On 16 March I found this monstrous caterpillar on a nettle leaf inside the admiral caterpillar enclosure. It was at least 4cm long.
It was identified as being the common green garden looper, Chrysodeixis eriosoma, which had been parasitised by a wasp. Vegetable crops attacked include basil, cabbage, celery, Chinese pea, corn, eggplant, green beans, lettuce, mint, parsley, peas, potato, spinach, sweet potato, and tomato. I isolated it to see what would eventuate - I didn't want parasitic wasps anywhere near my caterpillar enclosure!
Twelve days later there must have been somewhere in excess of 700 tiny, black wasps came out of the cocoon! It made my skin crawl looking at such a large number of them milling around. They have taken around 12 days to hatch.
Luckily if they had they managed to remain hidden in my butterfly house there is only one chrysalis left that they could have infected, but in the outdoors, they would have been ready to parasitise the caterpillars of the next generation of butterflies that would have overwintered.
Of course, it was a bald, thin-skinned looper that was attacked. I have never captive raised monarchs, but I have brought in plenty of chrysalises to hatch indoors - particularly at the end of the season when the weather turns bad. I have never seen any that were parasitised. I would have thought the hairs on the admiral caterpillars would have given them some protection, but evidently they do have a major problem with parasitism.
Caterpillars shedding their skin may help to dislodge eggs laid on the outside by parasitic flies - or so I would have thought. I am just thankful that over 75 of my butterflies have hatched successfully and been released (around 50 reds and more than 25 yellows) - just one tail ender to go.
I put the container of parasitic wasps in my freezer. We are working on getting them identified and here are some close-up photos of the dead wasps.
