Can you recognise individual dragonflies from their faces?

bug-189906_1920Dragonflies are beautiful, alien-looking animals. They have bits that move and bend in ways that you wouldn’t expect, enormous eyes, and intricately patterned wings. I have written about the hydraulic gill system of dragonfly larvae, which powers both their jet propulsion and their “mask” that grabs prey. Meanwhile, dragonfly adults have basket-like legs to ensnare prey, as well as flexible abdomens which they use to form mating “hearts”. I’ve been interested in why dragonflies look the way they do, and that that means for their evolution, for a number of years.

I was intrigued, therefore, to read a paper that described how a pair of scientists had been able to tell dragonflies apart just by looking at the markings on their bodies. I do not remember how I first came across it, but the work is described in this German paper published in 2009 in the journal Entomo Helvetica by Schneider and Wildermuth*. The paper described a population of the southern hawker (Aeshna cyanea) in which a substantial number of animals could be identified from their facial markings. The paper is not creative commons so I can’t share the document, but you can see for yourself if you download the manuscript from the public link above and look at Figure 2 (it’s worth it – the pictures are stunning!). The title of the paper translates as “Dragonflies as individuals: the example of Aeshna cyanea“. So why might these markings occur?

There are lots of reasons why it might be advantageous for animals to be able to identify individuals. You might be trying to identify mates of high quality to increase your chances of reproduction. Many social animals (including humans, but also ants, meerkats, and molerats) distinguish relatives from non-relatives or friend from foe using sight or smell. Many theories of how cooperation evolved rely on animals having repeated interactions with one another, and remembering who has scratched whose back so that the favour can be repaid in the future. However, none of this applies to dragonflies. Dragonflies rarely have any structure to their mating (it’s usually first-come-first-served, and a mad scramble if many males are involved), they are not social (while they live in groups they do not necessarily act together), and they do not cooperate (apart from mobbing of predators such as hawks, but that’s probably not true cooperation).

A spandrel Photo by Maria Schnitzmeier, CC-BY-SA,

More likely what we are seeing is not the evolution of a trait, but the by-product of another trait. In a provocative article written in 1979, Stephen Jay Gould and Richard Lewontin wrote about this idea**: that some things we observe in nature are not the product of evolution directly, but occur as a result of some adaptation. Gould and Lewontin gave the example of “spandrels” from Rennaisance architecture. Spandrels (like the example on the right, from the Basilica de San Marco in Venice) were the accidental byproduct of the way that arches were designed – a small curved area was left in the corner of the arch, and this was often filled with artistic renderings. However, the spandrel itself was never the focus of the design.

In the case of dragonfly faces, the same is likely true. Dark patches on insects are usually caused by a substance called “melanin” (which is the same pigment that produces darker skin in humans). Melanin is involved when insects fight off infections or heal injuries. It is most likely that the patterns on the faces of the dragonflies are due to some kind of damage, perhaps during emergence from the water, or perhaps as a result of conflict between territorial individuals. What is most interesting, though, is that Schneider and Wildermuth seem to have found a population in Switzerland that has an unusually high number of animals with such markings. When I went to Flickr to look through other photographs of this species, I found very very few examples. Below is a gallery of some of the creative commons photos, and there are many more if you go to Flickr yourself and search for “aeshna cyanea”.

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That’s not to say there are no other examples. See here and here for examples of the markings in other photographs (but note that many of the most striking examples are taken by the same photographer).

Photo by Zak Mitchell.

The researchers who published the original paper offered an interesting addition to the literature on understanding individual insects. Usually, we do this by marking the animals (with dragonflies you can write on their wings, for instance, as you can see on the right) or more recently by attaching radio transmitters. There are some species that use natural markings to identify individual animals, including work on whales, dolphins, and killer whales. The technique is also used for some amphibians where the underside of the animals is often mottled in unique ways. However, given the fact that the markings are not always present, that we don’t know how long they last, and that the method requires some very specific (and challenging!) photography, it is unlikely that this particular method will be used widely in insect ecology. Instead, the study highlights an interesting example of unexplained variation in dragonflies, which deserves more study in its own right.


*Schneider, B. and Wildermuth, H. (2009) Libellen als Individuen – zum Beispiel Aeshna cyanea (Odonata: Aeshnidae), Entomo Helvetica, 2: 185-199.

