www.ukbutterflies.co.uk

Good morning

I’d be very grateful if anyone here could tell me what’s happening to this small tortoiseshell chrysalis.

Two days ago I noticed it on the east-facing wall of a house (looking pinker than it is in the warm rising-sun light).

Yesterday (cool storm-cloud light) it had a kind of guy rope attached, but no culprit to be seen. Early this morning nothing seems to have changed.

Just wondering if this is an accidental attachment, or if it has some purpose. I knew the chrysalis might have parasites, but I can't make sense of this at all. I'm only just starting to learn about parasitism in invertebrates, so my knowledge is very limited so far, and this guy rope may be perfectly harmless. Either way, I'd love to know its purpose.

À la perchoine

Hi - it sounds like this pupa was, indeed, parasitised and that the "guy rope" is a thread spun by the parasitic larva as it leaves its host. I think your last shot shows the exit hole. It's now probably wandered off to pupate somewhere (and might still be in the vicinity). The parasite is probably a tachnid fly (such as Sturmia bella).

Cheers,

- Pete

Hi Pagurus, and welcome to UK Butterflies.

This looks like a classic case of parasitism by a tachinid fly. The fly grub has been developing within the body of the caterpillar and has now emerged through the wall of the chrysalis. It has used a silk "rope" to get to the ground and crawled away to pupate in a sheltered spot. The adult fly should emerge in about 12 days time.

More information can be found at the end of this article http://www.ukbutterflies.co.uk/reports_ ... 8tyg7Hb4_w, but there is more detailed research available on-line.

Vince

EDIT: I see Pete has already responded

Pete Eeles wrote:Hi - it sounds like this pupa was, indeed, parasitised and that the "guy rope" is a thread spun by the parasitic larva as it leaves its host. I think your last shot shows the exit hole. It's now probably wandered off to pupate somewhere (and might still be in the vicinity). The parasite is probably a tachnid fly (such as Sturmia bella).
Cheers,
- Pete

Pete,

Many thanks for such a quick reply

I have already begun searching for the tachnid fly pupa, and hope to find it to photograph its emergence.

But fate had offered me a substitute for my lost butterfly. Just inches away, on some marjoram, is another pupa, and such delicate needlework!. I have no idea what it is yet, but I hope to be there to witness a healthy emergence. Whatever it is, I won’t be disappointed

À la perchoine

Vince Massimo wrote:Hi Pagurus, and welcome to UK Butterflies.

This looks like a classic case of parasitism by a tachinid fly. The fly grub has been developing within the body of the caterpillar and has now emerged through the wall of the chrysalis. It has used a silk "rope" to get to the ground and crawled away to pupate in a sheltered spot. The adult fly should emerge in about 12 days time.

More information can be found at the end of this article http://www.ukbutterflies.co.uk/reports_ ... 8tyg7Hb4_w, but there is more detailed research available on-line.

Vince

EDIT: I see Pete has already responded

Thank you very much for the welcome, Vince

It’s lovely to have an answer, but I’m still a bit mystified as I thought there would just be a very visible hole, but it looks more like a blob of brown glue. Unless the hole in question is the big split where I thought the butterfly was going to emerge from?. I somehow imagined it boring a hole straight out of the side. (Must read a lot more about parasitism)

Did it leave a blob of silk as a rope attachment? And the silk rope didn’t reach the ground (about 2’ away), but was attached at an angle to the wall just a short distance away, and stretched very tightly.

I keep trying to visualise how (or why) the tachnid fly larvae could have got out and sealed the hole behind it. And also how it could have attached the ‘rope’ to the wall (unless it did a spider thing and just let it drift until it stuck to something, the rope tightening up later as it dried?).

It’s all very fascinating.

I know the other pupa I've found is far too big to be a fly pupa, but I'm hoping to find the other one too. Do fly pupae show any changes before the emergence?

Thank you so much for the marvelous link. In every way it’s the best butterfly ID page I’ve ever seen. If you ever decide to write a book in that format, I will definitely buy it . I must apologise for not locating it before. If I had seen your photo (Small Tortoiseshell (parasitised pupa) Caterham, Surrey) that would have given me my answer

You and Dave got me thinking about whether I’d seen that kind of tachnid fly before. I went back through my files and found these two flies from three years ago (before I learned never to photograph shiny things in bright sunshine ).

I tried to ID them, but the patterns seem very variable, so I’m not sure. Would these two be the kind to prey on butterflies?

The one that was hanging around a bunch of peacock larvae looks very guilty (A better shot of him is below).

À la perchoine

Hi Pagurus,

In my experience the parasitic grub just pushes its way through the outer shell of the butterfly pupa, leaving a gash or flap. The internal fluids of the chrysalis then sometimes ooze out and re-seal the hole. The grub spins or secretes a strand of silk from which it dangles until it reaches the ground (or sometimes it just drops when it reaches the end of the line). I'm sure there are some gruesome clips on U-Tube which show this behaviour.

As far as I'm aware, the puparia of flies do not show obvious colour changes prior to the emergence of the adult.

I am not an expert on parasitic flies, but Sturmia bella looks a good candidate for your mystery fly from the past.

Vince

Hi Vince,

Thank you so much for all the good information.

Once I'm sure that the pupa is completely empty of all occupants I'll dissect it and take a look at it under my microscope. I'm now thinking of buying that DSLR microscope adapter that's been on my wish list for too long

I still haven't found any pupae, but I'm not giving up the hunt. I'm assuming that it won't have gone far as it will want to conserve energy for the next transition. If I find any I just hope that the emergence takes a long time, and that I'm there to photograph it. I hope it's not a nocturnal event (must find out more about the life cycle of Sturmia Bella).

As for the gruesome clips on YouTube, I will follow your advice. I'm quite happy to watch instances of parasitism since no cruel intent is ever intended where animals are concerned. I'm a bit strange like that. The only thing that I find gruesome in life is what humans inflict on other lifeforms, including themselves. However, I don't necessarily like to watch everything that's natural

I agree with you that the fly looks very like Sturmia Bella, but I'm not sure that both flies are the same. I know that visual ID's of flies can be a nightmare, but I do have a friend who's an expert on that family, and I haven't written to him in far too long.

Once again, many thanks for taking the time to enlighten me

À la perchoine