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Wednesday - November 19, 2008

From: Austin, TX
Region: Southwest
Topic: Butterfly Gardens
Title: Texas native variety of butterfly weed
Answered by: Nan Hampton

QUESTION:

Which variety of Butterfly Weed is the native Texas variety? I want to know which one supplies the proper defense against birds to the Monarch butterfly through it's nectar? I have heard that the non-native one does not and I can't figure out which one this is. Is it the one with red and yellow flowers? Thank you!

ANSWER:

There are several species of butterfly weeds or milkweeds that are native to Texas. It isn't the nectar that the adults feed on, however, that supplies the main defense against birds. The main defense comes from the foliage of the milkweeds (Family Asclepiadaceae) that the larvae feed on. All milkweeds contain cardiac glycosides which are sequestered by the monarch larvae and then transferred to the adult stage at metamorphosis. These glycosides cause vomiting in 12 species of birds. After such an incident the bird learns that butterflies with the monarch's pattern are distasteful and, thus, learns to avoid them. Adults feed on nectar from various flowers, even milkweed flowers; however, they acquire another chemical defense, pyrrolizidine alkaloids, from the nectar of flowers in the Family Asteraceae (Aster Family). These alkaloids, however, are not as effective in defending against predation as the the glycosides obtained by the larvae from feeding on milkweed foliage.

You can see a list of Texas Milkweeds and the Caterpillars that Feed on Them compiled by Mike Quinn, President of the Austin Butterfly Forum. On this list you will note that Asclepias asperula (antelope-horns), Asclepias latifolia (broadleaf milkweed), Asclepias oenotheroides (zizotes milkweed) and Asclepias viridis (green antelopehorn) are the most important ones. All four species occur in Travis County, but the commonest one is A. asperula (antelope-horns). I think the one you are referring to as the one with red and yellow flowers is Asclepias tuberosa (butterfly milkweed). It is a beautiful plant and is certainly a foodplant for the larvae. It also supplies nectar for adults, but it is not very common in the area and is not considered one of the most important milkweeds for monarchs. Many of the other milkweeds on the list occur in Travis County as well. You can read more about these other milkweeds in our Native Plant Database by searching on their scientific name.