The Inside Out of Flies

Flies do not get a lot of love. Their culinary choices, from cow-pats to corpses, do not endear them to us. Add to that that the order Diptera also hosts mosquitoes, called our deadliest predator by some authors, and you can begin to see why. Entomologist Erica McAlister, the senior curator for Diptera at the Natural History Museum, London, is on a mission to change your mind. Chances are you never have been able to admire a fly close-up.

McAlister previously explored the different lifestyles of flies with her very successful book The Secret Life of Flies. Now she returns with The Inside Out of Flies in which she marvels at their anatomy. After an initial look at the larval stage, she takes a head-to-toes trip along their segmented bodies.

Part of this book, of course, relies on a certain freakshow factor and McAlister clearly delights in her role as curator of curiosa. Behold the Pipunculidae or big-headed flies, whose eyes are so large that they look like flying microphones. Marvel at the incredible Mydidid fly, Perissocerus arabicus, whose antler-like antennae make it look like a miniature flying reindeer. Gaze upon the amazing humped thorax of the family Hybotidae. Or witness the aptly named mantis fly of the genus Ochthera whose bulging front legs resemble those of, you guessed it, the praying mantis. And do not get me started about the chapter on genitalia – it is enough to make a grown man blush.

And it has to be said, the variation in anatomical structures is wild. Her vivid descriptions will regularly make you do a double-take: “did I really read that right?” She supports this throughout with numerous beautiful close-up photos and scanning electron microscopy pictures. Clearly, I need to reconsider getting Marshall’s book Flies, as their anatomy is both fascinating and beautiful.

Not only is her subject matter engrossing and outlandish, but McAlister is also enthusiastic and witty. She marvels at blackfly larvae that “resemble members of a rather slow-paced Hells Angels gang [...] as they ride, not on a motorbike, but on a crab or a mayfly to catch food”. She had me in stitches with the kinds of personal revelations that only a biologist would think of writing down: “Never have I thought that mammals were more disappointing than when I first compared their genitalia to that of flies”. And there is a streak of eccentricity in her fascination, such as the joy of watching decomposing wildlife in her garden to see the flies it attracts.

But The Inside Out of Flies is much more than just a carnival of the bizarre. McAlister introduces plenty of serious biology here and mines the research literature for little-known but captivating nuggets. The taxonomy of flies and the use of the number and position of hairs and bristles (chaetotaxy) to tell apart species. The hidden processes that happen in pupae during metamorphosis that are now being explored with micro-CT scanning. The structure and function of the individual ommatidia that make up the compound eyes of insects. The flight mechanics in the thorax that allow flies to beat their wings at such high frequencies. Or the different hypotheses of how insect wings evolved.

There is a third strand to this book that shows that fly research is good for more than just a few giggles and for satisfying the curiosity of scientists: the applications. Many Diptera are pests of crops or carriers of diseases such as malaria. This is where taxonomy, knowing which of the approximately 160,000 currently described species you are dealing with, suddenly is vital. Or where understanding the ins and outs of their reproduction (sorry...) can offer a new pest management strategy.

One of my favourite such spin-offs is forensic entomology and McAlister provides a delightful example. Can physical barriers such as zippers delay the arrival of maggots at a corpse? This involved fresh meat covered by zippers cut from different models of suitcases and female blow flies. It is one of those seemingly weird experiments that might have people roll their eyes and mutter something about their tax money. But forensic experts and the police, who regularly pull body parts from suitcases, are really keen to know the answer to help them more accurately determine time since death and solve crimes.

And there are plenty of other examples. Studying the role of fly antennae in flight finds its application in the design of new miniature robots. The incredibly fast reaction times of a fly’s brain could pave the way to faster supercomputers. And the details of how mosquito mouthparts break skin to draw blood are inspiring new polymer microneedles that are less painful to use and have all sorts of advantages over regular steel ones.

So how does this book compare to her first book? There are a handful of examples and anecdotes that ended up in both books, but the overlap between the two is really quite small. Out of the two, The Inside Out of Flies feels like the more “serious” – and I put that in inverted commas as there is plenty to amuse and amaze you here. McAlister is an inspired spokeswoman for dipterology and entomology more generally, combining a heartfelt sense of wonder at the small things around us with a knack for popularizing science. The Inside Out of Flies, together with its predecessor The Secret Life of Flies, are must-read books for anyone interested in insects. Jonathan Balcombe, whose book Super Fly will be published later this year, is going to have his work cut out for him to put a new spin on this topic.