Caterpillars "folding", dying.

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  • #14724


    Noticed this morning, three caterpillars dead on their leaves, half hanging from their middles, like a limp sleeve.

    It is as if the caterpillar is half deflated.

    I have also got a couple who look like they are descending into that state, I suspect alas that they are already dead as they are unresponsive to the touch – barely flinching at all – what little there is may just be a reflex – they look otherwise healthy, although they feel a little "softer" than usual. (that’s the only way I can describe it – as if their insides have liquified.)

    They have been transported from a mesh-bagged swan plant outside, so it’s not wasps. The plant did have numerous aphids. It is possible that there was overcrowding on that plant, but subsequently they have been four days on a large, healthy new swanplant indoors, with no aphids.

    (And no, I dont use sprays or have any insect controllers)

    Could it be a spider bite that may have caused this? (I was interested to see a reasonable-sized pale spider with a triangular abdomen, on the leaves when I was transferring them) Or could I have damaged them in handling, during the transfer, and it’s manifesting when they are attempting to shed their skin? Most of the affected caterpillars appear to be just over an inch long.

    I have not seen any sign of a spider on the plant indoors, but I am keeping a close watch.

    On the bright side though, I have around 21 chrysalises, and if the other caterpillars don’t suffer the fate of the above ones, I can hope for nearly another 20 more!

    Jacqui: on the nettle growing front, I’ve now got around 12 mini-pots with tiny shoots that are slowly getting bigger. They’re probably too teeny tiny to be of use to you yet (about a centimetre tall!), and there seems to be a top-soil fungus on one of the pots which I’ve tried to quarantine, but two others are showing signs of it. The seedlings don’t seem to be affected by it though. :)

Viewing 16 replies - 1 through 16 (of 16 total)
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  • #53695


    Charlotte, I had my caterpillars die at the beginning of last season, they just stopped eating one after another and just sat there, they were getting darker until a they died with a black liquid coming out of them which I thought it is there blood. I’m pretty sure now after reading your NPV symptions that that is what it was. I just thought it was strange how they stopped eating basically one after the other but makes sense since it is catchy. I only had a couple from that lot make it to butterfly as the others I must of moved to a different plant in time. The next lot of caterpillars I had from then all turned out fine. They were all raised outside in the garden.



    Hi szyjkak – it does sound like it’s dead or dying, I’m afraid to say. There are many reasons why this could be so.

    Hope the rest of your season goes better!




    My caterpillar was healthy, fat and happy and I put the milkweed branch in water and it was hanging on to the underside of the leaf. Had it in the car…by the next day it was no longer hanging on at the end, but in the middle of its body where it started to get black and it looks lifeless. Has it died?



    Hi Serra

    Probably not necessary – I would plant the plants out and cover them with a net so that the Monarchs can’t find them – or try this, mash up some strong-smelling leaves in a vitamiser (or something) with water, and spray or somehow drench the plants with those – what you’re trying to do it make them smell NOT like a milkweed, so that the butterflies don’t find them. Then you should have great plants for next year. Plant them somewhere warm and sheltered from the wind.

    Hope that helps!




    Thanks Jacqui. I am at Paraparaumu Beach / Kapiti Coast, though I work in Lower Hutt Wellington . Should I get rid of the plants that might have been sprayed? I cant really save them can I



    Hello Serra

    Sounds like the plant(s) have been sprayed. 🙁

    Whereabouts are you? I could probably put you in touch with someone who has unsprayed plants nearby. You can ring me on 09 551 3383 or 027 481 4811. I am in Blockhouse Bay, Auckland.

    Get in touch as soon as you can and we’ll see what we can do for you.




    Hi I am new here, and new to raising cats!


    I had two very healthy looking cats that devoured my swan plant, so one night on a mercy mission for more food I went to pak n save for pumpkin and saw they had swan plants. Delighted I bought two and transferred my cats which were over an inch long by that stage. Within a day both were lethargic and then lifeless and ended up in that upside down V which I have since read about on here


    I am guessing something is wrong with the plants I bought. Can I try and save the plants somehow or should I start over? There are two teeny tiny cats about now…





    I had a caterpillar die in a similar fashion to the one you described last year and it was after a long fight with another and one of its front filaments got torn off. Mine was a big caterpillar.



    I remember reading at one point, that in conditions of stress, certain soil conditions etc, the plant itself may become more toxic? Is this speculation or a possibility?

    Speculation as far as I know. Cardenolide levels vary wildly between different species of host plant, different plants in the same species, different parts of the same plant, and at different times in the same plant.

    I had a caterpillar die a couple of months ago in an unusual fashion. It was in a castle with 4 others which I had on display at a local preschool. The other four were apparently fine, but the fifth turned black and rigid, like a twig. I’ve never seen that before. I make sure I soak my castles in bleach and rinse before using them again, but I can’t rule out some strange microbe landing on one of the leaves.

    In an ideal world I’d build a butterfly and aphid proof enclosure, kill everything inside, and then grow my milkweeds in there. But the sad reality is that monarchs lay hundreds of eggs when only two are needed.

