PhD students do the weirdest things

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Me on fieldwork

PhD students do the weirdest things

Category : PhD Life

Lately, I have had some very peculiar reactions when explaining the current chapter of my PhD that I am working on. Maybe I’m not explaining it perfectly, or most eloquently, but these reactions include: staring; bemusement and confusion; and outright laughing-in-my-face, before asking me, “so this is your… job?” Some friends of mine have taken to calling me up on a weekly basis, putting me on speaker phone to their office colleagues, and asking me questions about what sort of work I have encountered that week- just to prove that I have a strange occupation. So I decided to start documenting the types of things I have found myself doing recently, in case other non-science folk out there fancied a laugh at what crazy scientists do in their day-to-day lives.

I’m writing this on a train, Cambridge bound, for a meeting to discuss – with a group of like-minded scientists – the ways in which we can use model caterpillars (that is, caterpillars made out of either pastry or plasticine) to answer some serious biological and ecological questions. Dr. Hannah Rowland and her behavioural ecology and evoultion research group, at Cambridge University, have a lot of experience using pastry caterpillars to mimic cryptic (different ways of camouflaging oneself) or aposymetric (brightly coloured warning signals to deter predators) prey to find out how birds react and learn about how to avoid them. There is also a website bringing together researchers using dummy caterpillars together, called “The Global Dummy Caterpillar Project”. So in the world of ecology and evolutionary research, dummy caterpillars are pretty well known.


A Canadian tiger swallowtail caterpillar mimicking a snake to avoid being eaten.

A Canadian tiger swallowtail caterpillar mimicking a snake to avoid being eaten.

The original source of the image above can be found in this article.

However, even in the science world, the use of dummy caterpillars is still quite strange and peculiar to some. Within diverse research departments, such as the Institute of Zoology at ZSL, methods used widely by one group can be alien to another. So to explain in broad terms, the use of dummy caterpillars in science is considered when one wants to ask questions about either i) the caterpillar (the prey) and their defence strategies against predation or ii) the predator – which predators are the main ones eating that prey? Other questions may come off the back of these, such as calculating predation rates from predators to be able to compare the rate of caterpillar predation in one area compared to another. Other evolutionary questions might be: “will novel patterns of brightly coloured prey be predated on as much as known patterns of brightly coloured prey?” Or “what are the main predators eating prey A?”. But mostly the question is either about the prey or predator.

That question about what types of predators are eating the dummy prey, is quite interesting. A few papers have used plasticine as their proxy prey so that when a predator bites into it, it leaves an attack mark or indent- uniquely shaped to that taxa (ie. birds, insects, mammals). A few studies have used this in their research to discover that a certain predator is more beneficial at reducing a certain prey than others, including this recent paper on determining which types of predator were the best at reducing crop pests in Ethiopia.

These are all very interesting questions and the answers can be interesting too, but what is the point? I can’t answer for other people in finding the value or meaning of their research. But I can start with explaining how the answers I get from my research can be applied in the “real world”.

This dummy caterpillar experiment acts as a specific question as part of my PhD.  The wider question of my work is “Does biodiversity increase the pest control ecosystem service on apple orchards?” The dummy caterpillars experiment will hopefully find out whether the orchards with higher biodiversity have higher caterpillar predation rates from birds. These sorts of questions can build a picture about farmland ecosystem services, such as pollination and pest control. If we can discover that farms with high biodiversity levels have a higher proportion of their pesky pest caterpillars (e.g the codling moth– a major orchard pest) eaten by the orchard’s resident birds, then we could suggest that birds are a key “pest control” ecosystem service. Farmers could potentially nurture this service and increase the prospect of needing to use less insecticides in the future, which are expensive and increasingly under scrutiny. Research is constantly used to ensure chemical usage on farmland is not debilitating the natural wildlife and is safe to be used around people. Therefore, bans are quite common for certain chemical pesticides, and the most recent ban is a well known and used insecticide – chlopyrifos, as discussed in this Farmers Weekly article. But birds are not going to be banned, as much I know anyway, so if a free pest control service can be provided by them, farmers may feel a bit more secure about their management regimes – as long as they eat enough caterpillars, that is. And this is what I am trying to find out.

I have just commenced this part of the study, which started mid April due to a very cold start to this spring. But before I started I needed to do a bit of pastry rolling and plasticine purchasing to work out which model caterpillar will be best for my study. To test both these prodigies (pastry v’s plasticine) I have been working alongside Dr. Hannah Rowland in Cambridge, where a newly built aviary allowed me to test my little plasticine caterpillars on four little blue tits*, to see what types of marks they will leave in the plasticine models. I was also able to test to see if there was a colour preference between green or cream, or if the blue tits started to learn that what I was presenting them with was not food, no matter what the colour.

Contemplating whether to try the dummy caterpillar below

Contemplating whether to try the dummy caterpillar below

After randomly presenting all the blue tits with either a green or cream model caterpillar, I found that there was no colour preference and that some blue tits are just a bit more clued up than others! Some clever little birds would only peck one colour once, but other would keep trying newly presented dummies of the same colour. But overall, they all tried each colour once. So from this mini experiment I have decided to use both green and cream in my experiments in the orchards!

A perfect peck mark left by a blue tit

A perfect peck mark left by a blue tit

So that’s it on the planning phase, next up will be more pictures like this one of me checking some dummy caterpillars in a lovely little orchard. I might even pop in some camera trap pictures of what has been attracted to these dummy caterpillars so far.

I hope I leave you with a little less baffled facial expression to when you first read the words “pastry” or “plasticine” and “caterpillars” in the same sentence. Research must definitely be up in the top 10 most peculiar jobs, but that’s what makes it fun!

Charlotte Selvey


* These four blue tits were humanely kept in this experimental aviary for 2 nights before being released back in the wild. Cambridge University had the correct licenses for their research on blue tits to take place.

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