Each year, the species makes the several thousand mile trip from Mexico to Canada. A single butterfly has been known to travel as far as 265 miles in a single day.
My colleague Ken Herman asked me whether the border wall proposed by Republican presidential candidate Donald Trump would stymie butterfly migration.
The answer, apparently, is no.
Austin entomologist Mike Quinn tells me the butterflies spend their winters in forested mountains in Mexico about 10,000 feet in altitude. Specimens have even been collected by airplane.
Glider pilots have reported spotting monarchs at altitudes as high as eleven thousand feet, according to the organization Journey North, which provides information about the monarchs.
More from Journey North:
The height monarchs fly depends on which way the wind is blowing. When winds are from the south, monarchs fly very low. Or, if the winds are strong enough, they don’t fly at all. They wait patiently in low areas with lots of trees (if available) for the winds to turn around. During these times, they mysteriously accumulate. This is when they form their gigantic roosts and people are dazzled by large curtains of hanging butterflies at night and early morning.
When the winds turn around the story is very different. During a typical morning with correct winds, monarchs will burst out of their roosts after they have warmed themselves enough to fly. Remember they are cold blooded creatures (poikilotherms in scientific lingo) and must depend on sunlight (radiation) to warm their flight muscles. Once they leave the roost they may fly to a point in full sun where they bask some more or they may search for a morning thermal, and ride the rising air upward, twisting and turning like a feather caught in the wind.
In any case, Donald Trump’s border wall could be as high as 55 feet tall. The monarchs clear buildings and other obstacles that high along their flyway.
The border wall does present other problems of an environmental bent: Already the border wall has bisected nature preserves and presented challenges for endangered species accustomed to roaming parts of northern Mexico and South Texas, such as ocelots.