    Big bugs have little bugs
    upon their backs to bite them.
    The little bugs have smaller bugs,
    and so on ad infinitum.



    I too have the ‘folding’ disease, but mine are doing it when they are about the size to go into a chrysalis. The tree from last year became host to so many aphids it succumbed so I pulled it out and let a new one grow up which this last batch of caterpillars are living on. I have had 3 successfully go to chrysalis stage so am not sure whether to pull the whole young plant out or just hope that new growth won’t be affected and it will be ok for the next season.



    That sounds a lot more like it, Norm!

    I did wonder earlier if the bacteria could have been present in the potting mix (given that potting mix usually comes with a warning label about handling it, for the very reasons of bacteria sometimes propagating in the soil.)

    Some of these catties have been in contact with that.

    There were no casualties this morning, and the sickly four are still alive, albeit sluggish. Still producing frass.
    They still seem quite responsive to “gusts of fresh air”

    I’m hoping that the good solid watering, with the addition of a drop or two plant nutrient, has arrested any further cases.

    I do not know if the catties will get over their lethargic state or not. it will be interesting to see how the larger ones still on the plant will fare, at the chrysalis stage. That will be an indicator of whether or not they have also been affected.

    And it seems that Bt is the closest match to what may be going on, so thanks for that information. 🙂



    Hi Kirby,

    Some good observations from you, and the fact that the smaller caterpillars only are affected is interesting, and although toxins could be a suspect, a poisoned caterpillar reacts by dropping from the plant and writhing on the ground. The fact of them hanging in an inverted V is typical of a viral disease such as NPV but the skin ruptures and the contents discharge, the disease spreads rapidly as Char mentions, plus the larger caterpillars would become infected also. There is a bacterial disease (Bt)that causes the caterpillar to “become lethargic and stop feeding, darken in colour and soften, but the integument (skin) remains intact”. The disease is soil borne and is also produced as the most widely used bacterium for pest-insect control in agriculture. But it “does not normally cause serious disease outbreaks in insectary settings”. Could your plants have been subject to any wind borne spray? The residue on the leaves sounds a little suspicious.
    The progress or demise of the larger caterpillars should perhaps pinpoint the problem further. The caterpillar needs to ingest the virus/bacterium to be infected so your chrysalises should be OK.
    Keep us posted.



    Thanks for the information on that, Norm and Flutterbys!
    More rambling updates follow:

    Had three more “poorly” catties this morning – one dead, two questionable.

    I have noticed, looking at the plant in general, that it seems to be being eaten rather patchily – as if the caterpillars have tried a bit of leaf and gone “nope” – rather than eating the whole leaf as would be usually expected.

    There is a very light fungal residue on some of the leaves, I have since discovered – from water that has dried out on the leaf. (I double checked back with Kings Garden Centre, re. spraying, and the chap informed me that this was what it appeared to be, comparing it with plants there. He reassured though that there had been no sprayiing.)
    I’m sure I’ve seen this kind of residue before, in any case, and it didn’t harm catties then.

    So far, it doesn’t seem to be affecting any of the larger catties – only the roughly inch long ones. Ones of a slightly larger size that seem to have been similarly affected, are a little more responsive. I’m not sure if they’ll recover, but they do move around when left to their own devices, in the box I’ve placed them in. I have brought in leaf from an outside plant.

    Going through the NPV checklist –

    1. Smell. The main smell seems to be the plant itself (there are a lot of blossoms, and it was almost overpowering when I first brought it home!) – but then again, it’s freestanding inside, not enclosed. Light vegetative smell is all I’m picking up on at the moment.’

    2. The plant does seem to be being consumed rather patchily of late – the leaves are not being eaten fully – in many places, leaves look like they’ve only been “lightly sampled”, with small holes here and there.

    3. Not much diarhhea – even some of the sickening ones still appear to expell frass, although I have noticed some small spots of diarhhea. (This could also be vomit)

    4. Sluggish – yes. Responsive to breeze though – seems to prompt more activity. I think all of them seem a bit sluggish, including some of the larger ones – although that might be my imagination.

    5. Not noticing ruptures.

    6. Darkening, yes. Translucency (and/or the ‘wet’ look), no.

    7. Inverted V. – partial. Have only noticed a couple in full V – usually the smaller ones.

    8. Liquifaction – not showing external signs of this. A little dehydration, some softness yes, but no “melting”.
    One that seemed a bit soft however, is one of the ones who is still shifting about. There was a little diahhrea on the paper it’s been on (or vomit?) this morning, but it’s not deaded yet.

    I do wonder about the soldier bug – but have not found any – yet! And it’s still only affecting ones of a certain size.

    I remember reading at one point, that in conditions of stress, certain soil conditions etc, the plant itself may become more toxic? Is this speculation or a possibility?

    I was talking to one of the folk at the Kings Garden centre, who mentioned that on his property he had a lot of swan plants, but that the butterflies didn’t seem to be terribly attracted to them. (either that, or he’s also got wasps picking off any caterpillars ;D )

    A larger caterpillar may have more resistance to a higher toxicity – as mentioned, it’s not affecting the bigger ones, and the tiny ones are eating only the surface of leaf – not the “leafstem”.
    Checking some of the leaves, I notice along the central stem of the leaf, it looks like some caterpillar has taken a tiny bite out of it, left a gap, tried again, etc – as if it’s been testing the edibility.

