September 23, 2024

It’s September and monarch butterflies (Danaus plexippus) are moving through. In fact, September through early October is peak time for the long distance migrants to cut across our state. Sure, you’d see many more if you were in the mountains or along the coast due to the concentration factor. A combination of geographic features (physical barriers) and regional wind conditions tend to concentrate the insects on mountain ridges and coastal dunes when conditions are right.

Here on the Piedmont, the flight is more disbursed, spread out over a wide front. Even so, if you sat yourself down on a bench with a clear shot of the sky and faced in a general NE direction I bet you’d see at least a dozen or so monarchs winging by overhead throughout the day. (Try it during the last few days of September or first few of October on a day with light SW winds, and bring your binoculars). That’s not counting the monarchs you’d see sipping nectar at a flower garden durning this same period.

The monarchs we see going through now are members of the so-called fourth generation of monarchs. They are the descendants of and last in line from the butterflies that started northward by leaving their winter roosts in Mexico last March.

As the fall migrants travel along, generally in a southwesterly direction, they may pause to lay eggs on any milkweed they encounter along the way. The larvae that hatch will spend the next several weeks feeding and growing, pupating, then continuing on the journey. That is, if the weather cooperates and the leaves of the plants survive. It’s late in the season and many of these southbound monarchs will not make it to their ultimate journey’s goal, central Mexico. They will perish.

Our milkweed here at the museum is fading fast. Any caterpillars still on the plants are living on the edge. Do they have enough time to feed? Will the leaves remain on the plants long enough to be consumed? Will they have enough time to pupate and become adults? Only time will tell. It’s a long and treacherous trip ahead of them and time is short.

The larvae and adults you see in these photos were in the garden in front of the Butterfly House here at the Museum of Life and Science. It was the second week in September. I expect more monarchs will be flying by in the next few weeks but I doubt we’ll see any more eggs deposited. I don’t think there’ll be any leaves to lay them on.

Any more monarchs that show up in our garden will have no other option but to fuel-up and keep trekking southwest.