*Gould, S.J. and Lewontin, R.C. (1979) The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme” Proc. Roy. Soc. London B, 205: 581–598

Community Collaborative Science (CoCoSci) as an alternative model for scientific collaboration?

G.Mannaerts, CC BY-SA 4.0,
G.Mannaerts, CC BY-SA 4.0,

I went to a fascinating talk by a colleague at Leeds, Dr Mark Davis, a few weeks ago. Mark works on Alternative Finance (“altfin”), which involves a shift in economic thinking away from traditional big banks (with low interest and risky investments) towards peer-to-peer and community-based lending. You can read more about Mark’s ideas in his recent Conversation article: “How alternative finance can offer a better banking future“. Mark had a lot of fascinating insights which (to a lay person like me) resonated strongly. The notion that banks are inherently risky and create the circumstances for economic collapse, and the idea that all of our money that we give to banks ends up going far away into large, complex economic systems, rather than helping closer to home. Mark also made the point that there is a parallel between the “Big Society” notion promoted by the UK Conservative Government under David Cameron, and the Alternative Finance concept that he promotes. Under the Big Society, it is assumed that everybody has a little bit of spare time here and there and that we can volunteer that time to solve social problems. This means lower investment from the government because we are (in theory) capable of taking over from public services. Some people are skeptical… Altfin, on the other hand, takes the same approach to capital: almost everybody has a small amount of capital sitting around that is doing nothing productive, and if we pool our spare capital then we can do good things with it. This got me wondering whether the same thing was true for research…

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Imposter syndrome and a note of thanks

A few weeks ago, I was honoured to have been given the Early Career Entomologist Award from the Royal Entomological Society and the Marsh Christian Trust. I’m not good at accepting praise and have always suffered from imposter syndrome. In the last year, I have done some relatively high profile events that have led to me speaking in front of hundreds of people. However, the thought of receiving an award in front of a few dozen of my peers terrified me. It is easy to sit in a lab or office all day, receiving scathing reviews of papers and grants (which are just par for the course, of course) and think that someone must have made a mistake when you finally achieve some degree of success.Read More »

To bee or not to bee – why some insects pretend to be dangerous

I just had my first article published at the Conversation – an excellent online collaboration between journalists and academics. As part of their publishing model, anybody can share any articles. So here’s mine!

To bee or not to bee – why some insects pretend to be dangerous

Christopher Hassall, University of Leeds

In the summer of 2011, panic gripped a small community in Gatineau, Quebec. Hundreds of small, striped insects were buzzing around a children’s playground. The playground was evacuated and entomologists were called in to establish whether or not the animals were dangerous. The answer was no, but it is easy to see why local residents were concerned. The animals that had taken up residence in the playground were hoverflies, a family of harmless fly species that have built up quite an arsenal of tricks to convince would-be predators that they are dangerous.

The panic that a swarm of hoverflies can generate belies the fact that they are immensely beneficial insects. Many of their larvae (the baby hoverflies that look like maggots) crawl around on plants feeding on the aphids that would otherwise eat our flowers and crops. Meanwhile the adults –- the stripy, flying insects that instil such terror –- spend their days pollinating flowers as they feed on nectar and pollen. But flying around in the open leaves hoverflies vulnerable to predators, a problem they have solved by evolving to resemble the stinging, pollinating insects such as bees and wasps with which they share the flowers.

Yet the story is not quite so simple. For every hoverfly that presents an exquisite example of mimicry (like the wonderful Spilomyia longicornis pictured above) there are several that really do not seem to be trying at all. Given that mimicry can obviously benefit hoverflies, why don’t they all evolve such excellent abilities?

Researchers found a potential solution to this Darwinian puzzle in 2012, when they looked into the characteristics of mimicking and non-mimicking hoverflies. You might expect that birds would prefer to eat larger species of hoverfly, since those hoverflies represent a bigger, more rewarding meal. Those larger species would therefore have more to gain from mimicry because they are under greater pressure from predators. Sure enough, it turns out that the colour patterns of the largest hoverflies (which are effectively flying buffets for birds) bear a close resemblance to the yellow, black, and white stripes of wasps and bees. The smallest species (which are barely worth chasing) do not show such similarity.

