Two Wings, But Not A Bird

I cannot put my finger on an insect and call it my favourite. Yes, the banner-bearers of the insect world, the butterflies and the moths, mesmerize me; I have an infatuation for the eagles of the insect world, the dragonflies and the damselflies. I adore the champions of this age, the beetles, the musicians, the piercers, the jumpers – one name is not enough to describe them – the true bugs. And the most industrious, the ants, bees, and wasps, the immortal cockroaches, the architects – the termites, the hunters and the herbivores, and all the rarities in-between with their own ingenious lives – they all amaze me equally. But the one that held my fascination for the longest time are also the most infuriating to understand, and they happen to be omnipresent.

It flies! A male horsefly struts his stuff by hovering mid-air in a large courtship ball.

This bias lies in you too. After all, it is not the butterfly that we recognize as soon as we begin to identify with the world. Nor the birds. It is that other two-winged entity: the fly. In our lives, we’ve fixated on flies more than any other animal, but for all the wrong reasons.

The infamous Anopheles, this one content with cattle's blood.

Flies truly grossed me out with The Fly (I & especially II). It took the axiom “flies kill” to another level – beyond space and time. In reality, they are way scarier – I give you that. Flies, unbeknownst to them, might I add, help spread the most horrible of diseases. They are responsible for most number of human deaths. They cause secondary infections, they spoil our food, they lay eggs on us and their larvae feed in us, and if you’re sensitive enough, their wing-beats alone can drive you crazy in the nights.

Our association with flies, however, has been limited. If you have an affection of the butterflies, it is generally for how beautifully they have evolved; how effortlessly they glide through the skies, elegantly perch on flowers, and fashionably unfold their delicate proboscis to sip nectar. Flies are a bit problematic to understand.

This fascinating mass of maggots of the dark-winged fungus gnats observe the "strength in numbers" behaviour by appearing like a caterpillar, or a snake.

We know them for that cold, wet feeling they give when the land upon us. We swat them when we see them on the table, and curse under our breath if they sit on the food. And their larvae are found in the most detestable of places. Our opinion about flies, in general, is based on our own limits of understanding, but I won’t blame you for it. It began in the ancient times – there is a demon, Beelzebub, also known as the lord of flies because he controls the spread of diseases. We used DDT rampantly on crops as well as against flies – particularly for mosquitoes – and ended up with a catastrophe that woke us from our ignorant little abodes.

You probably know by now what I’m going to talk about. I’ll start with this: In ecology, you know something is wrong when you know something for all the wrong reasons. The most infamous ‘something’ today are the flies – the whole lot of them – in the order Diptera, the third most diverse insect group in the world.

A few days ago, researchers found that flies carry many more harmful bacteria that can cause diseases than we previously thought (Junqueira et al. 2017). The study identified about 316 bacterial taxa on the surface of blow flies (blue-bottle fly) and about 351 on house flies (based on a certain method of identifying the Operational Taxonomic Unit of the bacteria) – most of them present on the legs and wings of the flies. The researchers identified at least 33 bacterial species associated with diseases in plants, animals, and humans.

On the other hand, a hover fly, Mesembrius sp., is exclusively a flower-visiting species, like the bees.

It was widely reported, with titles on the lines of: don’t eat food if a fly lands on it (The Telegraph); why you should never eat off your plate after a fly lands on it (Daily Mail). For most of us with relatively low understanding of the fly diversity, sensationalist news reports make flies appear as something like a demon, while the study focuses explicitly on two species of flies – and adds a cautionary line on the ultimate reasons for spread of diseases: The risk of infection ultimately depends on host susceptibility and contact with the agent transported by the insect vector, which moves from one reservoir to another (pg. 7 of the article). In other words, cleaner surroundings may have flies present, but they need not necessarily transport harmful bacteria to infest you. Also, they don’t do it intentionally; the bacteria they carry come full circle from humans, who, surprise-surprise, are almost always the source of these infections. For instance, several bacteria found on these flies cause a variety of nosocomial infections – diseases originating in a hospital – and most because of lack of hygiene.

On the other hand, a long-legged fly, a predatory species, attempts a somersault to distract you from all the talk of diseases.

The study aims to scientifically highlight the role of two species of flies as vectors of diseases – for humans as well as animals and plants – and to use it as “an effective tool for vector control programs and public health environmental surveillance.” It does not intend to demonize flies – but that is how we generally see it.

This makes us raise questions like: what if all the mosquitoes were killed (many have also very nicely explained why that is a bad idea – see the SciShow video and read this reddit thread). We ponder upon such grand-esque questions because mosquitoes spread deadly diseases, but as a matter of fact, only about 3% of mosquitoes bite us, even fewer spread diseases.

Toxorhynchites is a mosquito, but there's something about them:
their larvae breed in tree holes where they feed on other mosquito larvae, and as adults most are flower-visitors and pollinators. This fellow was feeding on a sarso flower in central India, also potentially aiding in pollination.

