(Images © Matjaž Kuntner)
Name: Caerostris darwini
Common Name: Darwin's bark spider
How it made the Top 10: This orb-weaving spider builds the largest orb-style webs that are known to science. Webs of this species have been found spanning rivers, streams and lakes with “bridgelines” reaching up to 25m in length and total web size reaching up to 2.8m2. The silk spun by these spiders has an average toughness of 250MJ/m3 with the highest measured at 520MJ/ m3. This makes it, “the toughest biological material ever studied, over ten times stronger than a similarly-sized piece of Kevlar” and more than two times stronger than any other known spider silk. The unusual behaviors of this new species will allow us to understand size dimorphism, mate guarding, and self castration (among others). Also discovered in association with Darwin's bark spider was an undescribed symbiotic fly species.
Reference: Kuntner, M. and I. Agnarsson. 2010. Web gigantism in Darwin's bark spider, a new species from Madagascar (Araneidae: Caerostris). The Journal of Arachnology 38(2):346-356.
Type Material: Holotype and paratypes – National Museum of Natural History (USNM), Smithsonian Institution, Washington D.C., USA.
Type Locality: Madagascar, Fianarantsoa Province, Ranomafana NP, Research station at Namorona River and surrounding forest, 21°15’S, 47°25’E.
Etymology: The species description was prepared on 24 November 2009, precisely the 150th anniversary of the publication of the first edition of Darwin’s book On the Origin of Species. The species is thus named in honor of Charles R. Darwin, 200 years after his birth.