Web-building in the social spiders depends on the availability of prey

Dr. Divya Uma’s interview with Bio Patrika hosting “Vigyaan Patrika”, a series of author interviews. Dr. Divya is a behavioral ecologist at the Azim Premji University (APU), Bangalore. She teaches undergraduate courses in biology. She is interested in concepts like predator-prey interactions, mimicry, sociality in insects and spiders. When she is not teaching, she likes to paint, listen to music and get lost in the forest! Here, she talks about her recent paper titled “Influence of prey availability on web-building in the social spider Stegodyphus sarasinorum (Araneae: Eresidae)” published in the Journal of Arachnology (2021).

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How would you explain your paper’s key results to the non-scientific community?

Spiders build their webs to catch prey such as bees, beetles, mosquitoes, moths, grasshoppers etc. It is known that spiders can manipulate the features of their web depending on the type of prey. Spiders can alter the spacing, thickness and stickiness of silk threads of a web. Social spiders can modify their web architecture depending on the amount of prey availability. If there is no prey available, then spiders incorporate a kind of silk known as cribellate silk that enables them to capture prey. If the spiders are full, then they do not invest less in this kind of silk.

Majority of the spiders are solitary—they live by themselves for most part of their lives. But only a few spiders are social. Among ~49,000 species of spiders, only about 25 of them are social. Why do they live in groups?—so that they can collectively hunt larger and numerous prey than their solitary cousins. They can also perhaps gain protection from predators. We study Stegodyphus sarasinorum, a social spider found in India.

Spider web closeup. Photo credits: Maitry Jani

We performed a simple experiment in the lab to examine if S. sarasinorum can alter its web architecture depending on prey availability. Saroja Ellendula, Carol Tresa – two undergraduate students carried out this experiment at the Azim Premji University. We got social spider colonies in Bangalore and gave them frames to build their webs. We then divided these colonies into two groups- the well-fed group that had an abundant supply of grasshoppers daily for a week, and the hungry group which did not get any supply of grasshoppers. We took photographs of their webs and found that the webs of the two groups are very different from each other. The unfed group had a lot more cribellate silk strands than the well-fed group. Unfed spiders put out cribellate silk to catch their prey and these silk strands were very evident. It is intriguing to know how spiders invest themselves in this very energetically expensive process of making the cribellate silk.

Web schematic with spiders

A bunch of spiders modifying their webs may sound trivial—but webs were once thought to be structures that could not be changed once they were built. Several recent studies have shown that webs are influenced by spiders’ own internal state (such as hunger, age of the spider) and external environment (prey availability, presence of predators, wind, rain). Here, we show that the social spiders can fine tune their webs according to the external environment such as prey availability.

What are the possible consequences of these findings for your research area?

We have shown that social spiders can modify their web architecture based on their internal needs. Social spiders are thought to cooperate in web-building, prey capture and taking care of their young ones. Whether individuals in a colony cooperate with each other or do they act as individuals driven by their own internal needs is something that needs to be examined. Our study was done in a controlled set up but we have to examine if this is really true in the field as well.

What was the exciting moment (eureka moment) during your research?

The cribellate silk that these spiders use to build their webs appear as zig zag lines and can be easily identified. We had set up this experiment in the summer in an empty classroom. It was so amazing to be able to accurately classify spider colonies either to the well-fed or the unfed group just by looking at their webs. I had no prior knowledge on the colony and their groups. The stark differences between the two groups were so evident to all three of us. Results are often not so clear cut like this and this really was an exciting moment.

What do you hope to do next?

Social spiders are so fascinating and there are so many aspects to explore about them. We are really interested in examining how spiders in a colony behave, if some are full and some are hungry? Do the spiders that invest more in web-building also catch more prey? Do spiders respond collectively for the benefit of the group or do they behave like individuals? We also want to see if cribellate silk generates different kinds of vibration than non-cribellate silk? How is the vibration carried through the web? I will be delving into these questions further with the help of my collaborators, Dr. Hema Somanathan from the Indian Institute of Science Education and Research Thiruvananthapuram, Dr.Tejas Murthy and Dr. Debraj Gosh from the Indian Institute of Science, Bangalore.

Where do you seek scientific inspiration?

I seek my scientific inspiration from nature, for sure! There are so many fascinating aspects of nature that we do not know. Additionally, interacting with people from different disciplines helps me to think about a topic from a different perspective. I teach at a liberal arts program at APU and here, I often end up chatting with economists, physicists, or historians. These conversations really help me to think out-of -the-box, and incorporate new ideas in our investigations.

How do you intend to help Indian science improve?

Science can be done only once you have a PhD or while you are pursuing a PhD is a false idea. If you are motivated enough at an undergraduate or a high school level, even these students can achieve a lot. Science is expensive and can be done only inside a laboratory is also a false belief. I try to create interest among students about the natural world around them. Once they are hooked, the rest follows! I also strongly believe that communicating scientific discoveries to the general public is important. Engaging common people through social media, podcasts, events where a layman gets to understand and visualize the kind of things scientists do is very crucial and I appreciate the efforts of Bio Patrika for working towards this goal.

Reference

Ellendula, S., Tresa, C., & Uma, D. (2021). Influence of prey availability on web-building in the social spider Stegodyphus sarasinorum (Araneae: Eresidae). The Journal of Arachnology, 49, 141 – 145.

Edited by: Neha Varshney

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