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