Increased number of observations and notes of offspring production in the invasive orb-web spider Argiope bruennichi (Scopoli, 1772) (Araneae; Araneidae) in Finland

Authors

• Juhani Terhivuo Finnish Museum of Natural History, University of Helsinki
• Niclas R. Fritzén
• Seppo Koponen University of Turku
• Timo Pajunen Finnish Museum of Natural History, University of Helsinki

Abstract

Prior to 2005, the orb-web spider Argiope bruennichi (Scopoli, 1772) was unknown in the Finnish spider fauna. In 2005–2010, four specimens in three localities were found by laymen. In 2011, 13 specimens were observed in various parts of southern Finland. The sample sites are separated by long distances suggesting that A .bruennichi specimens are spread by anemochory, i.e. by ballooning. All the individuals were females. Two cocoons (egg sacks) constructed by one of the two females reared in captivity and one cocoon constructed outdoors by another female yielded live offspring. Whether young A. bruennichi passed the winter in cocoons in Finland or arrived from abroad in spring 2011 prior to reaching maturity during summer of the same year is unknown. Here we compile the records of A. bruennichi gathered in Finland in 2005–2011. We document the arrival and reproduction of this alien spider at the northernmost edge of its range and discuss its dispersal in Northwest Europe and factors related to the establishment of permanent populations in general.