The Flies of March

Australian readers of this post will be very familiar with the insects known as March flies. In temperate zones these flies are commonly encountered over the warmer months of the year, and are unwelcome guests on many camping holidays! Tropical species may occur at any time of the year. In other words March flies don’t appear exclusively during the month of March.


Perhaps the common name stems from the March flies of the northern hemisphere which may arrive during the northern spring (i.e. around March). Unfortunately those northern hemisphere March flies are in a different family (Bibionidae). I include a picture of an Australian bibionid fly (Dilophus sp.) below. As you can see it doesn’t look anything like an Australian March fly. The March flies we know are members of the family Tabanidae, and we have about 400 species of tabanid flies here in Australia.


Australian March flies are notorious for their painful bite, and some species are pests of livestock which gives rise to another common name for them – ‘horse flies‘. Male March flies don’t bite, they feed on nectar. It’s only the females that feed on blood, they need the protein to lay fertile eggs. There are some March flies (both male and female) that never feed on blood – they only feed on nectar. The beautiful Scaptia auriflua is one of those – just click this link to learn more about those.


Hows that for a proboscis (above)? No wonder it hurts. Female March flies puncture the skin with the spike you can see at the tip of the proboscis, and then mop up the blood with spongy mouthparts. They don’t suck blood like mosquitoes do. March flies tend to be fairly slow, especially when they have landed on your skin for a blood meal. They do a fair bit of investigating of the skin before inserting their spike, and are easily swatted away.

The larvae of common March fly species usually occur in damp soil, vegetation in swamps, and in river mud, where they prey on other insects. Adult March flies are themselves preyed on by other insects such as robber flies, reptiles such as skinks, and birds. They may be annoying to us (and in the case of some overseas species spread diseases) but they are part of the environment we live in. This post was inspired by the beautiful March fly below (I’m not sure of the species) that I found in my vegetable garden just the other day.



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Sheep in Wolf’s Clothing

Insects that are armed with powerful stings are often strikingly coloured to warn off potential predators – a strategy known as aposematism . A good example of this is the black and yellow colour pattern of the European wasp (Vespula germanica).

Vespula germanica

Some harmless insects take on the appearance of aposematic insects even though they are not actually dangerous themselves. Hover flies are an example of this. One common hover fly species the drone fly Eristalis tenax – is an excellent bee mimic, and was the star in a recent ‘one minute bugs’ video (link).

Other common hover flies (image below) are harmless flower visitors but their striking yellow and black markings superficially resemble the markings of bees or wasps. Bees and wasps usually have stings and consequently are left alone by many predators. Hover flies don’t have stings, so by adopting colour patterns similar to bees and wasps this affords the hover flies some protection. This defence strategy is known as Batesian mimicry.

Bee mimic

Now for a wee bit of history. H.W. Bates (hence ‘Batesian’) was the first scientist to conduct a major study on mimicry – in the Amazon Basin in the 1860s. Charles Darwin recognised Bates’s work on mimicry as critically important to the theory of evolution, and cited it extensively in later editions of his own great work The Origin of Species. Darwin appears to be quite a fan, because in a letter to Bates in 1862 Darwin wrote:

“Dear Bates. I have just finished, after several reads, your paper. In my opinion it is one of the most remarkable and admirable papers I have ever read in my life.  .  . Your paper is too good to be largely appreciated by the mob of naturalists without souls; but, rely on it, that it will have lasting value, and I cordially congratulate you on your first great work.”

I am particularly intrigued by insects which mimic other insects that would normally appear very different from their own body shape. It’s easy to see how a yellow and black patterned fly could look like a bee or a wasp (e.g. the hover fly), but how about a beetle which looks like a spider-hunting wasp? The yellow-horned clerid beetle Trogodendron fasciculatus (Cleridae) – image below – mimics the spider-hunting wasp Fabriogenia sp. (Pompilidae) – lower image.


If you place them side-by-side you might think the resemblance is only superficial – dark bodies and yellow/orange antennae. It’s when they move that you see mimicry at its best. Spider-hunting wasps move in a characteristically jerking manner and flick their antennae constantly as they look for spiders. The yellow-horned clerid beetle mimics these movements exactly, so much so that when you see one moving you would swear that it is a wasp. The beetle would then be completely safe from predators especially spiders. No sane spider would want to go near an insect that appears to be a spider-hunting wasp!

Spider wasp
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Hunting the Hunter (Part 2)

Hunting the Hunter (Part 1) was written about a year ago – you can read it here. That post was mostly about spider-hunting wasps of the family Pompilidae, and finished with the image below as a bit of a teaser to this second part.

spider fly

The image shows several fly larvae (the arrow-headed segmented hairy things) and lots of eggs (the black ovoid things). They are the eggs and larvae of flies from the family Acroceridae. Adult flies of this family may be known as ‘bladder flies’, ‘small-headed flies’, ‘hump-back flies’, or ‘spider flies’. The image below indicates how a couple of those common names may have come about.

bladder fly

Acrocerid flies are well known for having enlarged compound eyes that meet in the middle of their head, which probably provides an extended field of vision. The adults of some species have elongated proboscises, sometimes longer than their entire body. The individual pictured here is of the genus Ogcodes which has a very short proboscis.

The larval stages of acrocerid flies are endoparasitoids (i.e. internal parasites) of spiders. After a pair of acrocerid flies have mated, the female flies deposit tiny eggs en masse on dead twigs, grass stems, fences, wires, and other structures. The eggs are so small the egg mass looks like soot at first sight (as you can see in the image below). There may be as many as 5000 ‘microtype’ eggs in each egg mass – all of which may hatch into spider-seeking larvae.

Ogcodes eggs

First instar larvae (such as the ones in the image at the top of this post) are free-living planidia which actively seek out suitable spider hosts. The spines that you can see on the larvae must really help when climbing onto a hairy spider.

Once an acrocerid larva finds a spider, it burrows inside, attaches to the spider’s book lungs, and begins feeding on its body fluids. The larva moults three times, growing larger each time, feeding all the while. The final instar (growth stage) larva kills the spider just prior to emerging from it. The acrocerid larva consumes the entire contents of the spider’s body, leaving an empty exoskeleton. The larva then pupates, and an adult acrocerid fly eventually emerges from the pupa. The image below shows a male (left) and a female (right) of the genus Ogcodes.


Many people think of flies as being either dirty (as in the case of house flies Musca domestica) or annoying (bush flies Musca vetustissima). There is much more to flies than that! There are about 7000 species of flies described in Australia so far, and there may be as many as 30,000 species here. If acrocerid flies are anything to go by, there must be lots of flies with amazing life cycles that we don’t know about yet!

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