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
Natural Curiosities

Natural Curiosities, Part 1: Emu Feathers

My wife recently ordered me a bag of assorted natural curiosities from a seller on Etsy, Biophilia Supply. They sell ethically sourced nature items for use in decoration or education. In my case, it was for education. I’ve collected the odd natural curiosity myself from time to time (a few insect exuviae, a few dead insects, and a few fossils) and maybe I’ll write about some of those at some point in the future. The excitement of this Biophilia Supply grab bag of items was the variety and rarity of the items themselves. Through this series of posts I’m going to explore the items I received, and the organisms they came from.

Emu (Dromaius novaehollandiae) Body Feathers

Name Discussion: Dromaius novaehollandiae. Dromaius means “racer” in Greek, and the species name “novaehollandiae” is a Latinized version of New Holland, which is what Dutch explorers and sailors called Australia for a while in the 1700s.

Range, Relatives and the Ecology of a Flightless Bird: I have never seen an Emu, except maybe in a zoo, because they live across mainland Australia (though they used to also live on the neighbouring island of Tasmania). There also used to be two other species in the Family Dromaiidae (D. ater and D. baudinianus), but they were both island populations exterminated by humans in the 1800s. Their feathers have “barbs so widely spaced that they give the plumage a loose hairy appearance” (Davies 2002). I’m not exactly sure why Emus have hair-like feathers, but they certainly don’t need them to be stiff like the flight feathers of many other birds because Emus can’t fly. Emus can grow to almost 2 meters tall, and are the second tallest bird in the world, only behind the Ostrich. Emus are nomadic birds, traveling to places that have recently experienced rain and will gather in large numbers at abundant food or water sources. Although they inhabit the edges of deserts, they are always on the move to reach the most productive areas. Another adaptation for their dry and difficult habitat is to eat the richest foods they can find: Emus eat fruit and seeds as well as various species of insects.

Photo By JJ Harrison (https://www.jjharrison.com.au/) – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=92381514

Next up: Bison hair, Porcupine quills or the shed skin of a snake.

Reference:

Davies, S. J. J. F. Ratites and Tinamous, 2002.

Categories
Species Profile

Introduced Pine Sawfly

Diprion similis

Diprion similis larva at Algonquin Provincial Park, September 2019.

Sawflies are a group of insects that many people haven’t even heard of. Part of the reason is because, in appearance and behaviour, they are like a hybrid between two major groups: their larval stages look like caterpillars (larvae of Butterflies and Moths ie. Lepidoptera), and their adult stages look like bees or wasps (Order Hymenoptera). Despite appearances and lifestyle, it is the latter category that they actually fall under: Hymenoptera which also includes the Bees, Wasps, and Ants. The major features that set sawflies apart from their relatives is that they eat plants, and they don’t have the constricted “wasp waist”. You might find this a little confusing, as Bees certainly don’t have an obviously thin waist, but they actually do have a constriction between their thorax and abdomen, it’s just more difficult to see than in many wasp species.

Like many insect Orders, the name Hymenoptera refers to a distinct aspect of the members’ wings (‘ptera’ is derived from the Greek for wing). Hymenoptera doesn’t have an easy translation though, like say Diptera for the True Flies (di = two, ptera = wings). The beginning part of the word is either from the word “hymen” which means membranous, or from the word “hymeno” which refers to the Greek God of Marriage. Hymenopteran wings are membranous, but they also have tiny hooks that link their fore- and hind-wings, meaning that they could be said to be “married” wings as well (Grissell, 2010). Whatever the case, the group is one that includes thousands of species of wasps, bees, ants, and of course, sawflies.

The common name “sawfly” is describing the way the female sawfly lays her eggs. Instead of a stinger or stinger-like ovipositor (egg-layer) at the end of her abdomen (like most of the other Hymenopterans), the female sawfly has a saw-like ovipositor, a cutting tool that she uses to open up plant tissue, and then inserts her eggs within.

