Stabilimentum

“I came across this Trashline Orb Spider (Cyclosa sp) and its delightful web on 31/12/2015 in my usual jungle habitat at Kledang-Sayong Forest Reserve, Ipoh, Perak, Malaysia. The spider creates a web decoration or “stabilimentum”. This is a silk structure that is very conspicuous and often built in the center of the web. The Cyclosa Orb-weaver spider are also known to decorate their web with other debris, like leaves and this is thought to help with camouflage but the purpose of the stabilimentum is unclear.

“There is much debate as to the purpose of this structure and design. The design must take time and the silk comes from protein molecules; both indicate the investment by the spider in the structure. Hence the structure and design are unlike for pure aesthetics. There are many theories regarding the function of the stabilimentum. Originally it was thought that it was to strengthen the web, reducing tension and frailty, hence the term stabilimentum. Some believe it is for either camouflage or makes the spider ‘look bigger’ hence offering protection. Other opinions are that it is to make the web visible so that birds and large flying creatures avoid it; hence saving time and energy re-building the web. Thermoregulation, stress, attracting prey or attracting a breeding partner and regulation of excess silk have also been proposed.

“One study by Blackledge & Wenzel supported the opinion that ‘stabilimentum building is a defensive behaviour’ or “web advertisement”. They showed that ‘webs without stabilimenta were damaged significantly more often than webs with stabilimenta’. However they also showed that the presence of the “stabilimenta reduce the prey capture success of spiders by almost 30%”.

“However a recent study has found the opposite. Kim, Kim & Choe found that ‘webs with the decorations caught twice as many large prey insects than unadorned webs’. Their study supports earlier idea that ‘spider silk is an excellent reflector of ultraviolet light’ and that the stabilimentum may function to lure prey. Prey attraction may be the primary reason for such intricate structures. The researchers have expressed caution and suggest that different Orb spiders may use the stabilimentum for different purpose and more work is required.

“Meanwhile we continue to enjoy the beauty of these creations.

References and More Reading:
1. Web decoration. Wikipedia. (https://en.wikipedia.org/wiki/Web_decoration)
2. Debbie Hadley. Why Spiders Decorate Their Webs (http://insects.about.com/od/spiders/tp/Why-Spiders-Decorate-Their-Webs.htm)
3. Ella Davies. Decorative spider webs attract dinner. BBC Nature. (http://www.bbc.co.uk/nature/19639387)
4. Todd A. Blackledge, John W. Wenzel. Do stabilimenta in orb webs attract prey or defend spiders? Behavioral Ecology (1999) 10 (4): 372-376. doi: 10.1093/beheco/10.4.372 (http://beheco.oxfordjournals.org/content/10/4/372.full)
5. Kil Won Kim, Kyeonghye Kim, Jae C. Choe. Functional values of stabilimenta in a wasp spider, Argiope bruennichi: support for the prey-attraction hypothesis. Behavioral Ecology and Sociobiology (2012), Vol 66, Issue 12, pp 1569-1576 (http://link.springer.com/article/10.1007%2Fs00265-012-1410-8)

Dato’ Dr Amar-Singh HSS
Ipoh, Perak, Malaysia
9th January 2016