Thursday, January 2, 2014

Monarch Butterflies in the Winter Desert

Monarchs in Scottsdale in December
Every winter provides a mixed opportunity for monarch butterflies in the lower elevations of Arizona. After the first week of December, monarchs lose their urge to migrate and tend to settle locally for the season. When temperatures remain warm well into fall as they have this year, there is ample opportunity for monarchs to complete their growth cycle and flourish. Since they are tropical insects they do not usually survive a hard freeze unless they shelter in a warmer microclimate. But they are known to not only survive but thrive with a light freeze. This year so far, the weather is creating an ideal environment and monarchs are flourishing.

An early freeze and daytime temperatures only in the 50’s for four consecutive days were risky for
monarch winter survival. Non-native milkweed and nectar sources showed evidence of light frost damage. Yet, despite this short term assault, temperatures warmed and vegetation once again surged in growth. Reports of adult monarchs and larvae began rolling in from the greater Phoenix and Tucson areas. So far information shows a mixed population of breeders and some monarchs that appear to be in reproductive diapause. Our record high of 82 on December 17 could possibly trigger breeding in monarch populations spending the winter in the area – or not.

Monarch larva in Scottsdale
Overwintering strategies in the Southern United States of the monarch population are not well known but several studies are underway. Most to date have revealed that monarchs are breeding and laying eggs on non-native Tropical Milkweed, Asclepias curassavica, which has naturalized in Texas and Florida and is present in limited gardens in Arizona. Native milkweeds in these areas have already senesced and Asclepias curassavica is the only milkweed present. But Arizona offers a unique opportunity to monitor monarch breeding during the winter months since we have several evergreen milkweeds that are always in good condition and available. Desert Milkweed (Asclepias subulata), Pineleaf Milkweed (Asclepias linaria), Arizona or Narrowleaf Milkweed (Asclepias angustifolia) and Asclepias albicans are growing in areas where monarchs have been spotted. They offer an opportunity to monitor breeding and egg-laying. In some garden areas, Tropical Milkweed, Asclepias curassavica, is also planted alone or away from our native milkweeds. This provides a unique opportunity to monitor the presence and absence of monarch larvae.

If you see adult monarchs flying or monarch mating, egg-laying, larvae or pupae, please let us know at the Southwest Monarch Study via email or on our Facebook page. Your sightings and observations help us all learn more about the monarch butterfly migration and breeding in Arizona and the Southwestern United States.

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