Garden Centre Swan Plants killing Monarch caterpillars

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  • #12813


    I have only just joined this site and have found the information here invaluable. This year I have successfully raised and released over 80 monarchs by transferring them from the plants down my driveway to the house for protection. Unfortunately they had nearly stripped the plants so I purchased a large healthy Swan Plant from Kings Garden Centre. This has resulted in many of the caterpillars dying. I can not find out from Kings if the plants were sprayed and if this is the problem. Has anyone else had this problem?

    Cheers Joy

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    This year I have been happier with the health of plants offered by garden centres, however I always wash any plant before offering them to my caterpillars. Caterpillars are very sensitive to anything foreign on their food source – even if you handle the plants while wearing perfume, or have an air freshner in the car while the plants are being transported, it can affect them.

    I bought some plants off an “organic” grower which I washed (as always), however the plants must’ve still had something on them because the caterpillars threw themselves off and writhed. I removed the offending plants straightaway, kept them in a nice spot and hosed them EVERY day for THREE weeks. I tried them back with my caterpillars yesterday with almost disastrous results. I got to the caterpillars in time, thankfully, but have thrown the plants away. Caterpillars will vomit (exude green fluid) when they are disturbed or threatened. This regurgitation can also help get poisoned material out of their systems. The vomit can look dark on the plants.




    We have had so much interest in the butterflies over the past few days. I just received another email from a woman in Raumati (near Wellington) who had originally said:

    >> We read todays newspaper article with interest.

    >> We live in Raumati and are blessed to have 7 plump caterpillars feeding happily on a swan plant, which we are nuturing with interest. They have already munched thru one plant we had grown and had to make a mercy dash to the nearest plant shop for a new plant.

    >> My 8 year old son Harrison and daughter Sophia (3) are fascinated and regularly check on their friends. None of us know the exact time it will take for the metamorphesis to take place so we all await with interest.

    >> One thing we have noticed is that since we introduced the new plant they don’t seem to eat as fast and almost have diahrea, or should a say a trail of black liquid behind them. Is this normal? We wondered if there may have been chemicals used on the purchased plant causing this to happen.

    >> We are really enjoying our little touch with nature and making the garden prettier, and hopefully soon will experience and explosion of colour.

    Today she wrote back to say:

    We have since given the plant a bit of a light shower with the hose and they do seem a bit happier and have started munching again. One little one seems a bit more poorly but is still moving and eating, just seems slightly shrivelled compared to the others. From time to time they drop to the ground up always managed to retrieve and return to the plant.

    Confirms this water theory!

    One thing — be careful not to move caterpillars too much (by hand). They do wander off the plant to shed their skin – and they are very vulnerable at that time. It’s believed they go away from the plant to escape predators. They will soon find their way back again. (They go through four-five stages or instars as they grow. They actually grow 3000 times in size!)



    Thanks for this Dean.

    I seem to recall this – about the plants toxin getting stronger when they’re short of water – it makes sense, doesn’t it! This could be key to Shirl’s problem (see post elsewehre).

    Entomologists have suggested that our milkweed be planted in pots, so that they can be moved away when wasps discover their location. It confuses the wasps, and the caterpillars are safe from predation – until they are rediscovered. So that’s another key – keep them well-watered.

    Thanks for the input.





    Joy and Jacqui
    Thanks for the letters you have posted on the site. It is always a great concern, to us all here at Kings Plant Barn, when we hear of Monarch Caterpillars not surviving. The first thought is always, have the plants been sprayed before they come to the Garden Centre. We are happy to let you all know that ours come from nurseries where they are grown in houses with mesh covers and don’t spray.
    One of our staff at Kings in St Lukes, Heather has been having a simular problem with hers. We feel the cause of the problem may be that with the hot weather we have been encountering in Auckland lately. The plants are drying out and then as they try to survive they secrete a toxen that kills the caterpillars. We feel the best way to prevent this is to ensure a regular watering program is introduced. In areas where the soil is still not holding enough water, there are products availiable that will help with water retention in the soil. All branches stock this and will be happy to help. If they are still in pots we recommend that you plant them out into the Garden.
    Many Thanks



    Sorry to hear that, Joy.

    I would contact Kings as I’m sure they’d be horrified to hear this. We had a lot of this sort of problem last year with many garden centres, and I know they understand that swan plant shouldn’t be sprayed as much of it is used as “feed” for our “babies”.

    However, it’s also important for us to learn to manage our “farms” much better than we do at present, i.e. plant swan plant (milkweed) NOW for next year’s butterflies to lay on. That way we have total control of the quality of food we offer.

    Do talk to the garden centre about your problem – I am sure they will be most upset.


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