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
Species Profile

Eastern Band-winged Hover Fly

Ocyptamus fascipennis

Ocyptamus fascipennis adult, spotted at Algonquin Provincial Park, August 2019

When you’re interested in insects, you’re always going to be running into something new. There is always one more creature that you have never seen before, one more behaviour you haven’t heard of, and that’s because insects are incredibly diverse. Today, I’m going to pick out just one of the many species of insects to zoom in on, and explore its story.

The species I’ve chosen is Ocyptamus fascipennis, or the Eastern Band-winged Hover fly. Let’s start from the top: Ocyptamus fascipennis is a “True Fly”, a member of the Order Diptera, which is a division of the Class Insecta. Diptera means “two wings” which gives you the easiest way to identify this group of insects when you encounter them. Almost all insect groups have 4 wings (two pairs) but these pairs of wings have been modified into very different structures in different lineages of insects. For the True Flies, one pair of wings still provides lift and flight, while the other has been reduced into tiny knobs known as halters. These reduced wings act as stabilizers, giving the flies the ability to perform aerobatic feats of agility (as I’m sure we’re all familiar with in House Flies (Musca domestica)). The halters of Diptera are more than just balancing beams, they’re actually sending complicated signals to the fly about its aerial position.

Ocyptamus fascipennis is part of a Family of True Flies called Hover Flies, or Flower Flies (Family Syrphidae). The Syrphids are common insects in gardens where they feed on nectar and pollinate flowers. Because of this habit, many species of Syrphids have taken on the appearance of more conspicuous flower visitors such as bees and wasps, in order to gain some protection from the classic warning colours of black-and-yellow stripes. O. fascipennis in particular seems to mimic solitary wasps or types of parasitoid wasps with its elongated and narrow abdomen.

So far, we’ve been talking about adults of these flies, but all insects go through multiple life stages, some more dramatically varied than others. Diptera undergo holometabolous growth which is a fancy way of saying that they have life stages that look very different from each other and one of those stages is a transformation phase which is mostly immobile. When young hoverflies (larvae) hatch from eggs, they look very different from the adults landing and lifting from flower petals in gardens. Larval O. fascipennis have no wings, and no legs, and are sometimes known by the name that many fly larvae receive: maggots. O. fascipennis larvae don’t consume garbage or dead animals, but instead are active predators, squirming across leaves in search of their prey: aphids.

Stephen Marshall, in his incredible book about Insects describes Syrphine larvae hunting as this: “at night they move blindly among the aphids, grasping victims using typical maggot mouth hooks, then holding the doomed aphids up off the surface to consume the body contents.” (Marshall, 2006).

A Syrphine larva hunting a herd of aphids (photo credit: Christine Hanrahan)

It seems then that Flower Flies are very beneficial insects to have in the garden. They provide pollination for flowers, and their larvae consume plant-eaters such as aphids and related scale insects.

While I was unable to find very much information pertaining to Ocyptamus fascipennis specifically, one other member of the genus deserves special mention because of its interesting larval habitat: tank plants (Bromeliaceae). The Central American and South American species of Ocyptamus that inhabit these confined aquatic habitats (pools of water within the plant itself) ambush and consume other aquatic insect larvae that live in the plants alongside them. The larvae are even thought to use a paralyzing venom to subdue their prey (Rotheray et al, 2000).

All in all, Ocyptamus fascipennis and its relatives are fascinating flower flies with intriguing habits. I hope you’ve enjoyed taking a closer look at them today.

UPDATE NOVEMBER 2021: Near Point Pelee, Ontario, individuals of Ocyptamus fascipennis were observed apparently migrating. The flies were observed moving East to West along with several other insects including tens of thousands of potter wasps (Ancistrocerus adiabatus) (Skevington and Buck 2021). The authors of the paper note that insect migration is a largely understudied phenomenon, especially in North America, so further study is needed to figure out the details.

References:

Rotheray, G. E., M. Zumbado, E. G. Hancock and F. C. Thompson. 2000. “Remarkable aquatic predators in the genus Ocyptamus (Diptera, Syrphidae).” Studia Dipterolologica 7: 385-98. (full text available here: https://repository.si.edu/bitstream/handle/10088/17095/ent_FCT_89.pdf?sequence=1&isAllowed=y )

Marshall, Stephen. Insects: Their Natural History and Diversity. 2006.

Marshall, Stephen. Flies: The Natural History and Diversity of Diptera. 2010.

Skevington, Jeffrey H., and Buck, Matthias. 2021. “The first documented migration of a potter wasp, Ancistrocerus adiabatus (Hymenoptera: Vespidae: Eumeninae)”. Canadian Field-Naturalist 135 (2): 117-119.