Searching for Signs of Monarch Butterfly Breeding

Along with tagging monarch butterflies to study their migration paths, in my internship I am also conducting field surveys for milkweed, monarch butterfly eggs, and monarch caterpillars. I send my data to both the Southwest Monarch Study and the US Fish and Wildlife Service. USFWS is currently using data to decide whether monarchs need to be listed under the Endangered Species Act. My work is important because little is known about monarchs in the Uintah Basin area around Dinosaur National Monument. We need to know where monarch breeding habitat is if we want to protect it and conserve monarchs.

In my early days of the internship, finding monarch eggs was pretty tricky. I had no experience with them and I just knew they would be tiny little things on milkweed leaves. Like most other people I have met, I got pretty overwhelmed when I realized that milkweed plants have all sorts of little things on the bottom of their leaves. Usually, these are little injuries or scars or maybe just dried globs of milk. Luckily enough for me, telling a monarch egg apart from all these little distractions isn’t too tough once you really know what an egg is.

A monarch egg is sort of a yellow to creamy color. It almost always will be underneath a milkweed leaf, though I’ve found a few on the top sides. The egg is also a regular shape, there’s not all these little bubbles and weird geometries to it like there are in dried milk globs. If you look closely, you’ll see that the egg ends in a little point and it has little ridges all along it leading up to that point. Usually, I find just one egg per milkweed plant, but sometimes there will be a few eggs on a single leaf.

After a few days, those monarch eggs hatch into caterpillars (larvae if you want to sound scientific). Upon hatching, a monarch larva takes about 2 weeks to eat lots of milkweed leaves and mature through 5 larval stages, called instars. Larvae molt in between instars and after their fifth stage, they go into a chrysalis for metamorphosis. The first instar, right out of the egg, is only about 1 millimeter long and has very little color. If you find one, you’ll probably see that it’s already made some chew marks in the milkweed and maybe has caused a little milk to start spilling out of the leaf. A first instar larva is pale and doesn’t have any tentacles at its head or rear. By the fifth instar, the larva is up to 45 millimeters long, with big tentacles and bright yellow/black/white coloration. Whereas you have to closely look at the underside of a leaf to find a first or second instar larvae, the third to fifth instars can be spotted from a little farther away. They also are sometimes on the milkweed stems rather than under the leaves.

It is not for the faint of heart to survey a whole patch of milkweed for an hour or two. You’re bending down and standing up, most everything is so tiny that it’s hard to get a camera to focus for a picture, and you’re always stepping carefully to avoid trampling a milkweed plant that might be housing a precious baby monarch. If you’re working in Dinosaur, it might also be 95 degrees under a completely cloudless sky.

Nevertheless, finding each new egg or larva is always cool. I’m reminded of this every time I show a Dinosaur visitor a monarch egg or larva and they get all excited, calling over family members to have a look too. If you find milkweed somewhere, have a look around to see if you can spot any of your own monarch eggs or larvae. If you find any, you’ll have evidence that monarch butterflies are using and breeding in that habitat. If you don’t, you still at least will have opened your eyes to all the biodiversity living in the microhabitat of milkweed plants. You’ll be amazed at all the insects and things you never thought about but see once you start looking closely at plants.

If you need a little help finding and identifying monarch eggs and larvae, have a look at this video or this guide from the University of Minnesota. I highly recommend the video, whose creators have managed to capture high quality images of tiny baby monarchs.

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