Who’s that fly and WHAT is it eating? A new paper from the lab

One of the most widely used products of taxonomy is the identification key. A key allows somebody who isn’t a specialist on a particular group to put a name on an unknown species. At least, that’s how it all works in Dream World. Unfortunately, as a frequently used cliché in taxonomy says: many keys are written by people who don’t need them, for people who can’t use them. In other words, the expert who wrote the key knows exactly what he or she means by “wide” vs. “narrow”, or “normal” vs. “pale”, or “modified” vs. “unmodified” (and they haven’t bothered to include any pictures), but that’s no help at all to the student sitting at a microscope 500 miles away and 50 years later, who has never talked to that expert.

We (taxonomists) should be writing keys that are used and usable by people who are not taxonomists, thereby letting us (taxonomists) get on with the enormous task of describing all those new species that aren’t yet in the keys. But a lot of keys aren’t usable. I’m a fly taxonomist and even I can’t work my way through some fly keys, because they’re, well, awful.

We must, as my colleague and mentor Steve Marshall puts it, democratize taxonomy. A few years ago, Steve made a major contribution to the democratization of taxonomy when he launched the Canadian Journal of Arthropod Identification, an open-access, online journal with the express mandate of making identification easier, especially for non-specialists.

Forensic entomologists are one group of non-taxonomists whose work depends on accurate identification of insects. And it’s a lot harder to identify those insects than TV shows would have us believe. One of the main groups of forensically important insects is the blow flies, family Calliphoridae, and there’s a CJAI key for that. But many other insects are part of the carrion community, including a group of little flies that often comes later to the party, colonizing bodies in more advanced stages of decay. This is the family Piophilidae, and they’re small and hard to identify. And because of that, many forensic studies either don’t identify them, or get them wrong. That’s a problem because those studies are potentially missing out on important data. Fortunately for forensic entomology, we now have a North American expert on this family — Sabrina Rochefort, a M.Sc. student in my lab.

Sabrina has just published her first journal paper, along with collaborators Marjolaine Giroux, Jade Savage and me. Sabrina decided to address the lack of a decent key to the piophilid flies for forensic entomology. Her paper, just published in CJAI, is the first well-illustrated key to the species of piophilid flies associated with dead bodies in North America.

Mycetaulus subdolus. A piophilid fly. It eats dead things.

Mycetaulus subdolus. It eats dead things.

Sabrina’s first task was determine which piophilid species are important in forensic entomology and which species tend to eat fungi, decaying vegetation or other things (it’s an ecologically diverse family). A review of the literature helped start building the list, but examination of label data on specimens in museum collections turned up some new records of piophilid species on carrion as well. A third great source of data was an ongoing field study led by our co-authors Marjolaine and Jade on insects associated with carrion in three different regions of Quebec. This combination of fieldwork, museum material, and published records is often how we find and compile taxonomic and ecological data.

The next, and most important, step in building a key is to decide which characters are the most useful in distinguishing species, but also the most easily visible and least ambiguous. There might, for example, be obvious differences in small parts of the male reproductive system, only visible after you dissect specimens. Or it might just be easier to see if the legs are yellow or black. Ideally, a key should be clear to somebody who’s never looked at these insects before. And the easiest way to accomplish that is with illustrations. Good illustrations. Lots of them. With arrows and circles showing important things. And clear language in the key that links to those pictures.

The easiest way to make a key. Does it look like A or does it look like B

The easiest way to make a key. Does it look like A or does it look like B?

Once a species is identified, it’s also very helpful to know a little more about it, so the paper also includes a species page for each piophilid, listing what’s known about its habits, geographic distribution, and any known variation in colour or shape. This sort of natural history information isn’t always included in published keys, but it’s very helpful for people (like, say, forensic entomologists) wanting to know a little more about the fly they’ve just identified.

A species page from Rochefort et al. (2015)

A species page from Rochefort et al. (2015)

Of course, these forensically relevant species are only a small subset of the piophilid flies we can find in North America. They live in a range of habitats, from the arid southwest, to the highest high arctic islands, and they play a range of ecological roles. Those species need to be described, and their phylogenetic relationships established, and good keys need to be constructed for them. Sabrina’s in her office now, surrounded by specimens. She’s on the case.


Rochefort, S., Giroux, M., Savage, J., and T.A. Wheeler. 2015. Key to forensically important Piophilidae (Diptera) in the Nearctic Region. Canadian Journal of Arthropod Identification 27. dx.doi.org/10.3752/cjai.2015.27


About terry wheeler

professor, museum director, entomologist, ecologist, naturalist
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2 Responses to Who’s that fly and WHAT is it eating? A new paper from the lab

  1. Nice post, and great work. And I got a little Alice’s Restaurant flashback too: “With arrows and circles showing important things” – what about the paragraph on the back of each one, explaining what each one was?

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