Study reveals strategy behind spiders' web etiquette

Jun 18, 2013 by Maggie Clune
Study reveals strategy behind spiders’ web etiquette
Orb web spiders emerging from their bivouac along silk threads, at nightfall. Credit: Francis Ratnieks

(Phys.org) —A species of spider that, unusually, lives in a colony but hunts alone at night is the subject of a new study by an international team of scientists including University of Sussex biologists.

Spiders are normally ferocious lone hunters and trappers of prey – even can end up as dinner for some species.

But in the case of the colonial orb-web spider Parawixia bistriata, individual survival is best served by co-operating and even tolerating a little bit of freeloading behaviour from colony-mates.

The researchers' observations are published in the July edition of the journal The American Naturalist.

Sussex academics Professor Jonathan Bacon, Professor Francis Ratnieks and Dr Margaret Couvillon took part in the field study in southern Brazil alongside scientists from the University of York and from Belgium, Brazil and Poland.

During the day the spiders (each about 4cm across including the legs) doze quietly together in a bivouac, a soccer-ball-sized huddle of hundreds of spiders in a bush or tree. The bivouac sits at the centre of a network of permanent thick silk lines which radiate out to adjacent trees and bushes.

Things change dramatically at sunset. The spiders move out along the silk lines and build many adjacent orb webs, one per spider, each anchored to several of the permanent silk lines. Before daybreak, each spider consumes its own web and returns, along the permanent silk lines, to the safety of the bivouac.

Early in the evening, when there is still plenty of web-building space, a spider already building its web or sitting in the centre of a recently-completed web bounce up and down at any spider walking on one of the nearby anchoring lines. Invariably, the intruder moves off, looking for a vacant space of its own within the network of permanent silk lines.

Study reveals strategy behind spiders’ web etiquette
A pair of colonial orb web spiders passing each other, without aggression on a thick silk line. Credit: Francis Ratnieks

However, things change once all the potential web-building sites become occupied. Bouncing is now rare as most or all of the spiders have a web. But if there are a lot of spiders, some may not find a vacant space. These webless spiders now ignore a resident's bounces and sit patiently at the web perimeter; they are occasionally rewarded by sneaking in to share a large insect prey with the resident.

Professor Bacon says: "Charles Darwin almost certainly observed this species while travelling overland in Argentina in October 1832, describing them in his Voyage of the Beagle as 'many large black spiders, with ruby-coloured marks on their backs, having gregarious habits'.

"Darwin went on to remark that 'this gregarious habit, in so typical a genus as Epeira, among insects, which are so bloodthirsty and solitary that even the two sexes attack each other, is a very singular fact."

Almost two centuries later, says Professor Bacon, scientists now understand that the spiders' behavioural strategies keep the peace and prevent these dangerous well-armed carnivores from getting into costly confrontations with their neighbours. "One night's food is not worth risking death for," says Professor Bacon.

Professor Ratnieks says: "This switch in the behavioral strategy of the webless spiders makes perfect sense. Early in the evening all respect the resident's ownership because there is a high chance of finding another web-building site. Later on, when there is little chance of finding a web-building site, it is better to ignore the bouncing and hang around an existing rather than search. But they never fight; this is simply too dangerous."

Explore further: Bees able to spot which flowers offer best rewards before landing

More information: Wenseleers, T. and Bacon, J. Bourgeois behavior and freeloading in the colonial orb-web spider Parawixia bistriata (Araneae, Araneidae), The American Naturalist, no. 182. www.jstor.org/stable/full/10.1086/670525

Related Stories

Male black widows look for well-fed mates

Jul 07, 2011

(PhysOrg.com) -- According to a new study published in Animal Behaviour, a male black widow spider is able to identify a female spider that has eaten well by simply taking a few steps on the web she spins. ...

Captured in silken netting and sticky hairs

May 16, 2013

The great ecological success of spiders is often substantiated by the evolution of silk and webs. Biologists of the Kiel University and the University of Bern now found an alternative adaptation to hunting ...

Why spiders do not stick to their own sticky web sites

Mar 01, 2012

Researchers at the Smithsonian Tropical Research Institute and University of Costa Rica asked why spiders do not stick to their own sticky webs. Repeating old, widely quoted but poorly documented studies with ...

Scientists crack the spiders' web code

May 31, 2011

(PhysOrg.com) -- Decorative white silk crosses are an ingenious tactic used by orb-weaving spiders to protect their webs from damage, a new study from the University of Melbourne has revealed.

Recommended for you

Why do snakes flick their tongues?

1 hour ago

Many people think a snake's forked tongue is creepy. Every so often, the snake waves it around rapidly, then retracts it. Theories explaining the forked tongues of snakes have been around for thousands of ...

User comments : 0