Du­bi­ous dis­trac­tion

Monarch but­ter­fly ad­vo­cates at odds over whether milk­weed plots in US help or hin­der the cause

Northwest Arkansas Democrat-Gazette - - STYLE - ADRIAN HIG­GINS

The brutish com­mon milk­weed, not a choice gar­den plant, is set­ting its strange pods now that its muddy pink blooms are wan­ing, but other milk­weeds are still flow­er­ing, and in a pret­tier way.

The vivid orange clus­ters of but­ter­fly weed are lin­ger­ing in the heat, and the swamp milk­weed is erupt­ing with its creamy white blooms. Both are na­tive peren­ni­als that de­serve a place in a sunny gar­den, the for­mer for dry sites and the lat­ter for tricky, moist to wet ar­eas.

The milk­weed is linked in na­ture and in our imag­i­na­tion to one iconic in­sect, the orange and black-veined monarch but­ter­fly. The cater­pil­lar takes up the poi­sons in the milk­weed, ren­der­ing the monarch un­palat­able to most preda­tors. As mirac­u­lous as this is, the monarch can seem in­fu­ri­at­ingly ab­sent now for the gar­dener who wants to nur­ture this pol­li­na­tor.

This has to do with the monarch’s no­madic na­ture. As ev­ery school­child knows, each win­ter the mon­archs clus­ter by the mil­lions in the moun­tain­ous oy­amel fir forests of cen­tral Mex­ico and then head north for sum­mer breed­ing grounds in north­ern states and Canada. On their spring mi­gra­tion, they use the milk­weeds not just for nec­tar but as a food plant on which to lay eggs. Many make the per­ilous jour­ney to adult­hood, grow wings, and then also head north­ward.

By late sum­mer, these mag­nif­i­cent but­ter­flies no­tice the shorter days and be­gin their epic mi­gra­tion back to­ward Mex­ico. In the mid-At­lantic re­gion some linger, sup nec­tar and may lay more eggs in the hope of get­ting an­other gen­er­a­tion on the wing in time for win­ter south of the bor­der.

I love to watch them in the gar­den in the clear blue light of Septem­ber, when they seem to rise and fall with a sin­gle flick

of the wings and with none of the mad frenzy of smaller but­ter­flies.

In spite of its fa­mil­iar­ity, the monarch has be­come a poster in­sect for the de­cline and threats fac­ing all pol­li­na­tors in an age of cli­mate change, pes­ti­cide- driven agri­cul­ture and habi­tat loss. The phe­nom­e­non of their win­ter as­sem­bly makes track­ing their num­bers rel­a­tively easy, and the num­bers have crashed. Once, hun­dreds of mil­lions would over­win­ter in such abun­dance that the tree boughs would bend. By 2014, the pop­u­la­tion had dropped to an es­ti­mated 34 mil­lion. In the past two years, the num­bers have re­bounded — last win­ter it was up to 145 mil­lion — but the over­all tra­jec­tory is one of un­mis­tak­able de­cline.

As part of the ral­ly­ing for the monarch, gar­den­ers have been en­cour­aged to plant milk­weed to pro­vide a host­plant cor­ri­dor across the in­sect’s vast range.

An ecol­o­gist at Cor­nell Uni­ver­sity, Anurag Agrawal, doubts the prac­ti­cal value of this hor­ti­cul­tural trend. He is the au­thor of the newly pub­lished Mon­archs and Milk­weed. Agrawal says that although milk­weed habi­tat has been lost, there is still plenty of wild com­mon milk­weed out there, es­pe­cially in the east­ern United States. Plant­ing milk­weed in your gar­den “is a re­ally feel-good thing, but it’s not re­ally the con­ser­va­tion so­lu­tion,” he said.

But that shouldn’t stop gar­den­ers from plant­ing it, he says. “You get to watch this in­cred­i­ble bi­ol­ogy un­fold. Maybe the sin­gle most im­por­tant thing we can do for con­ser­va­tion in gen­eral is to give peo­ple an ap­pre­ci­a­tion of na­ture.”

Jef­frey Glass­berg, pres­i­dent of the North Amer­i­can But­ter­fly As­so­ci­a­tion, agrees. “All the stuff that the prob­lem with mon­archs is there aren’t enough milk­weeds is pretty du­bi­ous,” he said, adding that gar­den­ers should still plant it.

What’s at the root of the monarch’s de­cline? Glass­berg is in­clined to think it’s the degra­da­tion and loss of the over­win­ter­ing ter­ri­tory in Mex­ico and the wide­spread con­tem­po­rary use of a class of pes­ti­cides called neon­i­coti­noids, an is­sue linked to prob­lems with hon­ey­bees and other bee species.

