|MadSci Network: Zoology|
Hi Celeste, Are there any caterpillars that feed on milkweeds other than monarchs? Great question! There is actually a whole group of related Lepidoptera (the Order containing butterflies and moths) known as milkweed butterflies (a subfamily, Danainae, in the family Nymphalidae), which includes about 300 different species that feed on milkweeds! However, only four of these species are found in North America, the most well known being the monarch (Danaus plexipus). The other three North American species are known as the Queen (Danaus gilippus), the Tropical Milkweed Butterfly (Lycorea cleobaea), and the Soldier Butterfly (or "Tropic Queen"; Danaus eresimus). The adult stage (the butterfly) of these species will lay their eggs on the lower surface of milkweed leaves so that when they hatch the caterpillars can immediately begin to munch on the leaf tissue. As they eat, the caterpillars will also ingest the toxic, milky latex secreted from the wounded leaves. However, milkweed butterflies are “immune” to these toxins, and actually store them in their own body tissue to deter hungry birds from eating them (monarchs really are what they eat!). Check out this webpage about the role of milkweeds in the monarch lifecycle from mnarchwatch.org (http://www.monarchwatch.org/milkweed/index.htm). There is another species of caterpillar that is not part of the “milkweed butterfly” group known as the milkweed tiger moth (Euchaetes egle). There are also a bunch of butterflies, like the Eastern Black Swallowtail, that will feed on the nectar of milkweed flowers (unlike the caterpillar stage, adult butterflies do not eat leaves). However, the nectar of milkweed flowers does not contain the same toxic chemicals that the leaves contain, making the nectar safe for consumption by a wider variety of butterflies. This is a common challenge faced by plants – plants want to defend their leaves (food-producing organs carrying out photosynthesis), typically with chemical defenses or physical ones like thorns or hairs, while encouraging pollination of their flowers by insects. Milkweeds are a great example of this. Remember, just as there are many species of milkweed butterflies, there are also a number of different species of milkweeds (about 140 recognized species of Asclepias). Not all of them produce the same kinds or amounts of toxins characteristic of the Asclepias eaten by monarch caterpillars. Check out this great page from Duke University for pictures of different Aclepias (http://www.duke.edu/~jspippen/plants/asclepias.htm). Hope this helps! Enjoy exploring the wonderful world of plant-insect interactions!!! ~shireef
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