Small and successful

Long-jawed orb weavers: Pachygnatha degeeri

The name “orb weaver” has a poetic ring to it and the craftsmanship surrounding the design of an orb web is certainly deserving of such a title. The long-jawed orb weavers are known as the family tetragnathidae which are spiders that all spin a delicate web with a hole at the centre (hub). The only exception is the genus pachygnatha, members of which only spin webs as young spiderlings and these are never far from the ground. The older individuals eventually lead a ground-dwelling, web-less lifestyle (Foelix, 1996). Having said that adult spiders can often be found high up in vegetation during the night where they move about on numerous silk strands. Clearly species in this genus are very adaptable to different habitat strata.

Pachygnatha degeeri
By BKoe.

Pachygnatha degeeri is our most common species in the genus pachygnatha and also the smallest, about 2.5 – 4mm (Roberts, 1995). It can be found throughout Britain and northern Europe where it tends to inhabit low vegetation and grasses (Askins, 2013). The species has a dark carapace of rich brown but light hairless legs. The markings on the abdomen set each of the 3 British pachygnatha species apart.

P. degeeri along with a few other spider species appears to be a dominant pest predator on arable land in the north-west of Europe and has been described by many as an agrobiont because of its propensity to help control aphid and other pest numbers. They also appear to show preference for perennial habitats where plants mature over the course of at least two years. A study in Germany revealed that this species along with four others actually accounted for 56% of spiders within a crop field community (Schmidt and Tscharntke, 2005). Their impact on pest numbers and their ability to compete with other spider species over prey is still not definitive though, it could be down to population density or ecological niche but nonetheless this species is the most common member of the pachygnatha genus in the UK, and despite its size, remains a success across much of Europe too.

References

• Askins, M. (2013) Spider and Harvestman Recording Scheme Website: the national recording scheme for spiders and harvestman in Britain. Summary for Pachygnatha degeeri (Araneae).

Available at:

http://srs.britishspiders.org.uk/portal.php/p/Summary/s/Pachygnatha+degeeri

• Roberts, M.J. (1995) Colins Field Guide: Spiders of Britain & Northern Europe. HarperCollinsPublishers.
• Schmidt, M. H., and Tscharntke, T. (2005). The role of perennial habitats for Central European farmland spiders. Agriculture, ecosystems & environment, 105(1), 235-242.
• Foelix, R.F. (1996). Biology of spiders. 2^nd edition, Oxford University Press.