Gold spots on Monarch chrysalis

  • Creator
  • #14918


    Ever wondered about those gold spots on the Monarch chrysalis? Lots of people do. In the USA Karen Oberhauser is a leader in her field. She is Director, Monarchs in the Classroom Program; Associate Professor, Department of Fisheries, Wildlife and Conservation Biology, University of Minnesota; President, Monarch Butterfly Sanctuary Foundation. Karen has been studying monarch butterflies since 1984 and works with teachers and pre-college students in Minnesota and throughout the United States using monarchs to teach about biology, conservation, and the process of science.

    She writes:

    "I’ve thought a lot about the gold spots on monarchs. Fred Urquhart first studied these spots in the 1970s. He felt that the spots were involved in the distribution or formation wing scale coloration. However, the experiments that he did involved cauterizing the gold spots on the pupa, and it is possible that this process may have damaged the underlying tissue and affected the color patterns. Interestingly, all Danainae butterflies (monarchs and their relatives) have metallic spots on them. If you ever have a chance to get your hands on the amazing book Milkweed Butterflies: Their Cladistics and Biology by P. R. Ackery and R. I. Vane-Wright (I see that there are some copies available on Amazon), it includes one of my favorite photo plates ever, showing an array of Danainae pupae with silver, copper, and gold spots, or even entire metallic pupae.

    "A group of researchers in Germany did a careful study of the properties of these spots. They are not metallic (so they aren’t really gold), but the cells reflect light like metals do, giving them the appearance of being metallic. Their reflection of light is due to the way that the layers of the pupal integument are arranged in these areas.

    "Here are some hypotheses that people have suggested for the reasons that these pupae have metallic-looking spots (I’m sure others on the list can up with other hypotheses, and possibly ways to test them):

    a) Camouflage: they could reflect colors of the surroundings and break up the shape of the pupa; they might also look like dew droplets.

    b) Warning coloration

    c) Filtering particular wavelengths of light which might be harmful to the developing insect

    d) They might not have any function, but just be the result of something else in the cuticle of the insect."

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  • Author
  • #53579


    I am raising monarchs collected as eggs or first instars for release as adults. In watching the chrysalis form, it seemed to me that the spots that form a semicircle (and probably the rest) begin as openings through which the pupa secretes wastes early in the stage, and liquid droplets congeal into what we see.

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