Monarch Watch Update - August 2006



1) Status of the Population

2) Fall Open House

3) Monarch Waystations

4) Weed Control in Pastures

5) Cool Cats

6) Air Fresheners: A Possible Hazard for Monarch Caterpillars

7) Milkweed Seeds – Vernalization and Scarification

8) Degree Days

9) About Monarch Watch


Unless otherwise noted, all content was authored by Chip Taylor, edited by Jim Lovett, and Ann Ryan and published by Jim Lovett.


My apologies for the lateness of this Update. My only time to write these Updates is on weekends and my last 5 weekends have been occupied with other Monarch Watch activities. - Chip

1) Status of the Population

It has been an up and down summer. If you have been following the Updates, you may recall that the number of first generation monarchs that moved north from Texas, Oklahoma and southern Kansas, as well as other areas in the south eastern states, in late April through early June was nothing short of spectacular. From my perspective as one who receives reports from many correspondents, in addition to those sent to Dplex-L and Journey North, the size of the first generation was certainly the highest in the 14 years I’ve been following the spring migration. The surge of monarchs northward resulted in some unusual sightings such as substantial numbers of spring monarchs being washed up on the shores of Lake Michigan after a storm. Such events are uncommon but, prior to this report, I had only heard of fall monarchs being washed ashore.

The number of monarchs moving north in May and June produced reports of monarchs from eight Canadian provinces including some sightings in which monarchs appeared to be well beyond the known distribution of milkweeds. In fact, Don Davis received one report of a monarch being sighted in Newfoundland!

The large first generation encountered favorable conditions over much of the northern breeding range resulting in many claims that the observers had never seen so many larvae in late June and early July. Larvae seemed to be everywhere with many people finding 2-3 larvae “on every plant”. Large numbers of these larvae reached the adult stage in mid to late July just in time to mate and lay the eggs that would develop into the butterflies of the migratory generation in mid to late August. However, the ability of the mostly second generation monarchs to give rise to a large migratory generation evidently varied greatly across the country. The critical egg laying period to produce adults of the last generation varies with latitude but usually encompasses the last two weeks of July and the first week of August. Broadly speaking, the conditions for reproduction were favorable in the East and much less favorable in the upper Midwest, one of the traditional monarch breeding hotspots. The drought monitor map for 1 August (Figure1) provides a possible explanation. July was extremely dry in the eastern Dakotas, Minnesota, and into central Wisconsin. In addition, the temperatures were much higher than normal for much of this area in July and early August. These conditions apparently decreased the “realized fecundity” of the last generation with the result that one tagger declared that the population moving through southern Minnesota was the lowest in the last 11 years. In contrast to most years, there have been no reports of large clusters of monarchs in the Dakotas, northern and western Minnesota, Wisconsin or Iowa, the exception being one sighting of a large cluster in southern Minnesota.

Figure 1.

So, why might a drought cause the population in the upper Midwest to decline? There are several possibilities but here is a plausible scenario: 1. a drought reduces the availability of water and nectar needed by the adults for reproduction causing some females to die without laying the normal number of eggs, 2. higher temperatures result in higher metabolic rates, increasing the demand for carbohydrates (sugars) (perhaps even diverting some of the carbohydrates converted from fats that would normally be used in egg production to meet metabolic needs), and reduced longevity. 3. drought results in a rapid decline in the quality of the milkweeds and since females prefer to lay eggs on milkweeds with new growth, the search time (and distance) between egglaying events increases resulting in fewer eggs laid per female. 4. survival of young larvae on senescing milkweeds might well be lower than on plants with newer leaves.

Conditions were consistently better throughout the eastern breeding area, i.e. east of central Wisconsin, and the number of migrating monarchs appears to be high in many regions yet not as high as I was expecting based on the reports of the second generation. Was the last generation somehow downsized in the East or were my expectations too high? I’m not sure. The information from the East is too fragmentary and there are no relative measures yet with which to compare this year’s migration with those of previous seasons.

Fragmentary information or not, it’s time for me to stick my neck out and predict the size of the overwintering population – with the stipulation that I have the opportunity to revise my predictions as more information becomes available over the next 8 weeks. Before I give my prediction I should mention that another factor under consideration is the drought in Texas and northern Mexico. Texas has been experiencing what some have characterized as a 50-year drought – meaning the kind of drought that only occurs once in 50 years. The conditions in northern Mexico are similar to those in Texas. At this writing (10 September) it would appear that the migratory population will encounter drought conditions for more that 1000 miles as it moves through Texas and northern Mexico (Figure 2). The lack of water and nectar on this route could take a significant toll on the monarchs.

Figure 2.

