Swan plant is too toxic?

This topic contains 3 replies, has 2 voices, and was last updated by  Jacqui 3 years, 8 months ago.

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  • #46888


    I recently bought some new young swan plants to boost food supplies for my caterpillars. I transferred some caterpillars to one of the plants soon after getting home, and now two days later all the caterpillars on that plant are not eating, very still, and I think dying (no discharge or green goop).

    I rang the store and they said the plants are definitely not sprayed, and indeed even had a few little babies on them. I have read that the toxicity levels of plants can vary and that’s why you shouldn’t transfer caterpillars (let them move in their own time) and I wonder if that’s what’s happened (there is no evidence of any of the other usual suspects). However, this has never happened before, even though this is my usual practice.

    If this could be the case, my questions are:
    * how does the toxicity level come down? Is it just a matter of time? Of watering them? where does the heightened levels of toxicity come from? I don’t plant my swan plants, but leave them in pots so i can move them into a netted area and bring them out sometimes for sun baths etc. Will the toxicity level be able to come down or is it a soil thing?

    * how come the little caterpillars already existing on the new swan plants are unaffected?

    * Is there anything I can do for my caterpillars that have ingested this swan plant toxin?

    * when IS it safe to transfer them? I prefer to do this than let them starve on (and completely strip) a plant and then have to traverse the pot and deck to find a new plant.

    Ugh so disappointed this has happened!

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  • #46904


    Willis, I don’t think anyone has done any detailed testing of the plants to measure the toxicity – and then the same plants grown in different conditions would affect this.

    And then again it COULD be spray drift in the garden centre, or when you took the plants to your car at the garden centre or even from your neighbour’s gardens. There are too many unknowns to be able to put your finger on it.

    Personally, I would just leave the caterpillars to do their thing. I understand that you don’t want them dying, of course, but a lot of the knowledge that comes with raising monarchs comes from experiences.

    I’m sorry, this is all not very helpful! Hopefully someone else may have some better suggestions.




    Thanks Jacqui. Can you help me understand how the toxicity of a new plant comes down to a similar level as my existing plants? Is it to do with time, watering, soil? I’m gun shy now after having looked after my caterpillars so well and with such a low death rate, to have this happen. I am nearly out of leaves from my old plants so need the new ones. When can I have confidence in new plants? And why don’t the caterpillars leave the too toxic plant and go to a safe one?

    If you have run out of leaves, is is better to let the caterpillars not eat for a day or two, rather than give them a new plant that hasn’t ‘adjusted’?

    I always transfer the caterpillars by encouraging them to walk from one leaf to another – I don’t touch them, so it is definitely the plants.

    Thanks for your time Jacqui – this is one area I’m having trouble understanding well enough to make good decisions.



    Hi Willis008 – that’s correct, different types of milkweed can have different levels of toxicity. Even the same plant grown in different soils and with different water content in the soil could have different levels of toxicity.

    Always let the caterpillars transfer themselves, and water new plants well. There are two reasons for this: THEY will know when they should be eating the new plants. You’re almost “force feeding” them. Just put the new plant alongside the old plant, and water them both well. There is also the possibility that your hands might have something on them that the caterpillars object too. Soap residue and sunscreen comes to mind… easily overlooked.

    Check out “Feeding monarch larvae” here.


    Sorry to hear that you’ve been having problems. It is very difficult knowing whether plants have been sprayed or not. It is much better to grow your own, to not get too upset if wasps and other predators take some of the caterpillars, and to enjoy those that do make it to become butterflies.

    A plague of monarchs


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