From the pages of 'The British Tarantula Society Journal'
WHY? Urticating Hairs
by Jon-Paul Lamouroux
This hypothesis arose from a number of observations, as most ideas do. My observations were of a female Lasiodora parahybana who, when disturbed, would put her carapace into the entrance of her burrow (and only her carapace) and begin to kick hairs upwards towards my face.
Question: if she is in danger, why not descend down to the bottom of her burrow out of harms' way? By remaining at the surface with her soft, vulnerable abdomen exposed, she is putting herself at risk! Descending down to the safety of her burrow would surely give her greater protection. Why waste the precious resource of urticating hairs that can only be renewed once a year with the next moult.
A series of experiments showed that when threatened the sequence of behaviour was as follows: run to burrow; take up entrance stance; flick hairs; descend to base of burrow.
encouragement was found to be a damp wad of cotton wool (predator's nose!). I carried out these experiments wliilst acting as adviser to a film crew. One job was to prepare a film set enabling the camera man to film a Theraphosid flicking hairs. The question again is, why not go straight down the burrow out of harms way? Why risk presenting the spiders' vulnerable abdomen to the predator's face and canine teeth?
1 carried out another experiment in extending this sequence of behaviour further. 1 came up with the following: spider does not pause at the entrance but descends rapidly to the base of its burrow. If her pursuer is a predator capable of digging for food, it will immediately dig the spider out. Our unfortunate spider has no where to go; it is an easy meal.
If, on the other hand, the spider adopts the sequence observed above, the predator will be disabled by urticating hairs in its eyes and nose and be more concerned with ridding itself of its discomfort and forget about digging out the spider. Secondly, this is a possible learning curve for the predator (don't approach such a spider) and a survival line of adaptation for the spider. It could be said that the presence of these specialized hairs are proof that this adaptation works, or at least for some New World Theraphosids it does.
The hairs themselves are equipped with barbs which prevent their easy removal once embedded in the predators' pores. Each hair has a specialized base which allows its quick detachment to enable it to be thrown into the face of its pursuer.
From any theory many other questions arise. What behaviour follows when all the hairs are used up? Can a spider go into moult at will? Then what about the mechanical wear of these hairs simply by moving up and down the burrow? One can always tell a wild spider by the wear to the setae on the outer edges of the legs. This question could be answered by the observation that most spiders with urticating hairs also sport guard hairs on the abdomen. Few such guard hairs occur on spiders without urticating hairs, for example, Baboon and Earth-tiger type Theraphosids. Any thoughts?
© Copyright 'The British Tarantula Society', 1999-2007