I’ve been predicting the size of the overwintering population for a number of years. No one has commented on my prognostications leading me to believe that 1) no one reads the predictions 2) no one cares about my speculations 3) I’m regarded as delusional so it doesn’t matter what I say or 4) you are all very kind and don’t want to hurt my feelings by pointing out how wrong I’ve been. Knowing I could count on Janis Lentz to tell me how wrong I’ve been in the past, I asked her to scan and assemble my predictions over the years. The predictions from 1999 through 2005 are shown in Table 1.

Table 1. Predicted and measured number of hectares at the overwintering sites in Mexico. The predictions are based on assessments of the summer populations and the strength of the migration.

Year Predicted Actual
1999 10








2002 5, then 3-4 7.5
2003 >7.5 11.1
2004 4-6, then <4, then lower than 2000 2.17
2005 5-7, then 7-9 5.92

Depending on your perspective, my predictions are either pretty good or quite poor. For the years 1999, 2001, and 2005 my predicted number of hectares is fairly close (roughly within a hectare) to the number measured at the overwintering colonies in December of that year. In 2000 the final population was only 2.83 hectares, less than half of the 6 hectares I had predicted. In 2002 I underestimated the size of the population by almost half. My pronouncements were less precise in 2003 but I correctly predicted that the population would be bigger than in the previous year. All the indications throughout 2004 were in the direction of a low overwintering population, and at the end of the migration I declared that the overwintering population might well be the lowest in the last 14 years and therefore lower than the 2.83 hectares measured in 2000. The final population for 2004 was indeed the lowest ever measured, a mere 2.17 hectares. Overall, it looks like my predictions were reasonably close to the measured number of hectares in 4 of the 7 years.

Ok, so how about 2006? My preliminary estimate is 5.5 hectares. If the there are rains in Oklahoma, Texas, and northern Mexico over the next 6 weeks, I’ll increase the estimate by at least 1 hectare and if there are indications of large numbers of monarchs moving through Michigan, Illinois, Indiana, and Ohio, in the next two weeks, I may go even higher. In July I had high expectations and was thinking of an overwintering population of 12 hectares or better but I have been down sizing my estimate ever since visiting Minnesota in the fourth week of August. The high numbers of monarchs seen in June and July for the western part of the northern breeding range has not resulted in the expected high number of migrants, perhaps due to the drought, and this region is a major contributor to the overwintering population. The number of migrants reported thus far from the eastern portion of the breeding range is also lower than expected but it’s still early in the season. I’ll have a revised estimate in the September Update.


2) Fall Open House

Each year we celebrate the arrival of the monarch migration from the north on the second Saturday in September with an Open House at our facility in Foley Hall on West Campus at the University of Kansas. The Open House (9 September) was a great success. We attracted at least 500 visitors and ran out of cookies and pupae. Our visitors enjoyed 40 dozen cookies along with at least 20 gallons of lemonade and we gave away over 360 pupae to the children (and more than a few adults) who visited the pupa tent.

Outside the building visitors enjoyed the spectacularly robust and enthusiastic butterfly and pollinator garden created by Master Gardener Margarete Johnson, stopped to see the monarchs and other butterflies in the “Biohouse” (our butterfly vivarium), participated in a caterpillar hunt with the help of Jackie Goetz, and watched and listened as I gave demonstrations of monarch tagging. Inside Foley Hall our visitors viewed our monarch production cages, watched the critter crew prepare kits for schools, learned about honey bees while watching our observation hive, marveled at live ant lions, spiders and other unusual insects, and watched videos of monarchs and killer bees. Many also videochatted with Janis Lentz from Mercedes, Texas. Janis was kind enough to spend much of her day talking to children, and many adults, about monarchs via iChat videoconferencing.

I enjoy these events. It gives us an opportunity to reach out to the local community but I’ve been particularly gratified by the effort made by many Monarch Watchers to attend these events. Our visitors came from many distant locations in Kansas, from Nebraska, Missouri, Iowa, South Dakota and, because she was in the area, Jenny Singleton from Grapevine, Texas stopped by. Jenny has been with Monarch Watch since she saw our first call for volunteers to tag monarchs in her local paper in 1992! A check of the tag recovery database shows that Jenny has had 33 of her tagged butterflies recovered with 26 of those tags being recovered in Mexico. Thank you for your continued support Jenny!


3) Monarch Waystations

Headed for 1,000

The number of Monarch Waystations is approaching 1,000 – there are currently more than 900 certified and registered Monarch Waystations and the number increases each week. It would be extraordinary to reach this next milestone before the end of the year - let’s make that our collective goal. Please urge others to register their monarch habitats. We need publicity to keep this valuable program going and it always helps when Monarch Watchers have their interest in monarchs and monarch conservation featured in local papers.

