Tuesday, October 4, 2011

Monarch Migration in Phoenix

I didn't know that she came but found the fruits of her labor. It was exciting to see the first male monarch butterfly visit my garden in early September (9/14) and surprising to see a female monarch laying eggs on Arizona Milkweed, Asclepias angustifolia, two days later. Hours later before dinner, my son Brian and I went out to see how many eggs we could find. I didn't see her lay many that morning.

Instead of just eggs, we started finding small second instar monarch caterpillars in the milkweed flowers! Not just a few - they were everywhere. While a female monarch can lay 500 eggs in her life time, predators will affect many and less than 10% will become a new butterfly. Earlier we already planned to bring some of the eggs and caterpillars to a protected environment to give them a better chance for survival. We knew we likely would not find them all. Luckily I already had many kinds of milkweed in one gallon containers as well as others planted in the garden so I could easily move the eggs, caterpillars and milkweed to a mesh hamper to protect them.

I never, ever expected to find so many monarch larvae around my yard! Usually ten to twenty monarch caterpillars are good numbers in our desert gardens. Instead I kept finding more and more larvae wherever I looked in different milkweed patches. Yesterday I tried to get a better grasp on the numbers. There are 50 pupae on this "tree", seven new pupae in the hamper, seven larvae were now making silk pads and there were at least 21 5th instar larvae still on outside milkweed plants.

Yesterday the first six eclosed. Five were females and one male. So a couple of  female monarchs left over 80 eggs in my yard! By using degree days, we figured the first female likely came through the yard on Sunday, September 11, while I was out of town. The second female arrived September 16th. In previous years we didn't see egg-laying until the beginning of October during the time of the peak monarch migration through the Phoenix area.  
So keep your eyes open during this premier time of the monarch migration through the greater Phoenix area! For a time we will likely see breeding and migrating monarchs around town. With the cooler weather heading our way and the winds shifting to a more favorable direction, look for monarchs in the air. Don't forget to look in unusual places, too, for any eggs, larvae or pupae they may leave behind during their short time with us.

You can read more about the status of the monarch migration and population this year on the Monarch Watch Blog by Dr. Chip Taylor. How can you help? Grow milkweed! Start your planting list for the Fall plant sales today.


  1. Very exciting! I don't have Monarchs but I found 5 Queen caterpillars on My subulata this weekend. I live in far NE Scottsdale. I

  2. Where there are queens, the monarchs will follow! Keep looking - I had two female monarchs laying eggs in my yard today. Two days ago there was a mating pair. With our warm weather we may see monarchs hanging around longer than usual. Enjoy this special migration season!