INTRODUCTION

Spider silks show a remarkable range of mechanical properties (Madsen et al., 1999; Vollrath et al., 2001), with dragline silks in some species of orb web spider exhibiting elastomeric properties when wet and quite exceptional toughness either wet or dry (Gosline et al., 1986; Vollrath and Edmonds, 1989). The wide range of mechanical behaviour results from adapted design over an evolutionary time-span of circa 400 Mio years (Shear et al., 1989) in both the spinning solution (protein dope) and the spinning conditions (Vollrath and Knight, 2001). Recent studies are beginning to use sequence information of the spidroin dopes to reconstruct phylogenetic trees of silk sequence evolution (e.g., Gatesy et al., 2001). We have now begun a comparative study of silk gland evolution. And, if all goes well, the two trees should overlap, although both sides are still a long way away from this. For such a comparative study of spinneret evolution, the Brown Recluse spider Loxosceles sp. is of particular interest because, firstly, it is not closely related (Hormiga et al., 2000) to the orb-weaving spiders most studied for their silk and glands. And, secondly, its major silk is an extremely thin ribbon (Stern and Kullmann, 1975). The extrusion of a broad ribbon instead of a cylindrical thread suggested that the mechanism of formation must be different from that used to form the dragline threads in orb web spiders.