Cold Snap Raises Concern: How will the monarchs fare?


November 19, 2014
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Should I be concerned about the monarch butterfly?

Is it going extinct?

Will these cold temperatures kill the ones I’m raising?

What is “OE” and should I worry about it?

If you have questions about monarchs, you are in good company.

Thanks to the recent petition to US Fish and Wildlife by a number of conservation organizations to grant them “threatened” status, monarch butterflies have been in the news a lot this fall. Also, more and more people are hearing about the protozoan parasite that affects monarch health, the dreaded OE (short for the unpronounceable and unspellable “Ophryocystis elektroscirrha”). Finally, if you are in Houston, or other areas with monarch butterflies that do not migrate but spend the winter here, you may have questions about what this unusually early and unusually cold snap will have on the caterpillars and adults in your garden.

This is a quick response to all of those issues:

  1. Monarch butterflies are not in any sense endangered. The species is very widespread, found throughout the world, from Australia to southern Spain, Hawaii, etc., etc. What the groups petitioning for threatened status hope to achieve is to bring awareness to the possible end of the huge annual migration that takes place in the North American populations. Within the past decade or so, the number of individuals making the southern migration to overwintering grounds in Mexico has declined by about 90%. This is indeed worrying, and it would be a terrible loss if this unique and spectacular phenomenon ended. But there will still be monarchs – just not as many (millions instead of billions) and perhaps only non-migratory ones in areas where they can survive year-round. The decline in the North America population is thought to be due to a number of factors – the main one being loss of habitat. Genetically modified corn and soy beans have been bred to resist herbicides such as RoundUp, so farmers can spray their croplands for weeds (including milkweeds) and not affect these GMO crops. Until the widespread use of GMO crops, milkweed was abundant in the rows between plantings and in the highway right of ways.  Thus the huge expanse of farmland in the central USA cornbelt was critical in building up their populations during the breeding season (summer).  GMO crops, and subsidies for ethanol (which encourage corn farmers to plant every bit of their land, right up to the roadways) mean that this “cradle” of monarch populations is no longer available. There are other factors causing the huge decline in the migratory population – global climate change, urbanization, some habitat loss in Mexico – but this, i.e., habitat loss in the central USA, is the main factor. We do not know yet whether monarchs will be designated as “threatened” – such proposals take a long time to go through the various review processes. The good news is that this petition is raising awareness about this worrying loss of habitat – which affects not only monarchs, but bees, other butterflies, and many other organisms.

  1. “OE” is a naturally occurring protozoan parasite of monarch and queen butterflies (genus Danaus). This tiny organism multiplies inside the caterpillar stage, and is spread in a dormant spore form by the adult butterfly. Low levels of OE do not greatly affect their hosts, but parasite levels build up rapidly over successive generations of monarchs, and when infection levels are high, many detrimental effects (including death) are seen. Infected caterpillars may not pupate properly, or they may not be able to get out of the pupa, or the adults may be weak, malformed, or die early. Unfortunately, well-intentioned people raising successive generations of monarchs, especially on tropical milkweed (which does not have an annual dormant period) appear to be the main cause of OE buildup (via the very persistent spores).

    In areas like Houston, where mild temperatures allow for resident, non-migratory populations year-round, researchers have found that most adult butterflies are carrying the spores (i.e., over 75% of the butterflies they test are infected). For more information, visit the Monarch Watch organization’s website or click here for more information from the University of Georgia.

    You can also find plenty of information by doing an online search for Ophryocystis elektroscirrha.

  1. You raise monarchs and are concerned about whether they can survive the cold temperatures we’ve been having.

    The whole “point” of the monarch migration is to avoid cold temperatures – monarchs are really tropical butterflies that, like many songbirds, take advantage of our summers. However, in our area where it seldom gets truly cold, and where there is now lots of tropical milkweed available, thanks to the butterfly gardening craze, some monarchs forego the migration and spend the winter here, where they continue to breed (the migrating monarchs do not mate or lay eggs until spring). 

    Cold enough temperatures can certainly kill or harm monarchs, especially in the caterpillar stage or if they are in the process of pupating. However, unless it freezes and/or the caterpillars, pupae, or butterflies are highly exposed, monarchs can survive temperatures in the 30s. 

    During a cold snap, caterpillars will often crawl to the base of the milkweed they are eating and curl up on the ground until it warms up again. Adult butterflies can hunker down in a sheltered area and will come out again when it’s warm enough to fly. But if it’s cold enough for long enough, they will die. Of course it’s hard to tell people to let nature take its course — but that is probably best — especially given the high levels of OE we see in most people’s home-grown monarchs. If you do want to save your babies, you can always bring them inside for a few days until it warms up. 

    Butterflies can be fed sugar water, Gatorade, or fruit juice (place them with their feet touching a sponge or paper towel moistened with one of these sweet fluids and they will probably extend their proboscis to get a meal. If you would like to test to see if your butterflies have OE (only the adults can be tested), click here to learn how to do it. We (at the Cockrell Butterfly Center) would be happy to look at your samples, or you can send them to the University of Georgia.

If you have questions that were not answered here, feel free to write us at bfly-questions@hmns.org.

Nancy
Authored By Nancy Greig

Dr. Nancy Greig is the founding director of the Cockrell Butterfly Center, which she oversaw from 1994 to 2016. As emeritus director she continues to work with the museum doing outreach and education. Her academic training is in botany and entomology, with a specialty in the interaction between insects, especially butterflies, and plants. In addition to cultivating backyard butterflies, she grows vegetables and bees

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