which spends its life underwater.

A. aquatic have hydrophobic hairs on their abdomen and the ventral side of the cephalothorax which help the spider trap air at the surface of the water. They are also able to create an air-filled bubble, called a “diving bell”, by forming webs on underwater vegetation. This bell can act as a “physical gill” by taking up dissolved oxygen from the water (Seymour & Hetz, 2011).

  

Besides spending its life underwater the diving bell spider is different from other spiders because the males are larger than the females. In many species the females are larger than the males which mainly depend on variation in female size (Head, 1995). However, in A. aquatica males are larger than females and have a more elongated body. The first legs and chelicerae were also longer in males. These differences may benefit males because they are more mobile than females and longer legs help the spiders dive while in the water (Schütz & Taborsky, 2003). Different pressures may be influencing the two sexes and causing them to have different body conditions and shapes. If male spiders are more mobile than females predators may be a greater risk to the survival of the male spiders. This could result in natural selection occurring in which slower spiders will be preyed upon and spiders that are able to travel through the water faster will have a higher fitness.

Here's a short video of the diving bell spider underwater:

References:

Head, G 1995, ‘Selection on fecundity and variation in the degree of sexual size dimorphism among spider species (Class Araneae)’, Evolution, vol. 49, no. 4, pp. 776-781, doi:10.2307/2410330.

Schütz, D, & Taborsky, M 2003, ‘Adaptations to an aquatic life may be responsible for the reversed sexual size dimorphism in the water spider, Argyroneta aquatica’, Evolutionary Ecology Research, vol. 5, pp. 105-117, <http://www.evolutionary-ecology.com/issues/v05n01/kkar1477.pdf>.

Seymour, RS, & Hetz, SK 2011, ‘The diving bell and the spider: the physical gill of Argyroneta aquatica’, The Journal of Experimental Biology, vol. 214, pp. 2175-2181, doi:10.1242/jeb.056093.