mariposas de las noches

Dispatch from the road...

If you’ve spent time in the neotropics in late fall, chances are you may have seen Urania fulgens, a swallowtailed, diurnal migratory moth (often mistaken for a butterfly), sometimes called the Green Page, or Colipato Verde. In the last few days here in Central America, I have seen thousands, nearly every single one sticking to a similar bearing. In the lowlands, over water, in the mountains, in the cities, in the sun, in the rain – a steady stream of resplendent black and green moths (Urania signifies the green of Uranus, and fulgens translates as "brilliant"). I rarely see them land, but this one was up under the canopy of a filling station.

These moths sometimes travel 60 to 100 miles a day in their periodic mass movements within their range, which spans from northern Mexico into northern South America, although I have seen them (or a similar species) moving through Havana in mid-winter. These impressive movements are triggered by the increasing toxicity of their larval food plants, in the genus Omphalea. It is one of the countless examples of an endless evolutionary arms race between plants their consumers that is so prevalent in the tropics.

To defend against the herbivory of the moth larvae, Omphalea plants contain poisonous alkaloids. In response, Urania larvae have adapted with an immunity to the toxins. As Omphaleas face increasing pressure from growing regional populations of Urania, the plants produce more alkaloids. When the toxicity finally reaches a level that equals success for the Omphaleas, rendering them inedible, the Urania moths move out of the area in search of less poisonous populations of Ompheleas. Apparently, this cycles repeats itself on various scales throughout the range of the moth.

A conspicuous example of evolution is on the move here in Central America.

UPDATE on the large movement of 2005, noticable even in the U.S.  Includes links to further primary literature clarifying the relationship between the toxicity of Omphaleas and the movements of Urania.  In short, Omphaleas produce increased toxins not over generations, but as individual/localized groups responding to grazing pressure by Urania larvae. See "Host plant toxicity and migration in the day flying moth Urania."

Comments

[tony g]

i'm just plain jealous . . .

wondering if you've thought more about an inordinate fondness . . . quite a bit of excellent writing on the web in the last week or so . . .

tg