Categories
book review

Flies: The Natural History and Diversity of Diptera, by Stephen A. Marshall

People are always going on about how Beetles are so diverse, biologists are always explaining to theologians that God must really love Beetles*, and whenever anyone asks “What’s the most diverse group of organisms?” Beetles are always top of the list. UNTIL NOW.

*in case you don’t know the anecdote this is referring to, the earliest source (according to quoteinvestigator.com) runs thus: “There is a story, possibly apocryphal, of the distinguished British biologist, J. B. S. Haldane, who found himself in the company of a group of theologians. On being asked what one could conclude as to the nature of the Creator from a study of his creation, Haldane is said to have answered, “An inordinate fondness for beetles.”” (Hutchinson 1959).

Stephen Marshall proposes in his magnificent volume on the diversity of flies that there are historical reasons why beetles are held up as so diverse when the truth is that they might just be more closely studied than other insect groups… other groups like the order Diptera (true Flies), for instance. And if you read through this 600 page volume loaded with superb photographs and covering every single family of flies in some detail you will come away with the powerful impression that Stephen Marshall is on to something. Flies, a group often neglected because they don’t always photograph well, many look very similar to each other, and a lot of them have distasteful feeding habits, are showcased as the hyper-diverse evolutionary marvel that they are.

Metallic Green Long-legged Fly (Condylostylus sp.), photographed in my backyard, June 2018. I’m just going to post some of the many interesting flies that I’ve photographed myself throughout this article. Stephen Marshall mentions that digital photography is opening up the realms of entomology to amateurs in a way that hadn’t been possible in the past. I wholeheartedly agree!

The book’s first part: “Life Histories, Habits and Habitats of Flies” runs through a sampler of what flies do as larvae and adults. This includes the life cycles of Diptera in general, but elaborates on more specific groups where appropriate. Other sections in this part describe flies interacting with plants, fungi, invertebrates and vertebrates. This entire section comprises about 90 pages and goes into considerable detail on specific guilds* such as the worldwide coastal communities of “wrack flies”, flies that have larvae that feed within decomposing piles of seaweed washed upon shores. Along with the various interactions between flies and invertebrates, this section also includes a discussion of the many human diseases caused or carried by flies such as mosquitoes (Family Culicidae) or house flies (Musca spp.).

*A guild is a group of animals that are united by a common feeding strategy or resource use, but not necessarily united in relatedness. For example, flies from different branches of the Dipteran family tree are considered part of the leaf-mining guild if their larvae produce mines in leaves.

Eutreta novaboracensis, a Fruit Fly of the family Tephritidae, photographed in my backyard, June 2018.

The second part of the book is titled “Diversity” and reading through this catalog of fly families and subfamilies truly does drive home just how incredibly diverse the Order Diptera is. Each chapter covers a large portion of the fly family tree and opens with a diagram of the proposed relationships between the fly groups within. This opening section of each chapter moves from family to family, and describes the basic characteristics of each group detailing subfamilies where possible as well. Within these descriptions are not just lists of characters used to distinguish one family from another but also the basic biology of each group when known. A couple of key things to note here: even when dividing up the flies into smaller and smaller groups it can be hard to generalize because you are still dealing with huge swaths of species in some instances and in others you are simply dealing with species doing very different things despite their close-relatedness. Marshall does a good job of explaining this and I’ll provide an example here from the section on Tipulidae (the Crane Flies, of which there are more than 15 000 described species): “Although most larvae with known biologies are saprophagous and eat microbe-rich organic matter (normally, decaying plant material) in wet environments, some crane flies are predaceous, fungivorous or phytophagous… Some groups have become specialists in extreme environments such as caves, marine intertidal zones and deserts, but most occur in humid forests and wetlands. Most Tipulidae are unknown as larvae.” (Marshall 2012 p. 110).

Crane Fly (Tipula sp.) photographed on the Lynn Valley Trail, May 2018.

The above quote demonstrates the way in which Marshall overviews the lifestyles of the fly groups providing tantalizing glimpses of their diverse life histories, but it also provides an example of something that is rife within the 600 page volume: the overwhelming amount of flies or fly habits that are unknown. To demonstrate, here are some quotes from throughout the book (Marshall 2012):

Valeseguya rieki is known only from a single male specimen” (p 136)

“Larvae and larval habitats of the Lygistorrhinidae remain unknown” (p 141)

“Nothing is known of the biology of these obscure little flies [Ohakunea]” (p 141)

“adults of Oreoleptis (and thus the family Oreoleptidae) have yet to be collected in the field” (p 198)

“The 500 or so species of Acroceridae occur in every part of the world, but most are known from only a few specimens” (p 205)

“Essentially nothing is known about the biology of either Apystomyia or Hilarimorpha” (p 235).

