Wednesday, October 6, 2010

Phoenix Area Monarch Migration

A year ago monarch butterflies were everywhere. Here we are in the middle of the peak time of the annual Fall monarch migration in the Phoenix area - where are they? Queen butterflies (see photo on right) are abundant, but what about their annual family reunion with the monarchs as they pass through Arizona on their way to the coast of California or Mexico?

The first sighting of monarch butterflies was earlier than last year, but the number of monarchs has been lower. The scorching heat of September has likely put a lid on monarch activity around town as well as reproduction. September was the second hottest on record for the Phoenix area and monarchs don't like the heat. Instead of seeing monarchs flourish on milkweed patches, we are finding them hidden, nestled in willow or cottonwood trees near water where temperatures are cooler. We were hopeful that once the heat finally eased on Monday more monarchs would roll in. Perhaps they would have - if two days of severe thunderstorms hadn't dominated the weather! Lashing winds, pounding rain and marble to baseball size hail whipped monarchs wherever they are. Today is the last day of rain in the forecast and now cooler temperatures will dominate our weather. Last year monarchs were visiting milkweed patches around the Phoenix area by October 1st. Keep an eye out now that our weather finally is more favorable.

The monarch news isn't all bleak. Last Friday and again on Sunday a female monarch visited my yard early in the morning. Tatsuyo on South Mountain also saw one in her milkweed patch. Likely others are seeing similar activity. Ten days earlier Laura in South Scottsdale saw a female monarch laying eggs on Desert Milkweed, Asclepias subulata, in her yard. But the record breaking temperatures of 108 prevented any larva.


Bob and I were thrilled to see the monarch on Sunday morning laying eggs on the Desert Milkweed in our yard. (You can see her abdomen depositing eggs on the flower.) Last year we noticed that monarchs frequently lay eggs on the flowers or very fresh new growth of Desert Milkweed, Asclepias subulata. The tiny caterpillars easily eat the soft, fresh growth. As they get larger, the caterpillars can ingest the thicker branches. Both Tatsuyo and I are watching the eggs, hoping for caterpillars. I have three tiny ones from last Friday's egg laying activity that we hope will successfully grow. Stay tuned!

A question that often pops up is how can we tell the difference between a migrating monarch and a reproducing one? Right now in Arizona we likely have both. Migrating monarchs like each other! They are usually found in clusters and males and females are seen together without mating. Their reproductive urges are on hold - they are similar to a pre-adolescent. Sometimes it is easy to spot a female reproducing monarch by their egg-laying activity. Females usually lay eggs in the morning hours and you can spot them by their scooping-like activity around milkweed plants as they search for just the right place to lay their eggs. Reproducing males frequently set up patrols, gliding over milkweed patches over and over again, hoping a female flies into the area. Another difference between reproducing and migrating monarchs is the size of their abdomen. Migrating monarchs can weigh up to double the amount of reproducing monarchs. They nectar heavily to fuel their long migration. In the field you can often spot the thicker abdomen size. Their heavier weight often makes migrating monarchs slower, so they are easier to net and tag.

Want monarch butterflies to visit your yard? Local plant sales begin this weekend! Boyce Thompson Arboretum in Superior and the Desert Botanical Garden both offer various milkweeds, members of the Asclepias family.

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