    The only thing that makes this uncertain, is that more than one plant seems to be prompting this – I have separated the plants out a little. The affected caterpillars seem to have been on two of them.

    I have fully hydrated the soil of the potplants, and have put a little nutrient in with the water.

    I really do hope it’s not a virus – although it does seem rather like one – just very selective. If it affects any of the big ones in the next couple of days, I’ll know it’s definitly viral. :/

    It’s like CSI – with caterpillars.
    I have been routinely moving all chrysalises away from the food source, even before this started happening (when some have been forming chrysalises on the leaves) – so I hope they’ll be fine. I’ll shift them even further, just to make certain. There’s been no discolouration evident on any of those.



    HI Kirby,

    I would tend to believe Norm Kirby as he is a very knowledgeable man;-)
    If you cannot find any soldier bugs on the plants then it will be a virus.
    It could be NPV (Nuclear Polyhedrosis virus).
    I have just completed a butterfly disease course and learnt quite a bit from this course.

    Nuclear polyhedrosisvirus (NPV) is a dreaded viral disease experienced in many rearing operations.
    NPV usually causes larvae or pupae to literally ?melt?.
    After an NPV outbreak, you will need to destroy all stock, sanitize everything, and start again.
    Larvae which die from NPV usually climb to a high point,hang by their middle prolegs, and die in an inverted ?V?.

    Signs and Symptoms of NPV
    1. Foul odor; if you have your caterpillars in an enclosed area you will know by the smell.
    2. Loss of appetite; caterpillars normally eat less than normal.
    3. Diarrhea; poohs normally look like liquid.
    4. Sluggish movement; instead of normal movement and behavior, caterpillars begin to move slowly or sit in one spot.
    5. Their skin ruptures easily.
    6. Darker skin; caterpillars darken and their skin often seems translucent.
    7. Hanging in an inverted ?V? upon death; larvae hang in this position from the sides or top of a rearing container.
    8. Death; larvae or pupae die and become liquid. A larva which has died from NPV may lengthen to double its length. It will rupture, spilling its liquid body into a puddle.

    NPV can be transmitted vertically as well as horizontally by contaminated food or other items.
    1 ruptured NPV infected caterpillar contains over 1/4 billion virus particles which can spread throughout your gardens or area that you have your caterpillars.
    This is why you have to throw away all stock and sanitise EVERYTHING (walls, doors, door handles, floors etc) and start again.

    That is if you have the NPV virus Kirby. Could be just a soldier bug.




    Hi Kirby,

    Overcrowding is a typical cause of stress which leads to viral/bacterial infections, which liquify the inside of the caterpillar. The disease is spread to other caterpillars ingesting the disease from leaves contaminated by frass from an infected caterpillar, or from the liquification exuding from the dead caterpillar.
    Another culprit leaving similar deflated bodies is the Soldier bug, a brown bug that sucks the internal fluid from the caterpillar. Search your plants to make sure they are not harbouring any, a search through ‘predators’ on the right hand column should bring up a photo of what to look for.
    Keep us posted on whether any more succumb to the same problem.



    On looking through other posts..
    Swansong mentioned this exact same issue last year – probably around a similar timeframe – the caterpillars match the size and appearance that she was talking about.

    The only thing I think I can rule out is a spray, and I’m keeping a close watch on the other catties.

    Also, I found this topic page:

    (site has pictures that may sadden caterpillar lovers!)

    I quote a partial, from the end of that post, (which had an image of a caterpillar in the state I’ve been describing) here:

    “One sign that monarch larvae could be infected with a pathogen is if they stop eating and hang from the host plant (or side of a container) by their prolegs, with the anterior and posterior ends drooping downwards. Dead larvae and pupae often turn dark brown or black within a few hours of death; this can be a sign of bacterial decay.
    Often times, monarch larvae or pupae die for no apparent reason. This does not mean that a pathogen has killed them; other causes of death could include ingestion of chemical toxins, a wound that became infected by opportunistic bacteria, or thermal stress caused by conditions that are too hot or too cold.”

    It made me think – when there are a lot of caterpillars in close proximity, you can see them reacting violently to each other. (presumeably to ward each other off) – is it possible that one could inadvertantly nick the skin of the other?

    It may well be, that when I was transferring them, they squabbled. (I foolishly didnt think of that – just figured they wouldn’t do each other much harm, being in one container for a little time while the new plant was fetched!

    I am aware also that there are also microbes in potting mix (In which the swanplant sits, yarrr!) – that may also provide explanation, if coupled with an injured cattie.
    If you ever read the warnings on a bag of potting mix, it mentions being mindful of microbes in the soil, and to wash your own hands thoroughly after handling it.

    I’m beginning to wonder if the soil itself contains the (sadly natural!) culprit?

    Thoughts? 🙂

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