Mystery Cocoons

Do you know what these are? Or what made them?

Prior to 2020 I had never seen anything like them. These capsules are produced on the bodies of dead butterflies, presumably by some kind of tiny detritovore. I find them to be beautiful; the capsules themselves are iridescent in the green to purple range and each one is uniquely adorned by tiny chewed up pieces of the butterfly’s scales. I keep coming back to them but I’m no closer to identifying them. If you recognize them, or if you know somebody who might like to take a crack at it, please drop me a line.

  • Collected in summer 2019 in Frontenac county, Ontario, along the side of a highway.
  • These butterflies were all roadkills, some with some weathering.
  • The cocoons/capsules are approximately 300-400 microns in length, not counting the membrane tab, with some being slightly smaller.
  • Species I’ve examined that are affected by these cocoons include Monarch, White Admiral, Question Mark and Painted Lady.
  • The cocoons are most richly deposited around the thorax, with some nestled in along wing veins, and others appearing in surprising locations such as being attached to a leg, suggesting they may be made by a detritovore well after the butterfly died.
  • The types and colours of scales used to adorn the capsules are not always to be found close to the location of the capsule, suggesting the critters that built these may be quite mobile.
  • The colours of both the capsules and the mosaic surface layer vary greatly, the latter influenced by the types and colours of scales selected. I don’t know what causes the varied iridescence of some of the capsule walls. Most have a blue cast, while a few are green or purple. Perhaps the critter produces some kind of paste from butterflies scales it consumes for the purpose.

I recently found myself reviewing old specimens I’ve collected over the past few summers. In August 2020 I collected an abundance of Sulfur butterflies. They’re very common here among the farm fields and the traffic absolutely hammers them. I collected at least a hundred of them during an evening walk. I took some photos and bottled the rest, and on my shelf they’ve sat until this week. I poured them out onto a sheet of paper to take a closer look and I saw what looked like fine dust in the bottom of the jar. I figured they were shed scales or perhaps debris from something consuming the butterflies, as can happen in dried collections.

I tipped some onto a slide to take a look and I was blown away to find hundreds, perhaps thousands of the tiny, bejeweled capsules that I’ve failed to identify since I first spotted them in 2020. Those were from specimens I collected in 2019 in Frontenac County, ON, near the town of Ardoch. I think they must have been “contaminated” by my other specimens because I never found any sign of these capsules at any other location. I think they then exploded in population in the bottle and produced these structures.

Most importantly, I now have a suspect for what may have manufactured the capsules. There were numerous examples of the critters pictured below in the bottle with the Sulfurs and the capsules. Strangely, there are many more capsules than there are bodies, leading me to wonder if the bodies I’ve found may be a different critter that consumed the capsule creators. I’m wildly speculating. I have no idea what made these capsules or what the identity of the insect below may be. I’d really love to put a name to these things so if you recognize them, please drop me a line at, use the provided Contact Page, or, if you know somebody who might recognize them, please forward them the link to this page.

This next set is from a monarch butterfly.

And some more stacks. Each is clickable for the full sized image.