However, hoverflies have more than just wasp-like costumes. Some species also have considerable acting talents. It has been known for decades that certain hoverflies will pretend to sting when attacked, or hold their dark front legs in front of their heads to make it appear as though their antennae are long like those of wasps.

A recent extensive field survey showed that the species that behaved like wasps and bees were comparatively rare (just like the species that look like wasps and bees). This behavioural mimicry also tended to occur only in those species that already showed a strong visual resemblance to wasps and bees. In other words, those species that had the costumes also had the acting skills.

Insect sound bites

One of the most fascinating aspects of hoverfly mimicry has recently been dissected in great detail. As well as looking like wasps and bees, and acting like wasps and bees, some species also sound like wasps and bees. As part of our most recent project, my colleagues and I caught 172 insects from 13 species of hoverflies and nine species of wasps and bees, and brought them into a soundproofed recording studio. There, they recorded the sounds the insects made during regular flight and when the animal was attacked (simulated using a sharp poke with a pair of tweezers).

When they ran a statistical analysis on these sounds, the researchers found that some species of hoverfly make sounds when they are attacked that are indistinguishable from the high-pitched alarm buzz of bumble bees. The high-pitched buzz that bumble bees make seems to be produced by the bee unhooking its wings from the muscles that drive them, resulting in a completely different sound. This is a bit like what happens when you take your car out of gear and rev the engine – a lot of noise and you don’t go anywhere. It seems that hoverflies are capable of the same behaviour.

A board covered in ‘pastry prey’ used for experiments on wild bird predation.

But just because statistical analysis can’t tell the difference, that doesn’t mean natural predators can’t. To test for the benefits of this sound imitation in the wild, researchers presented pastry models of insects to wild birds with the different sounds. Pastry has approximately the same nutritional content as the insects that the birds forage on naturally, being part fat and part carbohydrate. The pastry can also be painstakingly painted to resemble insects as well, as in the photo to the right. To the surprise of the researchers, the birds only avoided the bee sounds. This was despite the fact that the hoverflies sounded identical to the computer-based analysis.

So we are left with a situation where an animal brain outperforms human researchers and their technical wizardry, which is not altogether surprising. Birds have evolved alongside a host of potential prey, developing the ability to find safe prey while avoiding animals that sting. While the hoverflies have a complex and fascinating suite of acting skills to dissuade would-be predators, they are still part of an evolutionary “arms race” where predators either keep up or starve.

The best part of this particular story is that it is possible to watch it unfold in your back garden. Next time you see or hear an animal that makes you reach instinctively for the rolled up newspaper, take a minute to check that it isn’t one of nature’s great actors.

The Conversation

Christopher Hassall, Lecturer in Animal Biology, University of Leeds

This article was originally published on The Conversation. Read the original article.

A hat-full of academic how-tos

Dipping in and out of the stream of tweets, there are always fascinating links to excellent resources for academics at all stages of their careers. I just spotted another, and thought it might be about time to aggregate some of these for posterity. Here’s the quick list (to which I will add if people suggest links), and details are below

  1. “How to find a postdoc”
  2. “How to get started with R”
  3. “How to use Github and RStudio”
  4. “How to use Github effectively”
  5. “How to respond to reviewers’ comments”
  6. “How to write a literature review”
  7. “How to help fight sexism in academia”
  8. “How to make your publications more accessible”
  9. “How to make your work reproducible”

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Messing about in boats

I realise that this is the second eulogy that I have posted on the blog in the last couple of months (which is all the more striking due to the low frequency of posts), but there was one passing recently that I simply have to mark. I was devastated to hear that Professor Brian Moss died recently. You will find a number of obituaries written by people who are better qualified to comment on his scientific work, and who knew him better as a person. However, while I was not as close to him as some, I did have the honour and privilege of learning from him as an undergraduate, a postgraduate, a postdoc, and as junior faculty, and so I feel the need to share some of the affection and deep respect that I felt for Brian. There have been a number of leading academics who have influenced my work and career (Dave and Tom in particular) and without them I would not have the collaborations, publications, or career that I enjoy today. However, I think it’s fair to say that Brian had the single largest personal influence over me from anyone within the academy, and shaped the academic that I have become. Other people watch David Attenborough on television, but I had the privilege of being taught by and working alongside my very own Attenborough who inspired me to think in different ways across disciplines. Read More »