Shichang Zhang: Spiders, detritus decorations and avoiding predators

Dr. Shichang Zhang of Hubei University discusses with us his team’s most recently accepted article, “Detritus decorations as the extended phenotype deflect avian predator attack in an orb-web spider”, his interest in the natural world, as well as his opinion on the best and worst parts about being an ecologist.

Shichang Zhang (credit: Luyao Chen)

About the paper

What is the background behind your paper?

Animals have evolved to use all kinds of strategies to deceive predators. One of the most commonly used strategies is predator deflection, such as tail autotomy in many geckos and eye spots in the wing of some butterflies. These behaviours or features can deflect the attack of predators away from their vulnerable body regions. Also, some animals actively attach exogenous materials to their bodies or their biogenic structures in order to get an effect of background matching or masquerade, so as to prevent recognition or detection by predators. By decorating themselves with “trash” materials, these animals can effectively deceive predators, thereby increasing their chances of survival. In arthropods, this strategy occurs in many diverse lineages, such as crabs, insects, and spiders. In spiders, it has been mainly reported in a few taxa, such as Cyclosa spiders.

There are two predominant function hypotheses in explaining the detritus decorations built by Cyclosa spiders: strengthening foraging success and defending against a predator. Detritus decorations may function to conceal the spiders from insect prey or predators through the mechanism of camouflage, thus increasing prey-capture success and preventing detection of predators. Alternatively, detritus decorations may divert the attacks of visually guided predators, such as avian predators, away from spiders.  However, there is limited empirical evidence to support it.

What’s your paper about?

The paper discusses the avian predator deflection function of the detritus decorations constructed by an orb-web spider, Cyclosa monticola. The spider spins vertical orb webs and constructs a linear detritus decoration to its web using silk, moults, prey remains, or plant detritus (e.g., leaf fragments and small stems). The decoration crosses the hub, with the spider facing downward and crouching in the hub during the day. We investigated whether detritus decorations constructed by the spider diverts the attacks of avian predators away from the spiders and towards their decorations in two ways. First, we studied whether domestic chicks and blue tits can discriminate between the colour of C. monticola and that of the decorations against natural habitat background and white background using visual modelling. Second, we experimentally tested the deflection hypothesis in the laboratory using naïve chicks as predators under the two backgrounds. We put the chicks in a cage containing a web either with (S+) or without (S-) a spider and either with (D+) or without (D-) detritus decoration (a total of four types of webs: S+D+, S+D-, S-D+, and S-D-), and we recorded the predation events that occurred, especially what the chicks firstly attacked.

The result of visual modelling showed that both chicks and blue tits could not differentiate the colour of the spiders and that of their detritus decorations with both backgrounds. The predation experiments showed that with both backgrounds, chicks attacked the spiders much less frequently when their decorations were present on the webs than when their decorations were absent, resulting in greater spider survival advantage. Also, we found that the decorations were more likely to be attacked than spiders, regardless of the ratio of surface area of decorations to spider bodies when both spiders and decorations were presented. Therefore, our results support a deflection, rather than concealment hypothesis for web decorations.  

How did you come up with the idea for it?

I have many years of experience in studying functions of spider body colouration, and this study is a continued work based on those of my previous. The idea of using chicks as models to represent avian predators was inspired by literature, especially Skelhorn et al., 2010 and Skelhorn & Ruxton, 2010

What are the key messages of your article?

The detritus decorations constructed by the C. monticola spider can well protect the spider from the attacks of avian predators. It realized through diverting attacks of predators away from spiders and towards the decorations, rather than an effect of camouflage.

How is your paper new or different from other work in this area?

To our knowledge, this is the first study to empirically test the avian predator deflection hypothesis of detritus decorations of spiders. Generally, web-building spiders mainly have two types of predators, hymenopteran wasps and insectivorous birds. Using video recording in the field, Chou et al. (2005) showed that in another Cyclosa spider species C. confusa, detritus decorations deflected attacks by paper wasp (Vespa affinis) away from spiders and towards the decorations. However, it is unknown whether the detritus decorations can also deflect attacks of avian predators, which have great influence on the population of the spiders. 

Who should read your paper (people that work in a particular field, policy makers, etc.)?

People who are interested in animal behaviours such as camouflage, masquerading, mimicry and crypsis, and those who are interested in predator avoidance strategies of animals.

About the Author

How did you get involved in ecology?

I was born in a mountainous village, and I have been fascinated by all kinds of animals in nature since I was a kid. During my undergraduate stage, I chose entomology as my major, and several years later I obtained a master’s degree in entomology (research field was insect physiology). In the last year of my master stage, I attended a talk given by my later Ph.D. advisor Dr. Daiqin Li (a co-author of this paper), I was attracted to behavioural ecology, and was determined to follow him to study evolutionary ecology and behavioural ecology. He is an excellent advisor and behavioural ecologist, whom I always learnt from.

What are you currently working on?

I am working on body colouration of spiders.

What’s your current position?

I am an associate professor at Hubei University in China.

What is the best thing about being an ecologist?

I think the best thing about being an ecologist is that I have a lot of time to explore the nature, and there are so many things we have not figured out yet. Therefore, once I found something new, it is probably that I am the first one in the world to report it, and I think this is the main motive that is stimulating me to keep exploring nature. I really enjoy it.

What is the worst thing about being an ecologist?

The worst thing is I am always misunderstood by some people who are not studying science. When I was collecting spiders in the field, or when I was performing an experiment in the field, I always met some people that asked me what I was doing. When I told them, most of them would look at me like I am a freak. They asked strange questions such as: Are you seriously looking for spiders, so terrible!  Do you collect the spiders to eat? Don’t you afraid to be bit by spiders and then die? If you were bit by spiders, will you become a spiderman, shooting silk from fingers? Oh, now that I know what an ecologist is doing, I will tell my grandson to avoid this major, definitely!

Kid: Mommy, what are they doing? Mom: They are collecting rubbish, if you do not study hard at school, you will do the same thing when you grew up.

Read “Detritus decorations as the extended phenotype deflect avian predator attack in an orb-web spider in full here.

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