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Wednesday, 13 August 2014

It's a tough life for the outdoor Swallowtails

* Warning - this post contains some gruesome photos of
predation and parasitism
! *

I have been watching four Papilio machaon Swallowtail chrysalises that I discovered outside whilst still caterpillars in pre-pupation. Some pretty horrible things happened to them!

But before I get to that, let's look at some caterpillars and their unpleasant demise. I found six of them dead with what looked like a sort of sooty mould on their bodies. I've researched and cannot find what it is. This didn't stop other bugs from checking them out, although I can't be sure they actually fed on the dead caterpillar because I wouldn't have thought it was entirely healthy to do so!

Bug nymphs checking out and possibly feeding on the dead caterpillar.
Note that little wasp on the right - that has significance later on in this story!

Here's another one I found hanging from a fennel stalk.
Some ants and bug nymphs checking it out.

An ant looking into what I think is a mouldy bit....
and see how deflated the caterpillar looks too.

Now chrysalises - remember the one that I got to witness pupating a couple of posts back? Unfortunately this is what I found happening the following morning. It made me sick to the stomach to see this after having watched the pupation as I felt closer to it because of that. I shouldn't attach human emotion to it but I couldn't help it. Ants have to eat too but it just seemed so unfair ..... and ugh!

This poor fresh chrysalis didn't stand a chance with a load of ants swarming over it.
After pupation you can see that the inside of the chrysalis is just yellow goo at this point.

Going back to the first chrysalis that I found, I just couldn't believe (1) how I even noticed it and (2) why it chose this spot to pupate in. I had bunged a pot containing Ophiopogon planiscapus 'nigrescens' by my potting shed as it was full of weeds and needed repotting. However I haven't had a chance to do that yet.....

You would never have known.....but there it is in the photo on the right.

Now we get on to the subject of parasitism. I did a little research after taking photos of these wasps and discovered an American site (link given later) which gave me a lot of very interesting info on Chalcid wasps. Somehow they are quick to discover the caterpillar in pre-pupation and hang around waiting for it to pupate, then lay their eggs in the still soft chrysalis. The poor caterpillar and freshly pupated chrysalis twitch a lot trying to dislodge the wasps but it's futile. Chalcid wasps by the way are supposed to be a gardener's friend and are used in biological control, as they keep down numbers of the less desirable Lepidoptera species. And the desirable ones too!  

No sooner had it settled down to pupate, the wasps arrived.
I don't know the ID of the larger one with the long antennae
but I later found out the smaller ones are Chalcid wasps.

Then blow me down if another caterpillar decided to pupate in the same plant pot! On this one I only spied the larger unknown wasp and a Red Velvet Mite. I'm not sure what is happening with this chrysalis, as 19 days later nothing has emerged and whilst it has a dark mark on one side, it doesn't show the tell-tale signs that it has been parasitised by Chalcid wasps. Maybe the other kind of wasp will hatch out of it!

Another chysalis in the same pot - still waiting to see what happens to it!
But I don't think there's a butterfly forming inside.

And here's the 4th one I found which also has a Chalcid wasp on it, and some days later
as you can see on the right, part of the body of the chrysalis turned a strange brown colour.
Since I took this photo it also shows the tell-tale signs that it's been parasitised by a Chalcid wasp.

And what are these markings? I got this info from this very interesting site which although it is talking about Black Swallowtails, they have very similar chrysalises and I could see the same thing happening to this species. It's the dark markings that you see below, and far less obvious, a change in the shape of the lower abdomen. Far more info about this in the link above.

The membrane between these segments turns darker
which is the giveaway that it's been parasitised.

Because I keep an eye on them regularly I was lucky to get to watch some of the little wasps hatch out of the first chrysalis!

Left: A Chalcid wasp is actually stuck in the exit hole!
However the wasps had made another hole on the other side.

Here's one just emerging.

Still emerging but note that sticky stuff in the right hand picture.

The poor thing got stuck - seemed its leg was stuck on
the remnants of the sticky stuff I mentioned above.
I was kind and got a blade of grass and helped it off!

So out of four chrysalises, one got eaten by ants, two were parasitised by Chalcid wasps and the last one I'm still waiting to see what happens, but I don't think a butterfly is going to emerge as it's well over due and I haven't seen any signs of life from the chrysalis. They will often twitch if you breath on them or tickle them with something like a blade of grass. A bit of a shame as I'd hoped to be able to say "ta-da, here's one that made it", against all the odds. But the other day whilst doing some deadheading guess what I found in the Valerian that had flopped over into the grass? It certainly doesn't look like any parasites emerged.....

Hopefully an adult Papilio machaon managed to eclose. It certainly looks like it although
I also note brown markings between the segments. I hope this is just staining from
the pupal fluid that is expelled upon eclosion.

I do appreciate that all that I've documented above is quite normal in the insect world. Numbers have to be kept in check and predation and parasitism is common place. It's just a real eye-opener when you get to witness it all first hand and now makes me want to cheer for every adult butterfly that I see as I know so many didn't make it! 

