In mid-september, after many weeks of 100+ degree temperatures, the summer temperatures finally broke. A storm front brought cooler temperatures and the first bit of rain that we had seen in weeks. We lived at the base of mountain range on the south side of Monterrey, Mexico, just a five minute walk from hills covered in semitropical shrubs and stunted trees.
One afternoon, I walked out my front door and noticed thousands of bright yellow sulfur butterflies gliding over our little home. They were all flying south and as many as 20 or 30 would pass just overhead within a matter of a 10 seconds.
I decided to go for a walk up to the adjacent hill and I found dozens of other species of butterflies visiting a dozen or more blooming shrub species. Each species of plant tended to have specific butteflies visiting its flowers, although they were a few generalist butterflies that appeared to be visiting several different species of plants.
I wondered if moth activity would also spike during the night. I took walk the next morning to the hill and found the eaves of a small school covered with no less than two dozen species of moths. They had all emerged within the last 24 hours and I assumed they must have been responding to the same shift in weather that had triggered the butterfly activity.
The activity of the butterflies and moths waned over the next few days. After a week, I would guess that less than half of the butterfly and moth diversity had dissappeared. I have struggled to find more information on these fall emergence patterns of butterflies.
Empty Forests 