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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Random Insects & Guitar Music

I thought I would try something different with this ‘one minute bugs’ video. Let me know what you think!

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“Backyard Insects”

“Garden Pests, Diseases & Good Bugs”

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(Don’t Fear) The Hippoboscidae

I spent most of today with a fly. That may seem like a huge waste of time, but this was no ordinary fly – it was a wallaby fly. The closest I usually get to one of these flies is when I see a wallaby in the garden furiously flicking its ears trying to dislodge one. The individual here took a liking to me in the garden, and hitched a ride inside.

Flies of the family Hippoboscidae are all blood-sucking ectoparasites, i.e. parasites that live on the outside of their hosts. These flies usually cling to the hair of mammals or feathers of birds depending on the fly species involved. They have characteristically flattened bodies, powerful legs, and fishhook-like claws (clearly visible in the image below). You can see now why they are known generally as ‘louse flies’. There are more than 200 species found throughout the world (30 species here), and about 75% of them are ectoparasites of birds.

Wallaby Fly Hippoboscidae

Hippoboscid flies are quite particular about their hosts, for example flies which feed on mammals are not found on birds or vice versa. Back in the 1930’s research was conducted to determine if pigeon louse flies (Pseudolynchia canariensis) could bite humans and survive on human blood. The conclusion? They will bite humans when given no other choice of warm-blooded host. In other words, only when they are forced to. In case you were wondering – I wasn’t bitten.

Farmers in cooler regions of Australia may remember the introduced hippoboscid species Melophagus ovinus known as the ‘sheep ked’ or ‘sheep-tick’. In the past heavy infestations of this pest could cause anaemia in sheep, but modern farming practices have made occurrences of this pest quite rare. If you want to know more about this pest go here.

Green peach aphid giving birth to live young

While reading about hippoboscid flies I learned a new phrase – ‘adenotrophic viviparity’.  I was familiar with ‘ovoviviparity’, where eggs are held within females until they hatch internally, and the females give birth to live young. The picture above shows a green peach aphid doing just that. Adenotrophic viviparity is where eggs hatch inside the female, and the larvae are fed internally until they are mature enough to pupate. The larvae pupate immediately after being deposited by the female. The vulnerable larvae are therefore only momentarily exposed to predators.

I photographed the wallaby fly on the back of my hand in an attempt to show that it was a bloodsucker. It was also a skittish critter! Towards the end of the shoot it flew off my hand and landed on my black T-shirt – camouflaging it beautifully. It wasn’t until it crawled onto my face that I knew where it was. “Perhaps I’ve got enough photos now”, I thought. I hastily retrieved the fly and released it outside. Look out wallabies!

Many of you will have noticed that my post title (Don’t Fear) The Hippoboscidae references the 1976 Blue Oyster Cult classic (Don’t Fear) The Reaper. This song has had several lives including the original (link), the merciless Will Ferrell et al parody (link) – where the line ‘more cowbell’ originates – and the fun version with cowbell (link) by Leo Moracchioli.

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