Complete information amnd promotional materials are available at

Monarch Waystations in Cleveland

The following article by Carly Martin describes Monarch Waystations created within the Cleveland Metroparks system. These Monarch Waystations are a wonderful example of how municipalities can assist in the creation of monarch habitats while educating the public about monarch biology and conservation.

Cleveland Metroparks Monarch Waystations
by Carly Martin, Cleveland Metroparks Naturalist

Cleveland Metroparks is very pleased to have joined in Monarch Watch’s Monarch Waystation program. Our Outdoor Education staff has teamed up with Park Maintenance and even horticulturists from the Cleveland Metroparks Zoo to create nine Monarch Waystations this year. More are planned to be added in 2007, along with nature center programming which will help others build Monarch Waystations in their yards at home.

Cleveland Metroparks features over 20,000 acres of parklands, surrounding Cleveland like an Emerald Necklace of green, with 16 park reservations. Visitors can travel by foot, bike or car along parkways that connect many of the reservations. In a way these reservations are like waystations for all of us. It seems a natural next step to join a project creating habitat waystations for what may be the world’s most remarkable insect, the monarch butterfly.

The nine Monarch Waystations found in Cleveland Metroparks are each unique. They include nature center gardens, managed meadows, zoo landscaping, a restored prairie and (my favorite) a garden located in the grass island of a large parking lot. Each is a different size, is managed differently, contains different plants and has a different team of staff members supporting it. Yet, they are all great monarch habitat. Every one was home to monarch caterpillars and visited by adults this summer.

Along with maintaining the waystations our nature centers have created monarch exhibits and our naturalists have added extra monarch programs to our summer schedule. Our EarthWords Nature shop even joined in by selling a ready-to-plant assortment of seeds or root-stock that would grow well in northeast Ohio to create a monarch garden.

Cleveland Metroparks South Chagrin Reservation, The Shelterhouse Waystation:

Monarch Waystation #1: More Photos

Another series of photos taken in Monarch Waystation #1 is available for viewing at


4) Weed Control in Pastures

One of the aspects of monarchs and milkweeds that I have not been able to obtain data on is the number of acres of grazing land that are sprayed each year to control invasive or even native weeds, brush or trees. My perception was that milkweeds would be lost from these landscapes as a result of such spraying but it didn’t occur to me that they could be the primary reason to initiate spraying.

Gary Stell sent a message to Dplex-L containing a link to an article indicating that indeed this can sometimes be the case:

The article touts the value of a product named “Surmount” for the control of green milkweed, Asclepias viridis. I posted a note to Dplex-L that included the following points: 1) cattle avoid eating A. viridis, 2) due to the fact that this plant senesces in the heat of the summer, it does not compete significantly with grasses for space, nutrients or water, 3) this species is the main host of first generation monarchs in Texas and Oklahoma and that without this plant the size of the first generation monarchs moving north in late April and May would be much smaller. Subsequently, two of the frequent contributors to Dplex-L, Jacqui Knight and Carol Culler, submitted letters to the North Texas e-News, the source of the original article:

Clearly, we need to conduct more research to fully understand the impact of the use of herbicides on milkweeds and monarchs. However, although we don’t really need it, we have yet another justification for emphasizing the need to protect monarch habitats and to create Monarch Waystations.


5) Cool Cats

Lisa Conrad sent us a photo of an unusual caterpillar found by one of her students, Collin Bice of Waterloo, Indiana. Lisa has been very active in promoting monarchs and has succeeded in getting the town council to declare the monarch the town insect and the town as a Butterfly Sanctuary. Lisa and her students have lobbied the legislature in Indiana two years ago to have the monarch declared the state insect and they are gearing up to try again. The school courtyard is a Monarch Waystation.

More cool cats...

Watermelon is associated with the heat of summer for me – a cool refreshing desert to finish off a picnic or to end a summer day. Evidently monarch caterpillars feel the same way.

This image was received from Winnie Silk (Monarch Waystation # 281) who wrote “I had put some watermelon rinds in my cages to feed the butterflies that I could not release because of the tropical storm that was passing through our area. I was amazed to see the caterpillars eating the rind even though there were milkweed leaves right next to them. I thought the Monarch would only eat milkweed!!

I will comment on this behavior in detail in a future update.


6) Air Fresheners: A Possible Hazard for Monarch Caterpillars

We received the following communication from Sheryl Lynch concerning the possibility that air fresheners may contribute to larval mortality when used near rearing containers.

