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.

Trogodendron

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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This is not a bee


This ‘one minute bugs’ post is a video about one of the flies that mimics the European honey bee. You will also meet some crazy looking fly larvae! I must warn you that the video also contains a couple of illustrations that I created in Photoshop. They are a bit daggy but hopefully they help!

I hope you enjoy the video – as usual, being ‘one minute bugs’, it’s short and sweet! Let me know what you think. Please hit the subscribe button in the widget if you would like to receive email alerts about new posts. The subscription process is more than one click, but it won’t take too long!

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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.

Acroceridae

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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