As for my indoor raised Swallowtails, out of a total of 42, two failed to eclose and one sustained a wing injury whilst wildly flapping prior to putting it outside, so it had to be put down. So I've released 39 healthy adults into the wild but have yet to see signs of any having returned to lay eggs here - probably a good thing as I don't want to be tempted any more! But it has been a great learning curve to also study what happens to them in real life and note how different it is when they are raised indoors with no predators and seemingly, no disease either.

It's been a wonderful experience and I've learned tons more about them this year but I'm not planning on raising them every year. I'm still searching in the stinging nettles in the hope of finding some caterpillars belonging to one of the more common species - here's hoping I'll find some one day!

19 comments:

  1. Amazing work Chateau Moorhen! Great job with the photos and the blog.
    Sad to see the beautiful butterfly devoured but tis the way of the world eh?

    Love seeing and reading about all the wonders of the farm...

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    1. Thanks very much April! Yes that is nature in all its grisly glory. But I've had loads of beautiful indoor raised butterflies to release so I got the pleasure of that. :-)

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  2. Beautifully documented and superb supporting photos once again. This is nature in the raw and a great example of why butterflies (and most other insects) lay so many eggs. Nature kind of...allows for the inevitable and ensures at least some will survive. Gruesome? Yes, I suppose, in a way but I would find it a real treat to witness in my own garden, as you rightly say, there's so much to be learned from observing...

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    1. Hi JJ and thank you. I do appreciate that is how nature operates and isn't different for birds, mammals, reptiles etc either. The gruesome warning wasn't for the likes of you ;-) but I know there are squeamish people out there so no-one can complain if I warn them in advance. :-) I have also experienced Large Whites parasitised by Braconid Wasps (the ones that burst out of the skin of the living caterpillar) and then their hyper-parasitism by Ichneumons but I never put that on my blog as at the time I thought it was too gruesome. I might have to find those photos and post them now. :-))))

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  3. Fascinating post Mandy and those pics of the wasp emerging are superb- well done indeed on getting those.
    You raise an interesting point in noting the comparisons of survival rates between indoor and outdoor raised flutters. The simple response is to think how wonderful that all those indoor flutters survived, and how sad so many outdoor ones were lost, but nature does things the way she does for purposes of balance (I know you know this already) so I think you're wise not to do it every year. Fascinating project - I've enjoyed following your documentation of it.

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    1. Thanks very much CT! You could say that the butterflies I've released wouldn't make that much difference but if many other people were doing the same it could really upset the balance of nature so I know exactly what you mean. :-)
      I'll catch up with your blog tomorrow as I've been a bit busy this week and hardly had time to blog myself.

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  4. Brilliant stuff Mandy.I've been looking on the nettles the other side of our wall and like you, nothing. Found zilch in the garden but as there's no veg I don't know which flower plants in the garden (if any) might be host plants. I need to research a lot if I wanted find wild plants with caterpillars. I was really lucky with the Burnets. I may just read your blog instead :-)

    Great photos as per usual Madame.

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    1. Thanks Nick! Nasturtiums are a good one for Large and Small White (I'm not sure about Green Veined) in the absence of any brassica veggies. I have already flicked off loads of Small White eggs from my winter brassicas which are still in the cold frame! Finding nothing on nettles really bugs me because so many common species like Peacocks, Red Admirals, Commas and Small Tortoiseshells lay their eggs on them so I ought to find some. Maybe I'm just not looking in the right place; have so many nettles here dotted about I can't check them all. :-)

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  5. That is amazing documentation, Mandy! You have been very busy keeping check on all those caterpillars and their various stages.
    I can't believe you had 42 in total. I would never find that many in my little garden.
    Great photos and thanks so much for sharing what you observed!

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    1. Thank you Kim! It was an amazing season for these butterflies (and me!) as I'd never discovered their eggs before so that made it all the more special, to see the process all the way through. There were loads of caterpillars outside too so chances are quite a few of them made it to adulthood. I'm glad you enjoyed seeing and reading all my posts about them. :-)

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  6. Just catching up on your posts( had a little time out) stunning Butterflies in your last post and this one is very interesting, you have done so well to capture these events with great photos..
    Amanda xxx

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    1. Hi Amanda and thanks for the great comment. Hope you had fun during your time out! :-) xx

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  7. Replies
    1. Oh dear Caked Crusader, I hope this post didn't put you off your cake! ;-) Thanks for visiting, that was very sweet of you.

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  8. OK copy before publish :P
    high drama in the world of crawlies Mandy , thanx for the chronicle :))
    tag me if there are developments

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    1. ah ha success! after a couple of tries

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    2. seems once it knows me on a post it publishes ,

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    3. and i didn't even have to scroll back down to the end of comments this time :)))

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    4. It works!! Well done my dear and thanks for taking the time to comment. Nothing else happened actually - the one that started turning brown went very brown, hollow looking and wrinkled like there is nothing inside it (but no exit holes) and the other one just sits there looking green and firm but no exit holes either - maybe it just died but wasn't parasitised? Bit of a shame really. :-)

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