When raising caterpillars goes wrong

Warning: Two photos in this story might be upsetting to butterfly enthusiasts. To give you a chance to get ready for what you are about to see, or perhaps head back to another story on Frau Zinnie, here's a pretty picture of a monarch that eclosed perfectly and was released in my garden.


Considering all the terrible things that can happen to caterpillars, it makes one have an even greater appreciation for those who do survive. The reason why so many butterfly enthusiasts actively bring caterpillars indoors is because the survival rate of leaving them in the wild is so low. A common statistic for monarchs is that "only one or two butterfly eggs out of 100 live to become adult butterflies."

But sometimes, even with the best intentions, caterpillars just do not survive when brought indoors. Here are some issues that can occur:

Wasps and/or Tachinid fly: After a pair of black swallowtail butterflies failed to emerge from chrysalises over an extended amount of time, I returned home one day to find predatory wasps flying about my bug enclosure. Without knowing, I had brought in caterpillars that were preyed upon by a predatory wasp, which laid eggs inside the caterpillar. When they had entered their chrysalises, the fly larvae killed the caterpillar and mutated into the wasp. (If you are aghast, remember that gardeners often cheer for this fate to befall the much-hated tomato hornworm.)

Bt exposure: (Shown below.) Making sure all the source food for any caterpillar is safe is so incredibly important. As tempting as it may be to harvest milkweed or dill and fennel from a wild source, unless you can guarantee that food source is safe, I would recommend against it. You can do everything right when it comes to care, but if you mistakenly feed them food that was sprayed with Bt (which is considered organic, by the way), it causes their stomachs to rupture and they die. It’s very tragic and upsetting when it does happen.


Random insecticides, pesticides: (Shown below.) This can be from anything you mistakenly touch in your home (think a dog treated with a flea and tick treatment, or cut flowers covered in pesticides from the grocery store) to a neighbor who sprays RoundUp all over his or her property and it drifts over to your side with the wind. I’ve lost a handful of caterpillars to this chemical issue this year who appeared healthy all along but were unable to complete their chrysalis. 



There are other maladies that can occur as well, such as OE and black death. A beneficial reference for me has been The Beautiful Monarch Facebook group, where members share successes and sadness that can occur from raising monarchs. The group is very helpful in providing information on how to successfully raise monarch caterpillars. Read more about The Beautiful Monarch group here.  

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