Thursday, January 12, 2012

Breeding Monarch Butterflies in Phoenix - in January?

Female monarch feeding on tithonia
Seeing monarch butterflies around town? Monarch butterflies are out and about all over the greater Phoenix area with the warmer weather this winter. This week monarchs were spotted flying in Anthem while others were found in Ahwatukee. People are delighted and excited to find these graceful creatures fluttering and feeding in their yards.While parts of the Valley experienced a light dusting of  frost a few weeks ago, there are still plenty of flowers available for nectar, too.

Laying eggs on Arizona Milkweed, Asclepias angustifolia
 More unusual is finding monarch caterpillars in January - or monarchs laying eggs. Monarch butterflies are tropical by nature and undergo their long migration in the fall to spend the winter in Mexico or the coast of California. Their migration is influenced by the angle of the sun and other factors. But  monarchs that eclose in late November or December lose this celestial affect, so they often spend the winter in mild climates like we have in Phoenix. Monarchs in winter are usually in state of reproductive diapause  - they are not mating or laying eggs as a survival mechanism this time of year until Spring. How diapause works is not completely understood in monarchs.  Some scientists feel it is controlled by temperatures, others by the presence of milkweed (monarch host plant) or length of day.  Since September I've enjoyed monarch butterflies in my yard but haven't noted any egg-laying since the early days of November. This week that changed - I spotted this female (eclosed December 30th, tagged #60400) laying eggs on every milkweed she could find in my yard.

Dr. Chip Taylor, Director of Monarch Watch, explains: "Migratory monarchs are in what is known as reproductive diapause. This simply means that the butterflies have suspended reproduction. This condition is very labile, that is to say, easily broken. The non-reproductive condition is probably maintained by a balance of hormones (specifically one called "juvenile hormone" that triggers reproduction) and enzymes that break down this hormone. The diapause system breaks down, i.e.reproduction starts, when the butterflies are exposed to winter temperatures in the high 70s and low 80s over a few days. Warm nights and days accelerate the process. Monarchs can go from being non-reproductive to being ready to lay eggs in 4-5 days. Some of my colleagues believe that the presence of milkweeds in the winter is sufficient to trigger reproduction. Perhaps, but it is difficult to design experiments that separate a response to plants from that of temperature alone. Our experiments suggest that low temperature is both the main initiator and maintainer of diapause in monarchs. Once in diapause, monarchs exhibit a number of behaviors that seem to be designed to keep their body temperature and metabolism from becoming elevated. Once butterflies in transit become reproductive, the behavior shifts from migratory to local, mating occurs and females begin looking for milkweed plants."
Monarch egg on Desert Milkweed, Asclepias subulata.
Remember our warm temps reaching the low 80's the first days of January? They could easily have triggered some monarchs to break diapause, mate and lay eggs around town. So, check your milkweed and look and enjoy the breeding monarchs that visit your yard. As long as we avoid a hard freeze we may delight in finding new monarch caterpillars soon!


  1. Very informative post! Isn't nature fabulous?

    I envy you the Phoenix temperatures now, but not in the summer. It is regularly in the 50's here at 4592 ft, and not a butterfly in sight.

    1. Ah, but in the summer we come out your way! Canelo is my favorite spot in September when the monarchs really flood the area. We are having a very unusual winter. Much warmer than usual, but that can change with a snap of your fingers to a hard freeze. Delightful now, though! And, YES, nature is grand!