ECOLOGY AND ETHOLOGY OF THE MEDITERRANEAN BLACK WIDOW SPIDER Summer School of Science 2010 July 30 th - August 6 th Anton Perkov, Gimnazija Pula (Croatia) Sabina Ranogajec, Prva Gimnazija Varaždin (Croatia) Petra Korlević, University of Zagreb (Croatia) INTRODUCTION The Mediterranean black widow spider (Latrodectus tredecimgutatus Rossi) is commonly found across the Croatian coast. In Istria their ecology and venom were studied by dr. Zvonimir Maretić from Pula, who discovered that black widow antiserum could be derived from rabbits’ blood after they were bitten by a black widow. The cure had a commercial success. The male and female spiders have the same venom structure and the same type of red- orange spots with white borders, but the females are substantially larger than males (extreme sexual dimorphism) (Image 1). The myth about female black widow spiders eating their mating partners, even though correct for some other black widow spider species, is not scientifically proven for Latrodectus tredecimgutattus. One other characteristic of black widow spiders and their family Theridiidae, is that, unlike commonly recognized symmetrical spider webs, they build so-called cobwebs, recognizable at first glance as a tangled mass of randomly placed threads, making them stronger than other spiders’ webs. In the year 2002 there was a project about black widow spiders on the Summer School of Science in Višnjan. The team was called Arachne team, and their goal was to write down as many spider species living on the Istrian peninsula as possible. What they found was an invasion of black widow spiders, so part of the project was later focused on determining their distribution on the peninsula and on comparing the feeding habits between various locations. Image 1 A female (left) and male (right) black widow spider. We photographed these specimens on the parking lot near Dvigrad. The sizes are not scaled (the male appears larger in proportion to the female). The goals of our group (known also as the Arachne team 2.0) were first to research the locations, population numbers and feeding habits of black widow spiders on the Istrian peninsula, comparing them with the data from 2002, and second to make an ethology (behavioral) experiment in order to observe potential differences in their cobweb building strategies. Thus our project was divided between ecology work on the field and ethology work in our laboratory.