The social spider Parawixia bistriata (Rengger, 1836) (Araneidae) as a potentially significant source of avian mortality in the Paraguayan Chaco

Five cases of bird entrapment in the social webs of Parawixia bistriata (Araneidae: Araneinae: Araneini) are reported from the Paraguayan Chaco. These are the first reports of avian entrapment for this species, and add one new family (Thraupidae) and four new species to the global biological inventory of bird species caught in spider webs. The wing chord and masses of the largest two species, Tyrannus melancholicus (Tyrannidae) and Columbina picui (Columbidae) greatly exceed the maximum reported for other Neotropical species. It is argued that possibility of mortality from entrapment is not merely a matter of morphometry as has been previously suggested, but includes other factors such as spider species, silk type, and area of entanglement. A possible temporal relationship between the growth and life history of this spider and the potential for entrapment is postulated. It is proposed that increased deforestation in the Paraguayan Chaco could lead to an increase in avian entrapment in this webs of this species.