I recently interviewed ecologist and butterfly expert Arthur Shapiro about the recent decline in some butterfly populations. He is a professor at the University of California, Davis; his expertise is California butterflies, especially the ones in northern California that he has studied for the last 37 years.
We discussed the findings of his study (listen to the EarthSky radio podcast here: “Why are some butterfly populations shrinking“) and at the end he mentioned something surprising. Urban and suburban butterflies, especially on the West Coast, are “now essentially dependent on introduced weedy plants,” he said. They need and love invasive, alien weeds!
This fact potentially pits two species of environmentalist against each other: The folks who campaign against invasive species and the people who want to protect, preserve and pump up butterfly populations. Shapiro described the clash like this: “If we remove the host plants that they are using, we will not have an urban or suburban butterfly fauna. So there is a trade off between tolerating exotic plants in the environment and maintaining your butterfly fauna, or being very hard-nosed about suppressing exotic plants and losing your butterfly fauna.”
Folks who like plants and gardens are not always taken with his advice about how to help butterflies.
“Yeah, I tell that to garden clubs and to master gardeners and so forth, and I tell them that the most butterfly friendly resources the average gardener can plant are zinnias and marigolds, which are not exactly endangered natives. And I’m looked at like I just told them they had two heads. But that is in fact the case. The best favor we can do butterflies dispersing through the urban environment looking for resources, is to provide them with resources useful to them. And while there are native plants that are useful, most of the best resources we can provide to butterflies – both nectar sources and larval host plants – are not natives in most parts of the country.
In California, for example, the common cheese weed is the most popular host plant for urban California butterflies. “We have four or five species that use it consistently,” said Shapiro.
So, all you gardeners out there: Would you leave some weeds in your garden if they would attract butterflies and help those flying beauties prosper? Is this one instance where you compromise on invasive species? I have a garden and we do get some butterflies. We also live near some woods, so maybe that helps. Lack of butterflies is not an issue for my garden, but it it was I think I would compromise a bit and leave something in there that would be good for butterflies. How about you? Post your comments here!
p.s. — Arthur Shapiro has a great butterfly site here, butterfly.ucdavis.edu, and here’s an article in National Wildlife magazine about butterfly population decline.
(Photo by Mike Baird bairdphotos.com)
It would be helpful if the actual species, of plants and of butterflies, were mentioned. Leaving it generic is not really making the point. I in fact do allow a particular weed, Hairy Bittercress, Cardamine hirsuta, to be in flower, because I saw Orangetip Falcates using the flowers. However, this year, with lots of Bittercress in bloom, almost no Orangetips.
Most of our garden flowers are not native, and if we did not have them, we would have less, if anything, of a garden and no butterflies either. The list of invasives is large, so which ones should one leave for butterflies? Mimosa? I’ve seen them almost covered with a dozen species in years past. But butterflies are declining here horribly, even while invasives are thriving: lots of large Mimosa in full bloom now, with not a single butterfly.
If the problem is no plants useful to butterflies except wild invasives, is the problem not enough wild invasives?
I looked back at the transcript of my interview with Arthur Shapiro, and what he said was that in many locations in the United States, and especially the West Coast, his team has documented that “the urban and suburban butterfly fauna is now essentially dependent on introduced weedy plants.”
He said zinnias and marigolds are the most butterfly friendly plants that gardeners can put in. He also mentioned that the common cheese weed in the mallow family is the most popular plant for the urban California butterfly fauna. Four or five species use it consistently.
Hope that helps.
-dan
Your correspondent must be back East if he has Falcate Orange-Tips (a “good bug,” too). It’s best to check with the Lepidopterists in your own local area. I come from Pennsylvania but I’ve been living in California for 37 years! There are no panaceas, and butterfly “droughts” can reflect purely local situations or much larger-scale processes. Tell your correspondent to contact the North American Butterfly Association (www.naba.org) for contacts in his own area.