Latrodectus tredecimguttatus (Rossi, 1790), known as the Mediterranean widow, the Malmignatta or the European widow can also be called the thirteen-spots-widow because of the particular patterns found on the dorsal side of the abdomen of many individuals and often used to identify this species.
Actually this widow shows numerous colour variations to such an extend that the varieties have been formerly splited into distinct species [Walckenaer 1837]. Melanic and melanotic ones are often misidentified and other diagnosis tools have to be used.
According to Antonio Melic in his paper on the widows of the Iberian Peninsula, the female’s abdominal bifid setae of this species is a distinctive feature that separate it from other mediterranean and african species. Here are some pics below of the famous bifid setae.