This is what the Introduced Pine Sawfly (Diprion similis) does to pine needles. D. similis prefers White Pine (Pinus strobus) as its host plant (in North America), but will lay eggs and successfully grow to maturity on several other pine species. The female lays about 10 tiny eggs inside a pine needle (Cranshaw, 2004). After inserting the eggs, the female seals them in with a secretion that hardens for protection (Wagner and Raffa, 1993). The larvae that hatch from the eggs begin to feed on the pine needles. For the first part of their life, they will remain together but begin to disperse as they grow older. These larvae prefer to feed on needles that are at least 1 year old, probably because the younger needles are full of more toxins (Wagner and Raffa, 1993). As they consume needles, they grow, from 2.5 mm long upon first hatching to almost 3 cm before the larva is said to be “mature”. They don’t grow continuously, but rather have to molt and enter a new size class each time they’ve gained enough nutrients. For female larvae, they have six growth stages between molts and the males have five (CABI, 2020).

During this time, you would be forgiven for thinking they were caterpillars, because they look very similar. The way to tell caterpillars from sawflies is to count the number of legs. Their first set of legs will be six, and jointed for both groups, but they will also have a number of legs behind these called “prolegs”. If the larva you’re looking at has more than 5 pairs of prolegs, it’s a sawfly. Another giveaway is the distinct single eyes of sawfly larvae, as opposed to tiny ocelli (miniature eyes in clusters) in caterpillars.

Once they’ve reached their final larval stage, they spin a cocoon around themselves with silk, and transform within. Diprion similis larvae prefer to form their cocoons in the pine trees where they feed, rather than on the ground like many other sawflies.

In Europe and most of North America there are two generations per year, which means that what happens next depends on what time of the year it is. If the larvae have grown enough and created their cocoons in the summer, they will develop within in about 2 weeks into adults, but if they have reached this point near the end of fall, they will enter diapause (essentially insect hibernation) for several weeks before emerging in the spring (CABI, 2020). When they emerge, the adult sawflies are entirely different creatures, just as butterflies and moths are very distinct from their caterpillar young. The adults have wings, and with these they search for mates.

Adult Male D. similis, displaying the feathery antennae used to track down a female (Photo credit: Scott R. Gilmore.)

Males are attracted to females by pheromones (a chemical signal between members of the same species), as one would guess by the male’s elaborate antennae. The males can be attracted to a female across 61 m of open field, which is a great distance for an insect only a matter of centimeters long (Wagner and Raffa, 1993). Once mated, the female lays eggs in pine needles, and we are back at the beginning of their life history.

One note about mating: it isn’t necessary for the female to mate to be able to lay eggs. She shares with the other Hymenoptera a bizarre (to us) chromosome setup known as haplodiploidy. Females have one set of chromosomes (the mother’s) and males have two (mother and father). What this means in practice is that a female sawfly can lay an egg that will develop into a fully functional male offspring without ever going through the trouble of mating. This has implications for the spread of such organisms, as not all members of the population need to pair up to contribute to the next generation.

Which brings me to my final discussion of this species: they are commonly referred to as the Introduced Pine Sawfly because they were accidentally introduced into North America from Europe, likely in plant nursery stock imported in 1914. They have become well established in North America since then. Thankfully, they only very rarely reach a high enough population density to be considered an “outbreak” invasive species, and though they feed on tree leaves (needles), many predators and parasitoids feed on them (Wagner and Raffa, 1993).

The last time we were camping at Algonquin Provincial Park, I encountered quite a few of their larvae likely because they were in the fairly mobile phase before finding a spot to spin a cocoon (it was the end of September, the beginning of October). They may be an introduced species, and they may feed on White Pines, defoliating some of the branches, but as with any organism, they have a story all their own, and I think it’s worth telling.

Diprion similis larva hanging onto the end of a pine needle in Algonquin Provincial Park.

References:

Wagner, Michael R. and Raffa, Kenneth F. Sawfly Life History Adaptations to Woody Plants, 1993.

Cranshaw, Whitney. Garden Insects of North America. 2004.

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

Grissell, Eric. Bees, Wasps, and Ants. 2010.

CABI, 2020. Diprion similis. In: Invasive Species Compendium. Wallingford, UK: CAB International. www.cabi.org/isc.