These questions generally follow-up with such questions: what is the role of mosquitoes in an ecosystem? This is sort-of difficult to explain, but, generally, every organism plays some role in the ecosystem, which is why it exists. Mosquitoes in particular are important in the web of life – they are pollinators, they are a source of food for fish as larvae and birds and other predators as adults, and some are predatory themselves.

A small, inconspicuous member of the Lauxaniidae family feeds on the pollen of the ephemeral Karvy which flowers
once in seven-eight years. This family is most common in the forest understorey, but is yet to earn a common name.

These questions attracted me to flies like flies to carcass. I wanted to know how many are there, how many are good and bad – an ethical conundrum in ecology, I agree, but a necessary-evil nonetheless, and I will explain you why shortly, and ultimately, what ecological role do they play. I started documenting flies ten years ago in my hometown of Thane/Mumbai and gather information about them. It wasn’t like seeing a butterfly or a dragonfly and quickly posing a query on an online forum. It was rather rudimentary (today, one of the best resources on flies is The “new” Diptera Site – run by an active community of fly watchers from across the world). Diptera is generally well documented in India, but it must be said that the Diptera of India has not seen the light of the day.

The upside of seeing flies is that for every butterfly or a beetle, you will find at least two flies! They’re everywhere – and I couldn’t emphasise on their omnipresence enough.

In this megacity of Mumbai, the order Diptera is represented by at least 50 families – there are likely to be more – encompassing 78% of the total family-level diversity of the Western Ghats and 57% of India’s diversity. How in the world do so many live in this metropolis, and, where?

Not a dragonfly! This is Systropus, a bee fly, a fly of forest edges and meadows
where they gaily sip nectar with their counterparts, the bees.

Fortunately, the metropolis of Mumbai is one of the largest in India – a whole of 4312 sq. km. – with the most diverse topography, from the rocky and sandy seashores to estuarine deltas to coastal tropical forests to sub-altitude semi-evergreen forests of the Western Ghats. It has everything that flies want, including a bustling human population, miles of open sewage canals and garbage dumping sites. Flies occupy every niche available in Mumbai, but there is a slight difference in where they are found. By segregating 16 microhabitat types the flies were found in into three habitats; natural areas, mixed habitats, and urban areas – there was a distinct trend on two fronts: where the flies are most diverse, and which flies are found in the least diverse areas. If you thought flies are most diverse in polluted, unhygienic places, you’re wrong. Most flies were found in natural areas than mixed, and least in urban, but generally, their distribution relied largely on the larval habitats.

This dull, drab-looking fly in the family mostly known for their pestiferous nature, Muscidae, is Ceonosia, a predatory fly
that scans gardens and orchards hunting for unsuspecting, and pestiferous, insects.

Finally, the ethical conundrum in ecology, of the good vs evil, was dealt with to dissuade the general negativity towards flies as a large, diverse group of insects, because of a select few species. Flies were segregated into “beneficial” and “pestiferous” categories based on their ecological functions. Of the 50 families, 66% fell in the beneficial category for the roles they play in an ecosystem, and 34% in the pestiferous category for causing diseases or economic losses. Both the sides were weighed to emphasise on their importance in an ecosystem, especially because, so far, the emphasis has mostly been on their pestiferous nature. What I found from this study is that flies are quite diverse in the metropolis of Mumbai, but at family-level, the diversity of the beneficial ones is more than the pestiferous ones.

This fly is ridiculously common on dung but extremely hard to see because of its small size, and hard to remember because of its long Family name - Sphaeroceridae.

Do not let that business of flies on a pile of garbage alarm you – take caution by all means – but also know that they’re a fraction of the fly diversity of your city – and they alone shouldn’t represent the marvellous diversity of this gorgeous group of insects!

A pair of crane fly, Pselliophora latea, is one of the largest and prominent species found across India. They are rather common close to swampy areas high in organic content, such as areas with seeping sewage, surrounded by good plant cover.
The one perched is female, and the one hanging with feathered-antennae is the male.

Fly watching is like observing butterflies or chasing beetles – you go to the most beautiful wilderness areas and see them buzz around flowers, like bees (flies are likely the second-most important pollinators), or just sitting and plotting their next move – but not quite. You also go see them on dead things (flies are the most important insects in forensic sciences!), including animal carcasses and their faeces where they initiate the decomposition processes. You also must visit garbage dumping sites and sewage areas where some of the most beautiful flies breed.

And while you peer into the substrate be fully aware of others wondering what fetishes you foster.

In other words: welcome to the world of flies.

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The abstract can be read here: http://threatenedtaxa.org/index.php/JoTT/article/view/2742

The entire paper (much more elaborated than this article) can be read here: http://threatenedtaxa.org/index.php/JoTT/article/view/2742/4208

You can also directly download the paper from here: http://threatenedtaxa.org/index.php/JoTT/article/download/2742/4208