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Doomed to die! - Danaus plexippus

Doomed to die! - Danaus plexippus
Milkweed Meadow 2 miles east of Westwood, Lassen County, California, USA
August 14, 2017
Size: Body length 31mm
I have 'raised' dozens of monarchs over the years via the milkweed plants that use to grow in my yard. I brought many of the green pupae indoors so the kids could watch them emerge and spread their wings, before releasing them into the sunshine - an altogether fascinating process to behold! Eventually the milkweed plants were eaten into oblivion.

Recently I took my Grandkids to a large milkweed patch (Asclepias speciosa) in the woods where this large and lone caterpillar was found. I brought home the caterpillar and sufficient milkweed foliage, and prepared an aquarium setup for the anticipated pupae and emergence. But little did I know at the time that this monarch caterpillar was already doomed to die!

It fed vigorously on the milkweed for several days, and then stopped eating altogether. I was expecting it to pupate, but it never did. Slowly, it seemed, it died. This had never happened with the many homegrown monarch caterpillars. I suspected parasites; which eventually proved to be true with the emergence of three Tachinid flies; two of which are linked below:

I wonder how much of a roll such parasites are contributing to the decline of the monarch populations that return to their winter sites in California. The following lone monarch pupae, and the parasite that emerged, was found already pre-doomed at the same large milkweed patch: