Desperately Seeking Monarch Butterfly Eggs and Caterpillars: Where and How to Find Them

Thumbnail image for monarchinfrontyard.jpgAs the Monarch butterfly migration gains momentum, their increased numbers make it easier to spot the elusive creatures as they move through San Antonio on their amazing multi-generational migration. Scientists have long asserted that a “Methuseleh” generation of Monarch butterflies migrates. The theory is that the migrating generation, which can live up to nine months, doesn’t lay eggs or mate on its migrational route in order to conserve energy to make the 3,000 mile journey to the Monarch butterfly roosting spot in the mountains of Michoacan, Mexico.

Yet those of us paying attention to Monarch butterflies during the migration season have witnessed their reproductive dance on more than one occasion. And we regularly find eggs and caterpillars this time of year right here in San Antonio and the Texas Hill Country.

The offspring of these South Texas-born Monarch butterflies have an excellent chance of completing their journey, since they have “fresh wings,” and won’t be as tired or ragged as their butterfly brethren who may have begun the trip as far north as Canada.

So how do you find Monarch butterfly eggs and caterpillars?


Look on the underside of the leaves of almost any member of the milkweed family. If you see a female Monarch lighting on milkweed, gently tucking her rearend onto a leaf, make an inspection once she flies away and you’ll often find a creamy yellow oblong dot, no bigger than the head of a pin. It’s a future Monarch caterpillar.

In San Antonio and Austin, you most likely will find them on Asclepias tuberosa or Asclepias curassavica, two common milkweed plants sold in nurseries. If you’re lucky enough to have Asclepias asperula, also known as antelope horns, in your neighborhood, check there as well.

For everything you ever wanted to know about milkweed, see the Monarch Watch milkweed page, which includes photos for easy identification.

When scouting baby Monarch caterpillars, look for little holes in the leaves of plants. When you flip the leaf, you’ll often find a caterpillar hiding and munching.

The first thing a Monarch caterpillar eats upon hatching is her egg shell. Next, she begins consuming the surrounding leaf. This often results in an obvious hole, a clear sign that a caterpillar is present.

Just remember that if you retrieve Monarch butterfly eggs or caterpillars from their natural setting, you are obliged to provide food. That means having plenty of healthy milkweed on hand. Monarch caterpillars will ONLY eat milkweed leaves, and they generally consume 200 times their weight in foliage. That’s a lot of milkweed.

If you have milkweed plants in your yard, you can monitor the caterpillars’ progress there, but be forewarned. In the wild, only 10 percent generally make it to the butterfly stage. Female Monarchs lay an average of 400 eggs, and unfortunately 90 percent of them never become butterflies because of predators, disease and other threats. Interestingly, the odds are reversed when you bring the eggs and caterpillars inside and help them along. We’ll cover the dangerous world of butterflies in a future post.

In the meantime, you can do your part by planting more milkweed.

Monika Maeckle