Two generations of monarchs

This year, we have been planting a lot of milkweed. We wanted to attract monarch butterflies; not the nectar-hungry fall visitors but mothers who look for suitable food for their babies. Monarchs eat nothing but milkweed, and they are on the decline because less and less milkweed  grows along roads and agricultural fields. Gardens can come to the rescue, and we tried to do our part.

Some of our milkweed plants

All summer long, we were looking out for monarchs. Finally, a few weeks ago, they arrived. Most days, we could see a few butterflies hovering over the garden and sipping nectar from zinnias and buddleia.

Monarch on the butterfly bush (Buddleia).

But were they interested in our milkweed? This week, we discovered telltale holes in the leaves of some milkweed plants. Milkweed is very poisonous. Only few specialists can eat it. Among those specialists, only monarch caterpillars chew holes into the leaves. And indeed: on the underside of leaves with fresh holes sat the tiniest monarch caterpillars, unmistakable with their black, white and yellow warning colors.

The turned-over milkweed leaves reveal tiny monarch caterpillars. A first instar larva on the left, a second instar on the right. These babies need to go through 5 larval stages before they are ready to pupate.

These little caterpillars are likely the 4th generation of Monarchs this year, and if they grow up, pupate and metamorphose into butterflies, they will be very special. Different from their parents and grandparents, these monarchs will not mate and lay eggs right away. Instead, they will go on an long journey all the way to Mexico, where they spend the winter in a tree together with thousands of other monarchs. In spring, these butterflies will fly back north to find newly grown milkweed. Then, they will finally mate and lay eggs. Their children will fly further north and may reach New York and Canada. By late August and September, the great-grandchildren of the overwintering monarchs are adult. We think that these are the adults in our garden right now.

There is plenty of milkweed around, the days are warm and still fairly long. Therefore, this generation of monarchs is still reproducing. Two days ago, w could even observe a mating pair. When looking carefully, we also found their small yellowish green eggs on the underside of many milkweed leaves.

Monarchs remain still when they are mating. This pair stayed on the zinnia for at least 10 minutes. (Photo: Ellen Reznick)

A monarch egg is not much larger than a poppy seed. The larva that hatches from this egg is equally tiny.

If it stays warm, it may take just a bit more than a week for the little larvae to be ready to pupate. And in another 10 days, the adult monarchs could emerge. That is, if everything goes well. Even though monarchs are as toxic as their food plants, they still have many enemies who can tolerate the toxins, including ants, wasps and spiders. We cross fingers that some of our baby monarchs survive, become adult and embark on their amazing  journey to Mexico.

More information about monarchs is found on this wonderful website by the University of Minnesota.