“Even though signal flies [Platystomatidae] are usually conspicuous and attractive flies, many species remain undescribed.” (p 332).

“Larvae are unknown for most species in the family [Lonchaeidae] and little is known about behavior” (p 335).

“The biology of most Pallopteridae species remains unknown” (p 339).

“The truth, however, is that we know almost nothing about the life histories of these bizarre flies [Ctenostylidae]” (p 340)

“Nothing is known about the biology of this group [Nothybidae]” (p 348)

“Despite a worldwide distribution, with about 140 known species spread over every zoogeographic region, not much is known about asteiid biology.” (p 363)

“Nothing is known of the biology of the Neotropical dwarf fly genera [Periscelididae]” (p 365)

The quote list above is not comprehensive, but rather a sampling to show some of the many groups of flies that are mysterious despite their ubiquity in some cases. I don’t want the quotes above to be taken as evidence that the book contains little in the way of information on the flies of the world, seeing as so little is known overall. On the contrary, this volume is chock-full of biological details found nowhere else except the specialized literature and I found myself blown away by many intriguing and fascinating descriptions of fly families and subfamilies. Below are a few of the more interesting groups I had never encountered before reading through this book.

Frog midges (Corethrellidae) are attracted to singing frogs where the females feed on the frog’s blood. Some Phorid flies lay their eggs inside ants, where their larvae consume the ant’s head from the inside. After feeding within, the larvae decapitate the ants and pupate within the armored shelter before emerging as adult flies. These flies are known as ant-decapitating flies, and there are more than 300 species of them in the genus Apocephalus. Vermileonidae is a family of flies known as “wormlions” which are essentially the antlions of the diptera, their larvae constructing cone-shaped pits to trap wandering insects for prey. The Fergusoninidae is a family of flies that “develop only in galls induced by a specialized and codependent group of nematodes” (Marshall 2012, p 366).

Probably my personal favourite are the smoke flies. The smoke flies, platypezid Microsania spp., are attracted to fires (even campfires) but are rarely seen elsewhere. The smoke fly swarms are often followed by the predatory empidid dance fly Hormopeza which “seems to be a specialized predator of smoke flies. Like Microsania, the smoke dance flies are rarely seen except when they appear in plumes of smoke.” (p 298). I feel like the smoke flies, a group of species that can be attracted to something as common as a campfire, and yet are known from basically nowhere else (and thus poorly understood biologically) perfectly encapsulate the mystery and wonder of flies that I have gained from reading this book.

All of this fascinating information is found within the comprehensive and authoritative text, and after going through family by family in this fashion, each chapter in the “Diversity” section has a “photographic guide” portion which covers representatives of most subfamilies with further notes on natural history and significance of genera pictured. The scope of the pictures is mind-boggling and further bring home the diversity of flies, as well as their surprising beauty.

Transverse-banded Flower Fly (Eristalis transversa), photographed in my backyard, September 2018.

The final, shortest section covers collecting, preserving and identifying flies, and contains notes for those interested in starting insect collections of their own (as in, pinned specimens) as well as keys for identifying the major fly groups.

I can honestly say that if this book were published with only the text portions I would buy it because the text is just that valuable in overviewing the enormous diversity of the fly families. And I can also say that if this book were published with only the pictures and captions, I would also buy it for the incredible amount of biodiversity on display, captured in wonderful images of flies from around the world.

I cannot recommend this book highly enough. If you are an insect enthusiast, if you are at all interested in the diversity of life and if you enjoy gasping at revelations about the tiny wonders that flit around the world you have to read this book.

References:

Hutchinson, G. E. 1959. “Homage to Santa Rosalia or Why Are There So Many Kinds of Animals?” The American Naturalist93(870), 145–159. http://www.jstor.org/stable/2458768

Marshall, Stephen A. 2012. Flies: The Natural History and Diversity of Diptera.

For previous book reviews, see:

The Paleoartist’s Handbook, by Mark Witton

The Social Biology of Wasps, ed. by Kenneth Ross and Robert Matthews

Pterosaurs, by Mark Witton

Flora of Middle-Earth, by Walter Judd and Graham Judd

And for a podcast review, see:

The Field Guides

Categories
June 2021 Observations Nature Observations

Flies Falling to Fungi and Other Dipteran Observations

In my backyard, I usually see a lot of Flies of various species, many of which I find difficult to identify. Flies don’t have the obvious characters or colours that other Insect groups have such as Butterflies and Beetles. There are two broad divisions of the Order Diptera (that is, the True Flies) which can be fairly easily distinguished. Nematocera roughly translates as “long-horned”, referring to their relatively long antennae and includes the Midges, Mosquitoes, Fungus Gnats and many others. Brachycera means “short-horned” and includes the House Flies, Carrion Flies, Fruit Flies, and dozens of other massive groups. As I mentioned in my post about observations at my Parents’ house, I’m reading through Flies by Stephen Marshall and it’s only reinforcing the bewildering diversity of Flies and Insects in general.

