The 'Black Widows' from Madagascar

Madagascar is an island known not to harbour poisonous species however it shelters black widows all generally called by the natives 'Menavodi' which means 'red ass' and which refers to the red hourglass mark located on the posteroventral part of the spiders. In his synthesis work on the araneids of La Réunion, Mauritius and Madagascar, Vinson (1863) informs two black widows on 'La Grande Isle': Latrodectus menavodi Vinson, 1863 and Latrodectus erebus Walkenaer, 1837 (made synonym of L. tredecimguttatus Rossi, 1790, later). Subsequently, two scientific publications indicated the presence of L. cinctus and L. obscurior (the latter also considered as a subspecies in the clade geometricus, i.e. Latrodectus geometricus obscurior) in addition to L. menavodi. Concerning species sampled in Madagascar, before the present work, only one DNA sequence coding for the cytochrome oxidase I existed, that of L. menavodi.

This work aimed to identify by DNA sequencing and to characterize morphologically specimens of latrodectes collected in the south of Madagascar near the village of Andranovory. Partial sequences of the 16S rDNA, 18S rDNA and COI genes were obtained. Phylogenetic analyses indicate that the sampled specimens fall into the 'geometricus' clade which is quite distinct from the 'mactans' clade, in which L. mactans menavodi is found. Morphological analyses identify the species as Latrodectus obscurior. The geometricus are invasive latrodectes for the first time formally identified in Madagascar. They form the group of brown widows. Madagascar, therefore, has at least two species of widows, the black widows 'menavodi' and the brown widows 'geometricus'. The two widows are feared for their bites which, at the very least, cause fevers and vomiting.