Today Soni (CBC horticulturist) came down to my office and said “You should see all the monarchs in the outdoor butterfly garden. They must be part of the fall migration. Why don’t we tag them?”’
Surely by now most people are aware of the amazing migration undertaken each year by the fall generation of monarch butterflies. As the temperatures cool and the days shorten, monarchs emerging from their chrysalids are cued to head south. Somehow they “know” that their survival depends on it. Before winter sets in, millions of individuals – basically the entire eastern population – start to fly southwest, towards the remote mountain sites in central Mexico where they will spend the winter hanging on the branches of fir and pine trees.
|Soni netting butterflies|
The spring and summer generations behave very differently. After emerging from its chrysalis, one of the first things a new butterfly typically does is look for a mate (“nature abhors a virgin” as my friend Phil DeVries would say). Mated females search for milkweed plants on which to deposit their eggs; males look for more females! These fair-weather generations probably live for a month or so as adults. The autumn generation, however, does not mate, but saves its energy for the long journey ahead. As fall approaches, butterflies stock up on nectar, packing on fat for the flight and for several months of hibernation.
At the northern edge of the population (southern Ontario/northern Great Lakes area), the migration starts in late August, with butterflies flying on average about 50 miles a day and picking up more migrants as they travel south. By early to mid October, monarchs are streaming through Texas. Virtually the entire eastern population passes through our state – but most of the migrating butterflies pass to the west of us, through Dallas and Austin and San Antonio, then over to Del Rio and into Mexico. Since fewer butterflies typically pass this way, the coastal migration route is not as well known. All the more reason for us to get out there and tag!
|How to tag a monarch|
Monarch researchers began tagging monarchs back in the early 70s, even before anyone knew where the migrating monarchs were ending up (the roost locations were discovered in 1975). Tagging data collected over the years has enabled us to map the distribution of the population, and to understand that a single generation makes the long trip south and then heads north again after spending the winter, largely dormant, in Mexico. This is hard for some people to understand, especially given that most butterflies only live for a few weeks. The migrating/hibernating monarchs may live as long as eight or nine months.
|Tagging instructions from Monarch Watch|
The monarchs’ arrival at the overwintering grounds typically coincides with Dia de los Muertos (November 1, Day of the Dead), an important fall festival in Mexico. Some locals apparently see the orange and black visitors as the spirits of their dear departed relatives, returning to celebrate the day. This is not as far-fetched as it may seem; throughout history humans have used butterflies as symbols of the soul and/or reincarnation. Did you know that the word “pysche” in ancient Greek meant both “butterfly” and “soul”?
But back to the present, and Houston. It was a beautiful afternoon so we all trooped outside, armed with nets, pens, data sheets, and numbered tags purchased in advance from Monarch Watch, a non-profit organization based at the University of Kansas that coordinates monitoring efforts. Soni also took a roll of scotch tape and some microscope slides. She is checking the butterflies for OE (short for Ophryocystis elektroscirrha), a sporozoan parasite. If present, the parasite spores can be seen under a compound microscope (they are much smaller than butterfly scales). If there are enough of them in a caterpillar’s body, these parasites can spell death for the butterfly. Luckily, parasite loads are typically low in migrating individuals – perhaps butterflies weakened by the parasites simply can’t make the long journey.
|Taking scale sample for OE test|
Lots of monarchs were coming around the corner of the Butterfly Center, dipping down to our outdoor butterfly garden and stopping to sip nectar from the blooms (they especially seemed to like wheat celosia and purple porter weed). Then they’d head off towards the Sam Houston statue and on in the direction of Rice University (southwest of us!). We caught 11 butterflies in the garden (and missed many more), tagged them (noting whether male or female), took a scale sample, and released them. Off they flew!
We’ll send in our data to Monarch Watch, and of course we hope that someone will find one or more of our tagged butterflies on the roost in Mexico. It is highly unlikely – given the millions of monarchs at the roost – but tagged butterflies (usually dead ones) do get found and reported. If one of ours is found, Monarch Watch will contact us – and they/we will know that butterflies do migrate to Mexico from our area.
Local butterfly gardeners know that a number of monarchs stay in Houston over the winter. We often don’t have killing freezes here, and the recent craze in butterfly gardening means that there is lots of Mexican Milkweed aka Butterfly Weed around. This plant, Asclepias curassavica, is a perennial from Central America; unlike our native milkweeds, it does not die back in the winter months. Also, predatory wasps, which take many caterpillars during the summer, are mostly gone – so if it doesn’t get too cold, Houston is a good place for monarchs to spend the winter. However, these butterflies are taking the risk of dying should we have a strong cold snap as we did last year.
Here are two great websites with information about these amazing butterflies and about how to get involved monitoring their migration: Monarch Watch at www.monarchwatch.org and Journey North at www.learner.org/jnorth/.