If you like to garden, then you probably know what milkweed is, but did you know there are two kinds of milkweed found here? One is native and one is not. And you may have seen butterflies attracted to them both.
Many butterfly enthusiasts in Florida recommend swapping “tropical” milkweed for “native” milkweed to stop the spread of a parasite that can kill the monarchs. But new research shows that the plan won’t work.
At the Panhandle Butterfly House in Milton, dozens of actual butterflies are displayed in presentation boxes. But a few steps across the yard is a live butterfly warm house. Getting inside requires passing through a special intake door that forces air inside in order to keep the butterflies from escaping.
A naturally occurring parasite threatens these monarch butterflies. It’s a parasite called OE (Ophryocystis elektroscirrha), and it thrives on a plant that, ironically, is mandatory for monarchs’ survival. The plant is milkweed. Pam Murfey, the Panhandle Butterfly House’s Executive Director, knows a lot about the milkweed plant and the microscopic OE spores that live on some of the monarchs in here.
“The OE spores and other viruses can get into those plants and then it gets transferred to one monarch, then the caterpillars, and it keeps spreading because you know, they go from plant to plant.”
Andy Davis, an ecologist at the University of Georgia, has been researching the OE parasite and its proliferation in Florida for years.
“The way it transmits is that an infected monarch, as the females are depositing eggs on milkweed, those little football-shaped spores fall off of her abdomen and onto the milkweed leaf that she's laying the eggs on," Davis explained.
Caterpillars then eat the leaf, and the spores, ingesting the parasite. This causes the cycle to start all over. The result can be an agonizing death for the monarchs.
READ MORE: Monarch butterflies' white spots may help them fly farther, scientists say
"When monarchs are really, really heavily infected most of the time they just die trying to get out of their pupa case," Davis said. "Sometimes they turn into a ball of mush, sometimes they can get out, but then their abdomens are really nasty looking because of all the damage from the spores and the infection. Their wings are all crinkly and they're just sort of crawling around in the bushes, dying a slow death because they can't fly.”
The issue with milkweed
The rampant spread of the OE parasite is caused by many people believing that adding tropical and native milkweeds to their backyard gardens was beneficial for monarchs. That’s because most butterflies have a single plant as a food source for their caterpillars. For monarchs, that plant is milkweed. Without it, the larva will not develop into butterflies. More milkweed plants equal more food for monarch caterpillars. More milkweed plants also equal faster spread of the parasite.
For years many experts said that the tropical milkweed plant, specifically, was the main source of transmission because it does not die back in the winter.
“The issue with tropical milkweed is that because that species lives so much longer, it's the potential for that parasite to build up to higher levels on that plan,” says Beth Bolles with the Escambia County Extension Service.
Bolles advises to get rid of all tropical milkweed from your garden. What should you grow instead?
“You grow natives," she said. "We do have two versions of a swamp milkweed. So there are options out there if people can just be diligent in not growing the tropical and growing those natives.”
But Ecologist Andy Davis says his research shows that, in Florida, the switch to native milkweed is not the solution.
“People think that as long as you're buying native milkweed in Florida, you're solving this OE problem," he said. "It's an assumption or an extrapolation of some evidence from other places in the country, anywhere else in the country, native milkweed is the answer. Native milkweed will die back in the winter. All of the OE spores that were on those plants then disappear, and then the plant comes back in the spring, fresh from the ground (with) new leaves. In Florida, almost every monarch that's flying around is infected. And every monarch that lands on any milkweed in Florida, any milkweed, is going to drop its OE payload on that milkweed.”
Back inside the Panhandle Butterfly House, Pam Murfey points out her milkweed plants — which do look like a weed, but with a cluster of pink blooms on some of the stems.
“Our front garden is all native plants," she explained. "We have the swamp milkweed. That's native."
She says she is keeping her native and non-native tropical milkweed — right next to the fluttering monarchs.
“We've been using it for many years in the butterfly house because when we're rearing our monarch caterpillars, we have to have that ready food source," said Murfey. "And so it's one of the fastest growing. So you're able to feed those caterpillars and help them grow. It's kind of a choice, I think, that people need to make as far as what they're going to use if it's going to be native or non-native. The main thing is we encourage people to trim in the fall. Cut it back, don't let it produce.”
A new recommendation
But Davis says cutting back the plant won't work.
“As soon as the next leaf sheds, the next monarch that flies in your yard will drop its spores on that plant, and therefore your plant will then become an infectious, contaminated spot again," he said. "Just plant native milkweed and that will fix the problem. But it doesn't. In Florida, there are just already too many highly-infected monarchs flying around. It doesn't really matter if you have native milkweed or nonnative milkweed, because those infected butterflies flying around are going to use your milkweed, no matter what it is, to make more infected butterflies. The only way to deal with this is to not have milkweed — period.”
Dr. Davis says that there is no shortage of monarchs in Florida, and they have plenty of milkweed to use, so there’s no need to have it on your property. His research shows that 50% of monarchs in Northwest Florida are infected.
“All milkweed in Florida, I don’t care what type of species it is, it is now covered in OE spores. My personal recommendation to people in Florida is to just get rid of your milkweed. That's a hard thing for people to digest. Removing your own backyard milkweed is not going to solve all of Florida's problems, but it is going to solve the problem in your backyard.”
Copyright 2024 WUWF
