Huntress in the House

I suspect that if I were rather smaller - the size of a silverfish say - I would find this a pretty terrifying prospect. I probably wouldn't be given much time to consider the matter however.

Female Huntsman Spider Isopeda villosa, on our bedroom wall.
I am grateful to Dr Linda S Rayor of Cornell University for identifying her for me, instantly and graciously,
and to Dr Dave Rowell of the Australian National University for forwarding my request to her.

The greatest initial threat to me, in my temporary guise as a silverfish, would be those eight long quick legs. Most spiders have two pairs facing forwards and two back, and walk fairly deliberately with the bodies held high. 

Orbweb Spider (possibly Eriophora transmarina, a very variable species) showing the leg configuration
of most spiders.

The huntsmen (in this case Family Sparassidae) have all four pairs bending backwards; perhaps counter-intuitively they run sideways however! Their body touches the ground as they run.

Another view of 'our' huntress. The splayed out legs can be seen clearly, along with the fact that each has seven joints.
The two joints closest to the body are short, but in huntsmen the outermost one, the tarsus (the 'foot') is unusually long. Overall this gives great agility.

The photos here were taken on a vertical wall, which she glides over as easily as if it were horizontal. Most spiders have three little claws on the tip of each tarsus - the outermost leg segment. In this magnified shot of the two rearmost tarsi, we can see that she has two such claws; what we can't really make out is that instead of the third claw she has a brush running the length of the underside of the tarsus to further help her grip the surface.

We can just see the two claws on each tarsus.

We can also clearly see the hairs which cover her legs (her name villosa means hairy). These are sensitive to vibrations, including those of air currents.

A closer view of the head wouldn't give me much confidence either, in my silverfish persona.

Eight eyes (four small ones above four large ones) would ensure I was clearly visible to her, were I a silverfish. The massive chelicerae (fangs), between two palps, are definitely all the better to eat me with. More below.

Unlike insects, with three body segments, spiders have just two; they have an abdomen like an insect, but a single cephalothorax includes head and 'chest', and carries the legs. The first pair of appendages on the cephalothorax are the massive chelicerae, seen here immediately below the four larger eyes. They comprise the large basal segments, which can be effective crushers, folded into which (out of sight) are hard sharp fangs, which inject venom via a tube. Her mouth parts are hidden behind them. Rapidly resuming my human persona, even if I were to harass her enough to make her bite me, the venom would do me no harm - it is mostly designed to break down insect bodies for easy digestion. The fangs would give me a painful - and fully deserved - stab though. 

Outside the chelicerae is a pair of six-jointed palps, resembling short legs (see pic above). They are sensory and are used to help manipulate food; in the male however they are swollen at the tip and are effectively sexual organs, carrying and transferring sperm.

These spiders are often referred to as tarantulas. The name it seems originated with the town of Taranto in Italy, which also gave its name to the dance Tarantella. The spider, which was actually a wolf spider of the family Lycosidae, was reputed to cause the dance by biting - or alternatively the dance was the antidote to the bite, it all depends on your choice of myth. It seems that the bite of the local wolf spider could in fact cause considerable distress, though there are diverging views on this. However this is the opinion of Bert Brunet in his excellent Silken Web; a natural history of Australian spiders, and I readily defer to him. Other opinions always welcomed however! 

Whatever the truth of that, the name became transferred to the primitive big hairy scary-looking (but generally harmless) ground-dwelling American spiders of the family Theraphosidae, though the family is found through much of the warmer world. How and why the name then transferred here, to yet another family of spiders, is unclear. 

Tarantulas; above Blanquillo Lodge Peru, below Sacha Lodge Ecuador

Whatever you choose to call her, our huntress is a very welcome member of our household. Tough luck silverfish!

Next time it's probably time to return to the long-promised discussion of red and black creatures.

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