Social Spiders: Sharing is Caring

When we think of Huntsman spiders, we think of eight legs of pure Arachnid stalking the Australian bush land in solitude in search of their next meal. Dr. Linda Rayor of Cornell University is out to change this misconception: with a recent seminar at Macquarie University on the sociality of the Australian Huntsman Delena Cancerides.D. cancerides is one of only 85 of the 44,500 known spider species said to take part in a social lifestyle and like all Huntsman (Sparassidae: Deleninae) species, do not build webs for prey capture and in fact forage nocturnally1.

alan henderson

Delena Cancerides. A photo by Alan Henderson5

How do we define sociality in spiders? Firstly, we must remove ourselves from the preconceived notions of other known social insects such as bees and ants. Social spiders live in foraging societies as opposed to reproductive groups, common in other forms of social living2. These colonies are led by a single dominant female, not unlike many households today, and are responsible for the protection of not only the colony’s members but the retreat itself (the spiders home).Colonies generally consist of 1-4 cohorts of offspring, with a large variation of offspring instars (age) within each colony.

instar

Figure 2: Instars of Delena Cancerides1

D. cancerides exhibits social behavior through the act of prey sharing, where a percentage of prey caught by larger, more mature spiders is brought back to the retreat to be shared with the younger, immature spiders. The concept of sibling rivalry is almost entirely void in D. cancerides as this act is not only highly beneficial towards the younger spiders of the colony (increased weight); but incurs a completely negligent impact on the mature ‘sharing’ huntsmen1. The complexity of prey sharing in D. cancerides becomes even more unique when incidence of cannibalism in other species of spiders is taken into account3. Solitary spiders will often cannibalize other siblings or spiders they encounter in preference to prey sharing, tough love4? Dr. Rayor suggests a level of tolerance between siblings of the colony in D. cancerides, giving homage to the age old saying ‘sharing is caring’.

Making this colonial behavior a possibility is the spiders’ ability to recognize nest mates, generally thought to occur through chemical signaling, allowing the matriarchal spider to defend the colony from foreign colonial invaders whilst adequately protecting members of her own colony until they mature3. D. cancerides offspring will often remain in the retreat for 45 weeks before dispersing (at sexual maturation) from the colony in search of food and mates. This behavior not only mimics the life of the common teenager, but is also congruent with delayed mobility and feeding from birth in comparison to solitary huntsman4.

The spiders’ strict habitat also procures a strong area of interest in these social creatures; after all, home is where the food is. Rayor explains that retreats are often only a few centimeters deep and commonly found in the decaying remains of Acacia species6. D. cancerides often suffer from enormous pressures as a result habitat saturation, meaning the retreats available are at full occupancy. Rayor’s observations have shown that as available retreats become rarer, occupancy is increased leading to the potential ‘take-over’ of the retreat by a rival female. Retreats can often be ‘a ticking time bomb’ as decaying trees often have a limited window of occupancy before decomposition leads to its inhabitable. Once a retreat has completely degraded the inhabiting colony is lost as result6.

Dr Rayor’s work on D. cancerides has further shed light on the evolutionary advantage of a social lifestyle, where the benefits of sharing outweigh the costs. Studies such as this continue to advance out knowledge in the complexities of social interaction in arachnid species. D. Cancerides is not the only social huntsman studied by Rayor with D. lapidocola and D. melanochelis, also declared subsocial species. To learn more about sociality in Spiders and in particular the work by Linda Rayor on D. cancerides see the works below:

1Yip,E. & Rayor, L. 2013. The influence of siblings on body condition in a social spider: is prey sharing cooperation or competition? Animal Behaviour 85(6): 1161-1168.

2Whitehouse, M. E. A. & Lubin, Y. 2005. The functions of societies and the evolution of group living: spider societies as a test case. Biological Review 80, 347-361.

3 Yip, E. C., Clarke, S. & Rayor, L. S. 2009. Aliens among us: Nestmate recognition in the social huntsman spider, Delena cancerides. Insectes Sociaux 56, 223-231.

4 Yip, E.C. & Rayor, L. 2013. Maternal care and subsocial behavior in spiders, Biological Reviews, doi: 10.1111/brv.12060

5 Image: Henderson, A. Taken from: http://www.biodiversitysnapshots.net.au/bdrs-core/public/speciesInfo.htm?spid=282&mode=fieldguide

6Rowell, D. M. & Avilés, L. 1995. Sociality in a bark-dwelling huntsman spider from Australia, Delena cancerides Walckenaer (Araneae: Sparassidae). Insectes Sociaux, 42, 287-302.

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