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A time for going home!
Monarch Butterfly Field Notes from Mexico by Dr. Bill Calvert

March 12, 2009

This week, with the Iowa County Conservation Board Naturalists, we visited two very different butterfly colonies.

The first, considered to be one of the Chincua colonies, was high up in a canyon on the north side of the Sierra Chincua massif and accessed through the delightful colonial town of Senguio. The canyon is named Ojo Caliente; the approximately one half hectare, highly dispersed colony was near the Llano de Koala. We arrived late, but in time to see the monarchs reforming their clusters in late afternoon.

The other colony was the lower part of the Rosario colony now spread out for a least a kilometer in a canyon called Arroyo Grande. This colony was above the settlement of La Salud. We arrived early and a combination of slightly cooler than average temperatures and some early morning clouds kept the ambient cooler than usual and the butterflies less active than normal. But we were not to be disappointed. By noon tens of thousands were pouring down through the forests and above the canopy. Many were headed to nearby fields where water seeps were present. Many were nectaring on Eupatorium and Senecio at field edges. Others were watering along streamsides within the forests. A quick but limited count of those nectaring at field edges revealed that 100% were male. These males were likely stocking up on the sugars needed to power their mating activities.

Within the forest, like parachutes of colored cardboard, numerous monarch pairs floated down from the canopy, resulting in reluctant embraces on the forest floor. Reluctant because the females were clearly trying to avoid being clasped by the males. A paradox because the females clearly need the nitrogen from the male spermatophores to make egg yoke.

The male is seldom successful in his courtship – maybe only 10% of the time does he attach to the female and attempt to fly off to a perch in a tree or shrub. And 10% of the time he mistakenly grabs another male. Strangely, the male brought down – also clearly reluctant – pumps his labial palps open and close just as the female does when she is brought down by a male. At any one time, ten to twelve mating pairs could be observed struggling in the ground within a small area.

Early that morning when there was little butterfly activity within the forests other than basking behavior, high up over the forest canopy and fields, monarchs were seen flying northwards. We surmised that these were those that had begun the migration home just as we will do this coming Saturday!

For information on future Monarch adventures to Mexico, contact or


Dr. Calvert

Adriane Grimaldi

Monarchs in the sky.
Can you find the pair in nuptial flight? (See larger image.)