The steep de­cline of monarch but­ter­flies

A 37-year study finds that the pop­u­la­tion of the or­ange in­sects vis­it­ing Florida has fallen sharply.

Tampa Bay Times - - Front Page - BY CRAIG PITTMAN Times Staff Writer

A nearly four-decade study finds an 80 per­cent de­cline in the or­ange in­sects in Florida since 2005. A sci­en­tist calls the study’s re­sults “alarm­ing.”

Ev­ery year thou­sands of monarch but­ter­flies dance through the air over North Florida, trav­el­ing be­tween their win­ter refuge in Mex­ico and their reg­u­lar homes along the U.S. Atlantic coast­line. The col­or­ful pageant at­tracts flocks of tourists who are ea­ger to bear wit­ness to this sprightly migration.

Ev­ery year, though, there have been fewer and fewer of the princely in­sects to see.

A new Univer­sity of Florida study — at nearly four decades, the long­est of its kind — has found that the num­ber of cater­pil­lars and but­ter­flies in North Florida has been de­clin­ing since 1985.

Since 2005, the num­bers have dropped by 80 per­cent.

“It’s alarm­ing,” said as­so­ciate pro­fes­sor Jaret Daniels, a coau­thor of the study.

He pointed out that if a beloved and widely known species such as the monarch can be pushed so eas­ily to­ward ex­tinc­tion, imag­ine how much more im­per­iled are other, less well­known ones.

“It ex­em­pli­fies all the is­sues we’re hav­ing to deal with in con­ser­va­tion,” he said.

The sci­en­tists in­volved in the study say the causes of the de­cline are not en­tirely clear, but they be­lieve there are two ma­jor fac­tors at work.

One is the de­struc­tion — by de­vel­op­ment or agri­cul­ture — of ar­eas that had been planted with na­tive milk­weed, the fa­vorite food of young mon­archs. The other is the wide­spread use of a her­bi­cide called glyphosate, of­ten ap­plied to farm­ers’ fields to kill weeds. One of the weeds it kills is milk­weed.

The study was launched 37 years ago by an in­ter­na­tion­ally known monarch ex­pert named Lin­coln Brower. He died this summer at age 86, just be­fore the study was pub­lished in the Jour­nal of Nat­u­ral His­tory.

Brower be­gan study­ing mon­archs in the 1950s. He was in­stru­men­tal in lo­cat­ing the fir trees in Mex­ico where they spend the win­ter be­fore head­ing back for Florida. In their win­ter home, about 80 to 100 miles west of Mex­ico City, the trees are thick with the or­ange in­sects, and when they flap their wings the sound is like thou­sands of leaves rustling.

“It has the most com­pli­cated migration of any in­sect known,” Brower told the Chicago Tri­bune in 1998. “Some­how they know how to get to the same trees ev­ery year. It’s a highly spe­cific be­hav­ior that is unique to the monarch but­ter­fly.”

Dur­ing their re­turn trip north, a new gen­er­a­tion of mon­archs is born en route. They grow from lar­vae to cater­pil­lars, then turn into but­ter­flies to con­tinue the rest of their flight.

That’s why check­ing on their pop­u­la­tion ev­ery time they landed in North Florida al­lowed sci­en­tists to de­ter­mine what was go­ing on with their pop­u­la­tion num­bers.

“Florida is kind of a stag­ing ground for the re­col­o­niza­tion of much of the East Coast,” Daniels said. “If these pop­u­la­tions are low, then the north­ern pop­u­la­tions are go­ing to be at a sim­i­lar abun­dance level.”

The most fa­mous spot in Florida to watch mon­archs is St. Marks Na­tional Wild-

life Refuge, which spon­sors an an­nual Monarch But­ter­fly Fes­ti­val ev­ery fall. That catches the but­ter­flies on their way south.

Un­der Brower’s di­rec­tion, a team of sci­en­tists closely mon­i­tored how many mon­archs showed up each spring head­ing north.

Their se­lected site was a sin­gle her­bi­cide-free cat­tle pas­ture in Cross Creek, one­time home of ac­claimed Florida author Mar­jorie Kin­nan Rawl­ings, who wrote The Year­ling.

“Lin­coln made the con­nec­tion with that fam­ily 37 years ago and they’ve been in­cred­i­bly gra­cious to con­tinue to al­low us ac­cess,” Daniels said.

At the study site 20 miles south of Gainesville, the team gath­ered ev­ery year to ex­am­ine the pas­ture’s milk­weed plants for any cater­pil­lars. They also cap­tured adult monarch but­ter­flies to check the growth or de­cline of the pop­u­la­tion.

The 37 years they spent do­ing this is roughly the equiv­a­lent of 140 gen­er­a­tions of mon­archs.

One find­ing of the study: Mon­archs time their de­par­ture from Mex­ico in the spring so it co­in­cides with the op­ti­mal growth of milk­weed in Florida and other South­ern states.

While adult mon­archs can eat a variety of plants, the young ones’ diet con­sists of noth­ing but milk­weed. The plants con­tain tox­ins that they store up to ward off preda­tors.

Florida is home to 21 na­tive species of milk­weed. Three types are best for the mon­archs, Daniels said: swamp milk­weed, pinewoods milk­weed and, of course, but­ter­fly milk­weed.

Al­though Brower has died and the study has been pub­lished in a sci­en­tific jour­nal, the work will go on, Daniels said.

The hope is that the monarch migration will con­tinue too.

Pho­tos cour­tesy of Florida Mu­seum of Nat­u­ral His­tory

Monarch but­ter­flies on their migration north cre­ate an­other gen­er­a­tion to fin­ish the trip.


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