"Ugly brute, nasty fly"

 You might remember that in my last blog update I wrote about how I had found some late Peacock butterfly caterpillars, and was wondering just why they were still around quite late in the season? Well, I may have an answer now, and it’s quite sinister.

The caterpillars all without exception made it as far as pupating, it was then, well, shortly after, that things got a little freaky!

Rather than the beautiful adult butterflies that I was expecting to emerge from the chrysalis', one by one, what you might describe as 'maggots' began to emerge.

Here's the progression from healthy chrysalis to what I am calling a maggot (more on that in a bit), and then eventually a pupa.

Now I apologise if this gets a bit wordy, but it is quite complicated and I have tried my best to abridge my original jottings to be as concise as possible.

It seems that this is not the work of a parasitic wasp, but a Tachinid fly: namely 'Sturmia bella.' A Tachinid fly that most sources state was first discovered here in the UK in 1998/9.

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Having seen that the Tachinid fly maggots/larvae emerged from the chrysalises and not the caterpillars, I was intrigued to know whether these flies parasitised the caterpillars themselves, or the pupae. Of course, if the answer was that the caterpillars were affected in this way, then why did the fly larvae allow the caterpillars to grow to maturity and then pupate before emerging?

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Then...how about the mechanics of it; do the Tachinid flies lay eggs directly on to the caterpillars? I have never seen any with eggs present myself. Do Tachinids have some kind of ovipositor that allows them to inject eggs into the caterpillars or even the pupae?

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So many questions: I was determined to try and find the answers, or at least some of them, myself. It transpired that none of these things were relevent to what actually happened. More on that in a moment, but let's take a break and consider something less gruesome shall we?

Take a look at this next photograph...

It looks like a couple of different species of woodlice doesn't it? Well the one on the right is a woodlouse. The other one, on the left is not 'Oniscidea' (Woodlouse) at all, but 'Lonchoptera' a Pointed-wing Fly larva.

Yes, strange as it may seem this little critter found in leaf-litter will eventually become a fly.

Come with me now if you will, into the world of micro-photography. 

Actually, I am not too sure this is micro, because I think that refers to anything that is 20x life-size or more, and I have not calculated the magnification here. 

There's not as much definition as I would have liked actually, because I used my (broken) MP-E65 lens with a 1.4 convertor at one end, and a reversed 18mm lens at the other. But it does show you just how amazingly beautiful a butterfly wing is at high magnification. 

Just the thought of nature having to create every one of those individual scales whilst the transformation is taking place within the chrysalis blows my mind.

Alright then, let's ditch the glamorous in favour of the grizzly and get back to the story I began this update with. It took a lot of searching/research to find answers to my questions, questions that perhaps I should have already known the answers too, but I just didn't and as I always say, 'never be afraid to admit you don't know'. 

In fact the Tachinid fly Sturmia bella may be partly responsible for the decline in  the Peacock butterfly population: it has certainly been blamed by some for the decline in the Small Tortoiseshell butterfly, which it also parasitises.

Here's a photograph I took of one that I saw emerge from its pupa...

And so, although some of these flies do lay eggs on caterpillars, held in place by a kind of glue; and some do have a modified ovipositor that allows them to inject an egg directly into the host, this species does neither of those things.

This particular fly has an even more ingenious method: it lays its eggs on nettle leaves knowing that they will get ingested by the Peacock caterpillars as the feed.

The Sturmia bella larvae then develop within the caterpillars and emerge just after the caterpillar pupates, killing the pupae in the process.

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I have read from several sources now that at least 80-90% of Peacock caterpillars fall victim to attack by Tachinid flies. WOW! only 20% at best survive to become adults: and even that fact is assuming they don't get predated by birds etc.

After all, it's just nature doing what nature does right? Everything happens for a reason. It's all part of the ecology of the natural world; things balance out...

r

 

Now there is a guy by the name of Patrick Barkham, who writes for The Guardian newspaper on natural history, who would do well to remember these facts.

In an article he had published about Sturmia bella, he wrote the following:

 Sturmia bella (how the person who named this ugly brute could call it beautiful is beyond me), is a species of parasitic fly.

This nasty fly was recorded for the first time in Britain in Hampshire 11 years ago.

Ooooh! That insensed me!

He just doesn't get it does he. Yet here he is professing to be a nature lover and somebody who understands the complicated life-cycle of insects and bugs. He has awards for his writing from the Royal Society of Literature! 

Ugly brute! Nasty fly!

Give over Patrick, we can't all be the pretty little butterflies you love so much - that doesn't make us less worthy! We don't parasitise caterpillars using some kind of absurd Machiavellian  style, evil plot. Come to think of it, we probably don't even know what we are doing is wrong, we are just pre-programmed to behave in this way to survive, to continue as a species. We have no more control over our actions than your precious butterflies. You of all people should know this?

I'll just add that I have emailed the guy at his newspaper for a comment, I will let you know if he responds.

Was it Aristotle who said 'The more you know, the more you know you don't know'? Or was that Joey Essex! I think it must have been Aristotle, because he was the founder of the Lyceum after all, and Joey Essex knows nothing about West End theatres (smiley face).

The point is that it's a truism: I am constantly adding to my knowledge of the natural world, only to find yet more that I don't know. Take these next couple of images for instance...

 

In fact, let's add another...

I have very little idea about just what any of these are; and this was from only one day. All I can tell you about the top 'thing' is that it was found on thistle and was actually moving!

The second photo is of something that I found under a willow leaf. A pupa/cocoon of some kind perhaps? 

The final image looks to me like it could possibly be a fungus-infected Click beetle larva, but I just cannot be sure. 

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Time for the sleeping sheep photo I think...