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#7 - Tropical Milkweed (an ecological trap)

Most members of the order Lepidoptera (butterflies and moths) are host specific, which means they are dependent on one very specific type of plant to finish their reproductive cycle. The reason for this is that herbivorous (plant eating) insects have to evolutionarily develop an immunity against certain toxins that plants use to protect themselves. In other words, these insects have undergone a coevolution with their host plants and can, in most cases, not consume exotic (or non-native) plants, even when closely related.

One exception is the iconic monarch butterfly whose larvae are specialized on plants in the large family Apocynaceae, also called milkweeds because of their milky sap that is toxic to most other insects and mammals. The monarch butterfly (and also the queen) not only uses native but also exotic milkweeds like the ubiquitous tropical milkweed (Asclepias curassavica) that is commercially available in almost every hardware store in Florida because of its undemanding character and its fast growth rate. These traits are also the reason why this plant is listed as an invasive species (see photo of tropical milkweed on the ELC campus.)

But invasiveness is not the only problem with tropical milkweed, it can also function as an ecological trap. Unlike tropical milkweed, all Florida native milkweeds are winter dormant and grow back in the spring. This triggers the migration habit of the butterfly which would otherwise possibly freeze to death in Central Florida’s winters. Winter dormancy of native milkweeds is also important to reduce or avoid the transmission of the protozoan parasite OE (Ophryocystis elektroscirrha) which is another reason for the rapid decline of these butterflies.

Cutting the plant down in the winter is often recommended. But do you know how many seeds your plants disperse into our natural plant communities? Give invasive species an inch and they take a mile!

If you want to learn more about Florida, visit the Environmental Learning Center in Vero Beach!


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