GROUND SPIDER - Drassodes cupreus

This inch-long spider was resting on the outside of the kitchen wall this morning - as fed up with this bloody rain as the rest of us (probably)?!

This is one of the ground spiders - from the Drassodes genus, and almost certainly Drassodes cupreus - a very "famous" spider, if you know your spiders that is.

It was in this species of spiders, in 1999, that 2 swedish chefs, sorry, scientists, discovered that at least this species of spider has an "in-built compass" to help it navigate.

Now, you might be forgiven for thinking here that most spiders have eight eyes and if you had eight eyes all around your head, you could probably navigate without the use of an inbuilt compass...?!

Possibly. Although I know some people who couldn't even tell me which way was north (or south) from their house, and they'd been living there over 30 years - (you know who you are)!

Anyway, Drassodes cupreus' "compass" is actually a secondary pair of (lens-less) eyes that sit just behind the spider's principal eyes on the cephalothorax (combined head and body).

These eyes are used not to form any image (no lens you see), but to analyse the precise direction of polarisation of the light in the sky, using a unique built-in filter.

Because the orientation of light in the sky changes according to the position of the sun, the eyes effectively provide bearings for navigation, working best at dusk and dawn - to help them navigate away from and back to their nests during hunting trips (these are hunting (ground) spiders after all).

OK. Right. So how on earth did these two Swedes work this out?

Answer - by giving the spiders navigation tests in a lab, and covering, yes, covering certain of their eyes up - with liiitttle teeensy weeensy spider blindfolds - I kid you not.

Yep. Your worst nightmare come true. Even if you cover the principal eyes of this spider up, it can still come and FIND YOU...! Mwah ah ah ah aaaahhhhh!!!

Since 1999, there has been some evidence of similar organs in other species of spiders, so the integral compass might not be limited to Drassodes cupreus after all, but it was the first spider, like I say, to have this discovered in.

Drassodes cupreus then, a hunting spider, a ground spider, (smooth-bellied), with built in sat-nav. The TomTom of the Spider world.