A photo of a fly

When I was aged 10 or so, I was fascinated by lungfish. This pioneering group that built an evolutionary bridge between sea and land life, survived the extinction of the dinosaurs and still boasts three genera on three continents today, gripped my imagination. The wondrous, beautiful complexities of the natural world can grip the mind of children (and adults) and really engage them in lifelong learning – a passion that a future decade of exam-focused schooling was largely to beat out of me, requiring later rediscovery.

Although with one of my summer biology readings, I shifted my interest to an even more unlikely subject, flies, which I learnt have been the subject of longtime fascination for many. The diarist Samuel Pepys records meeting the English polymath Robert Hooke in the street on 8 August 1666, and hearing from Hooke that he could count the number of strokes in a minute made by a fly’s wings by matching it to music.

I’d challenge anyone who’s interested in the wonders of the natural world, the amazing creative force that is evolution, who really wants to understand how all of our amazing ecosystems function, not to be gripped by Erica McAlister’s The Inside Out of Flies. You don’t even have to read a lot of the packed detail of its 288 pages. You could just look at the pictures, in sumptuous colour and glorious detail, as might be expected from a publication from the Natural History Museum.

Even though this is a small, paperback-sized book, you could easily sit it on a coffee table and invite visitors to browse the wonderful images, from the amazing Pipunculidae, their massively enlarged eyes making them look like a flying microphones, to the wonderful peacock fly, Callopistromyia annulipes, with wing patterns that match their name,

While the book is arranged in chapters according to anatomy – and has a great deal of detail about that – starting logically enough with antennae and working through to terminalia, it is very practically focused on how flies fit into their worlds, physically and ecologically. So McAlister explains how flies get wings out of the way when not in use, by means of “a musculature attachment to a hardened plate at the base of the wing called the third axillary sclerite, and it is this that enables them to flex the wing backwards to fold across their abdomen”. She notes that as a lecturer, she used to demonstrate this by flapping her arms around in the classroom, only to see students doing the same in exams to remind themselves of the mechanism. This would definitely enliven a social session of tea and scones.

As might the knowledge, for those who reel back from a traditional association of flies and dirt, of just how fastidious flies are about personal hygiene. McAlister tells us: “The cleaning of each part of the body is organized hierarchically – with the most important parts needing to be cleaned first and more regularly – eyes antennae and head”. She describes a fascinating if disturbing experiment with Drosophila, the laboratory standard species, that removed the front legs, which they would usually use to clean the most crucial parts of their body. “After a couple of days, the flies without had twigged that they were lacking front legs, and so they started clearing themselves with their middle set of legs.” McAlister says there’s a lot of research being undertaken now to try to understand that learning process.

For those of a stronger disposition, the book contains many accounts of how flies can fit into, and enhance, human lives. You might not previously have known how the faeces of midge larvae, who live in the dirty layer in sewerage treatment plants (“schmutzdecke” in wonderfully evocative German) – helping clean up water supplies. One group of researchers found it made up 23% of the sand layer, hugely adding to its surface area and structural complexity, “enabling more organic material to bind to it thus trapping it in the sediment”.

That’s a group that probably has little problem sniffing out their desired location, but while smell is vital to most flies, for some their abilities are astonishing. Take the truffle-finding flies of the genus Suillia. One species finds winter black truffles, another summer lighter versions. Their physical abilities amaze in many directions: a male horse fly has been measured as travelling at 145 km/h. These flies, in pursuit of passing females, also perform what is in effect an Immelman turn, as developed by a German World War One fighter pilot, “pull his plane up into a half loop, and then half roll it, increasing both height and then rapidly reversing direction”.

Although be warned, this is a book that might give some nightmares. The inspiration for many a horror movie has surely been drawn from a genus like the Pseudoacteon, the “ant decapitators” – whose larvae crawl in and detach it, giving them a wonderfully tough space in which to pupate. Or the assassin flies, which McAlister claims are “some of the fiercest and most successful predators on the planet”. Proctacanthus milbertii on the prairies of North America can each eat up to two grasshoppers a day, seeing up to 2% of the entire population killed in a day, each solo hunter feasting on a grasshopper more than double their size (only the inside squishy bits, not the exoskeleton).

Of course, as with any biology book, McAlister is not only describing new wonders being found every day, but also just how threatened so many of those wonders are. It might not ever win the popularity of a panda or a tiger, but the life of certain Calliphoridae (the group to which blowflies belong), which live and feed in the egg masses of a particular India frog as a larvae, then when stuffed with food, hang from the nest which is usually over water, lower themselves on a thread into that water then swim for the shore, inflating an air sac for buoyancy. “The habitat where this research was conducted is being destroyed at a rapid rate due to tremendous urbanisation pressures.”

There’s no risk of flies as an overall group disappearing any time soon, but the fossil record shows how much change there’s been in the past, since they first emerged 60 million years ago in the Early Cretaceous. Then there were no flowering plants, but some flies, including the spectacular, long extinct Archocyrtus kovalevi, fed on – and pollinated – plants like conifers. The world changed, and fly species did too – but even many of these complex, varied insects are finding it tough in the world we’ve made.

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