“I had a devastating experience last year with the monarch caterpillars I was rearing in my kitchen, and I wanted to share it so others would be aware of how fatal plug-in type air fresheners can be.

I had my caterpillars in a fish tank on the kitchen counter, under the overhead cabinets with under-cabinet fluorescent lights. Nearby I had a plug-in type air freshener which, when the strong scent magnified in the heat from the lights, killed many of the caterpillars. At first I thought I had poisoned milkweed, strange bugs, I couldn't pinpoint why my caterpillars were dying, and it turned out to be the air freshener.

I hope you can alert others to this danger, our monarchs are too precious to lose!!!”

If anyone has had similar experiences, please let us know.


7) Milkweed Seeds: Vernalization and Scarification

We received an interesting tip (edited) from Joseph McCulloch of Normandale Community College in Bloomington, MN.

“My students collected common milkweed, a cultivated milkweed, orange milkweed, prairie and swamp milkweed seeds in late fall. Seeds were placed in labeled 1 gallon zip-lock bags with a slightly moistened paper towel and placed in a refrigerator from late November until mid April. In mid April, my Ecology and Evolution students opened the bags, removed the moist towel, let the seeds/dry out for about 1 hour, then added two to three 2 inch squares of sandpaper to each bag and shook vigorously for a few minutes to scarify the seeds. We then planted the seeds in flats, one species/flat and placed the flats under lights in our plant room. Germination was approximately 90% in all species. After 4 weeks the flats were transferred to our temperature room in the greenhouse and then “hardened” outdoors for two weeks on the west side of the greenhouse, a site that is partially shaded in the afternoon, before transplanting the seedlings to the gardens.”


8) Degree Days

We have been following the monarch degree days through the season for five cities from Dallas to Winnipeg (Table 1) to get a sense of the environment experienced by monarchs in different regions and to be able to compare one season with another.

Monarchs require 720 degree days to complete development from egg to egg, that is, from the time an egg is laid until a female has mated and laid her first egg. Dividing the accumulated degree days by 720 for each site gives us a way of estimating the number of monarch generations at different latitudes. At high temperatures these degree days accumulate rapidly and development can be completed in as little as 24 days. At cooler temperatures, degree days accumulate over a longer interval and generation lengths can increase to 40 and even 50 days, thus reducing the potential number of generations per season. Further, an increase in generation length has the effect of exposing the larvae for longer periods to predators, parasites and other environmental hazards that could reduce the proportion of the larvae reaching the adult stage. The formula used to calculate degree days is presented in the “Teaching with Monarchs” article in the January 2005 Update. The formula is quite easy to use. Give it a try. We are using a “modified averaging method” for calculating degree days. This method is the one most commonly used to predict the development of organisms.

Table 1. Monarch degree day totals and potential number of generations through 25 August for 2003-2006.

Year Dallas Lawrence Des Moines St. Paul Winnipeg
2003 3804.9/5.3

















2006 4089.8/5.7 2593.4/3.6 2417.2/3.4 2074.3/2.9 1396.9/1.9

We all know it has been a hot year starting with the warmest January since temperature records have been kept for the entire United States. Warmer than normal conditions continued through the spring and summer. A quick glance at Table 1 shows that the number of monarch degree days through 25 August was greater in 2006 for all five cities than for the previous three years. Greater numbers of generations have the potential to increase the size of the fall migration. However, other conditions also have to be favorable. Unfortunately, the drought and the high temperatures in July and early August appear to have trumped any advantage due to a greater number of generations in the upper Midwest.

If you have been following these degree day ramblings, you may remember that the method we are using to calculate degree days is based on a laboratory model developed by Meron Zalucki. The model is excellent, however, the application of temperature data from official weather stations (where the temperature is recorded at 1.5 meters rather than at .5 meters, where most monarch larvae are found) clearly underestimates the number of generations. This realization has led to the use of temperature data loggers as a way of more accurately recording the thermal environment experienced by developing monarch larvae. As mentioned above, these devices are now being beta tested. Our intention is to have this product available for all Monarchs Watchers, and for schools, for the start of the season next year.


9) About Monarch Watch

Monarch Watch is a not-for-profit educational outreach program based at the University of Kansas. We manage several educational, conservation and research programs - focusing on the monarch butterfly, its habitat and the spectacular fall monarch migration.

We rely on private contributions to support the program and we need your help! Please consider making a tax-deductible donation. Complete details are available at or you can simply call 800-444-4201 (KU Endowment Association) for more information about giving to Monarch Watch.

Previous updates are available online at

If you have any questions about this email or any of our programs please feel free to contact us anytime.

Thank you for your continued interest and support!

Monarch Watch

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