The other de­bate with mon­archs and milk­weeds comes down to a ten­der milk­weed species from Mex­ico known as trop­i­cal milk­weed. This is a stun­ning plant, with bushy blue-green fo­liage and clus­ters of red and yel­low flow­ers that just keep com­ing un­til the first frosts. “My take is the trop­i­cal milk­weed is spec­tac­u­larly beau­ti­ful, very easy to grow, and mon­archs love it,” Agrawal said.

So what’s the prob­lem? Some ecol­o­gists say that the ex­ten­sive gar­den plant­ings in balmy Gulf States are caus­ing mon­archs to get side­tracked on their south­ward mi­gra­tion and that this is con­tribut­ing to the spread of a pathogen that is killing or weak­en­ing the monarch.

My hor­ti­cul­tur­ist friend Janet Draper says this dou­ble whammy may not be con­fined to the south­ern edge of the United States. In Oc­to­ber, I was in her Wash­ing­ton gar­den ablaze with trop­i­cal milk­weed (and much more) and well stocked with mon­archs that were in the process of tak­ing nec­tar and lay­ing eggs on the milk­weed. She showed me cater­pil­lars and chrysalides. If they ever stood a chance of over­win­ter­ing here, they were doomed by the sub­se­quent ap­pear­ance of the dis­ease par­a­site Ophry­ocys­tis elek­troscir­rha. Mor­ti­fied that she had been the agent of this, she re­solved not to grow trop­i­cal milk­weed this year.

Agrawal says there may be a prob­lem in the Gulf States with trop­i­cal milk­weed as a con­trib­u­tor to the dis­ease. “The de­fin­i­tive long- term study hasn’t been done,” he said. “The ev­i­dence at hand sug­gests some cau­tion.”

But Glass­berg says there is lit­tle ev­i­dence that trop­i­cal milk­weed will weaken pop­u­la­tions and no ev­i­dence that mi­grat­ing mon­archs are be­ing trapped. He said the par­a­site is com­monly found in monarch pop­u­la­tions in Cal­i­for­nia and Hawaii, away from trop­i­cal milk­weed.

At the North Amer­i­can But­ter­fly As­so­ci­a­tion’s Na­tional But­ter­fly Cen­ter in Mis­sion, Texas, he said, “tens of thou­sands of mon­archs mi­grate through our prop­erty, which is loaded with trop­i­cal milk­weed.”

Glass­berg can con­ceive of a day when the re­main­ing fir forests and over­win­ter­ing grounds in cen­tral Mex­ico — now down to a few acres — are wrecked by cli­mate change and this once-great nat­u­ral spec­ta­cle will van­ish. In that event, the mon­archs will prob­a­bly over­win­ter on the Gulf Coast, and trop­i­cal milk­weed “may turn out to be the thing that saves the monarch,” he said.

If you want to grow it in the Mid-At­lantic re­gion and are wor­ried about it harm­ing the monarch, you can rip it out in late Au­gust. Draper points out that this is when it’s just about hit­ting its stride.

Agrawal, who lives in Ithaca, N.Y., is un­per­turbed by the sight of cater­pil­lars that clearly won’t make it be­fore the frosts of fall.

“Up here, if they don’t start fly­ing south by Sept. 15, they won’t make it to Mex­ico,” he said. “But in Oc­to­ber, they’re here, cater­pil­lars, but­ter­flies. They’re the liv­ing dead, but that’s just how the bi­ol­ogy works.”

Spe­cial to the Demo­crat-Gazette/DAVID HOGE

A monarch but­ter­fly feeds on trop­i­cal milk­weed. Some ecol­o­gists are sug­gest­ing that trop­i­cal milk­weed may be con­tribut­ing to the de­cline of the mon­archs be­cause ex­ten­sive gar­den plant­ings in balmy Gulf States are caus­ing mon­archs to get side­tracked on their south­ward mi­gra­tion and that this is con­tribut­ing to the spread of a pathogen that is killing or weak­en­ing the monarch.

Demo­crat-Gazette file photo

Trop­i­cal milk­weed blooms longer than na­tive vari­a­tions of the plant.

Hand­out

While monarch but­ter­flies re­quire milk­weed to lay their eggs, they also stock up on nec­tar from other flow­er­ing plants.

Spe­cial to The Wash­ing­ton Post/ANURAG AGRAWAL

In his new book, Mon­archs and Milk­weed, Anurag Agrawal ex­plains how monarch cater­pil­lars can eat the tox­ins in milk­weed and be­come poi­sonous to most preda­tors with­out harm­ing them­selves.

The Wash­ing­ton Post/ADRIAN HIG­GINS

Gar­den­ers love trop­i­cal milk­weed for its beauty, but some ob­servers fear it could be harm­ing rather than help­ing the monarch.

Hand­out

A monarch cater­pil­lar munches on milk­weed.

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