What’s the monarch’s favorite milkweed?

Swamp milkweed (Asclepias incarnata)
Credit: Jardin botanique de Montréal (Stéphane Bailleul)
Swamp milkweed (Asclepias incarnata)
  • Swamp milkweed (Asclepias incarnata)
  • Butterfly milkweed (Asclepias tuberosa)
  • Common milkweed (Asclepias incarnata)
  • Poke milkweed (Asclepias exaltata)
What’s the monarch’s favorite milkweed?

In North America there are over 90 species of milkweed, four of which are native to Québec. Are monarch butterfly females more attracted by certain milkweed species when it comes to laying their eggs? Researchers conducted two experiments to answer that question.

A laying closely observed

In a first study, the scientists tried to determine whether females distribute their eggs differently depending on whether they have a choice of milkweed species. The monarchs were released in breeding cages where different species of milkweed had been positioned. In certain cages the species were isolated: i.e., there was only one species per cage. In the others, four species were available.

Comparing the number of eggs laid on the plants, the researchers found no difference among the species of milkweed when they were isolated. However, when the monarchs had a choice, they laid more on common milkweed (Asclepias syriaca) and swamp milkweed (Asclepias incarnata), both of them native to Québec and Ontario. Moreover, they laid more eggs in cages containing four species as compared to the single-species cages. These results show that monarchs can be satisfied with a number of different milkweed species, but nevertheless have preferences when given the possibility of choosing their host plant.

In nature

Laboratory experiments are very interesting, but what happens in nature? To find out, the same researchers repeated their study outdoors. The results confirmed those of the initial experiment: common milkweed and swamp milkweed once again presented the greatest number of eggs.

And in your garden?

This research is useful to us in terms of organizing oases for monarchs. Think about planting these two species of milkweed – but you don’t have to stop there! Females lay more in the presence of several milkweed species. And what’s more, butterflies need a diversity of nectar-producing plants to feed themselves throughout the summer. You’ll find all the details about oases if you visit this page. Finally, share your observations of milkweed and monarchs via the Mission Monarch site!

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