Incidentally, a Fly that I can’t identify landed on the book Flies as I was reading it in my house. There is a Family of Flies called the Ironic Flies (Family Ironomyiidae), but unfortunately this definitely isn’t one of them. That would have just been too perfect. My best guess for this Fly is a Fungus Gnat or a related Family (Sciaroidea).

A Mystery Fly that landed on Flies: The Natural History and Diversity of Diptera by Stephen Marshall while I was reading it.

All that being said, there are some Flies that I can now identify on sight such as this Common Picture-Winged Fly (Delphinia picta):

A Common Picture-Winged Fly in my backyard.

Others easy to identify (to Genus) are the Condylostylus flies which hunt small prey and display on leaves worldwide. 

Bright Metallic Green Condylostylus are easily recognizable Flies worldwide.

Another group of Flies that I’ve become familiar with have one of the most unsettling Family names ever: the Flesh Flies (Sarcophagidae). The three black stripes on the thorax distinguish them from similar-looking Flies (Marshall, 2012). To make them even more unappealing than their name, many of these Flies lay eggs that hatch immediately after they leave the female, or they simply lay larvae that have already hatched. There are about 3000 species in the Family Sarcophagidae, and the ones I see in my backyard are likely in the Genus Sarcophaga. Within the Genus Sarcophaga there are 800 species, so they are very difficult to generalize about, with some of their larvae feeding on or within other insects, consuming dead vertebrates, or specialist parasitoids of spider or grasshopper eggs (Marshall, 2012).

Flesh Fly, possibly of the Genus Sarcophaga.

Another Fly observed within my own house is likely a member of the aptly named Window Fly Family (Scenopinidae), as I photographed it on the interior of my back door window. Although this Family of about 350 species is associated with various habits and habitats, they are named for the handful of species that are predators of human-habitat insects such as Carpet Beetles (Dermestidae), which is likely what my Window Fly was.

Window Fly (Scenopinidae), likely one of the human-associated species in the Genus Scenopinus.

The most eye-opening Fly observation of the month has more to do with the fate of the Flies, rather than the Flies themselves. I found two Flies in my garden in a bizarre position, one at the very end of May and one on the 1st of June. I’m unable to identify either species of Fly beyond the fact that they’re both Brachycerans. Each fly was positioned at the end of a leaf, clutching it with its legs and they were covered with what looked like white dewdrops bursting out of their bodies on tiny filaments. The filaments emerging from the fly bodies (the Flies were also quite dead or at least incredibly still and unresponsive) must have belonged to a type of Fungi.

First Fly I found infected by a fungus at the end of May. All of the whitish flecks across the fly’s abdomen and thorax are fungi.

Many readers may be familiar with the incredible footage in BBC’s Planet Earth of the Cordyceps fungus infecting ant workers and forcing them to climb into the tree canopy in order to release the fungal spores upon death. What might surprise you is that similar insect-infecting fungi are found not only in tropical rainforests but around the globe, even in my own backyard in Simcoe, Ontario. In fact, Cordyceps itself occurs in parts of North America (into the Southern United States), where it infects insects and causes similar scenarios to the one depicted in Planet Earth (Eiseman and Charney, 2010). There is an entire order of fungi, Entomophtorales, in which most species infect insects and other arthropods. If you’re interested in similar observations, there’s a Bugguide page devoted to this sort of thing. I have no idea which species infected these Flies in my backyard, but it’s fascinating to know that these sorts of complex interactions are occurring right where I live.

Another Fungal-infected Fly I found at the start of June. I’m not positive, but the long threads surrounding it could be fungal in nature as well.

For previous June 2021 Observations, see:

Fuzzy Flies and Song Sparrows

The Wonders of Wrens

And for another post focused on a species of Diptera, see:

Species Profile: Eastern Band-winged Hover Fly

References:

Eiseman, Charley and Charney, Noah. Tracks & Sign of Insects and Other Invertebrates: A Guide to North American Species. 2010.

Marshall, Stephen. Flies: The Natural History and Diversity of Diptera. 2012.