1) Status of the Population
2) Monarch Tags
3) Temperature Monitoring Program
4) Monarch Watch Products
5) A Little-known Milkweed
6) Degree Days
7) Monarchs and Me
8) 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.
1) Status of the Population
I finished the “Status” section of the Update last month with the following statement. “The flow of monarchs through eastern Kansas in the second half of May this year has been the best I’ve observed since 2001.” This flow continued northward resulting in the largest number of monarchs reported to Journey North in the last 10 days of May since record keeping of spring sightings began in 1997. These reports were followed by numerous accounts of large numbers of eggs and then larvae especially in areas north of 43N latitude. Monarchs subsequently spread through the milkweed regions of the prairie provinces of Canada in unusually large numbers. Many observers declared that the monarchs were early for their region. Perhaps the butterflies did arrive early but I will make the case below that, relative to other years, they arrived on time. The only region in which monarchs were slow to arrive and might be deemed scarce was the northeast including the Canadian provinces of Quebec, New Brunswick and Nova Scotia. Thanks to Don Davis’s efforts and his many contacts in the provinces, there have been a number of reports of monarchs from eastern Canada for the last half of June. There is still time for monarchs to complete two generations in the northeast so low monarchs numbers now may not be a good indication of the fall migration in this region but, then again, it might well signal a low fall population. I’ll look in the crystal ball and will attempt to divine the future below. Let’s recap the spring and examine the monarch numbers over the last 6 weeks before we look ahead.
The spring sightings are summarized in Table 1. Once again we are indebted to Janis Lentz of Mercedes, Texas for summarizing the spring records from Journey North.
Table 1. Number of monarchs sightings recorded by Journey North for March through 15 June 2000-2006 and total number of hectares measured at overwintering sites in late December of the same year.
May 1-June 15 Totals Hectares
2006 109 51
673 - 2005* 31 42 90
398 5.91 2004* 34 35 64 179 312 2.19 2003 73 39 83 176 371 11.1 2002* 133 50 71
489 7.5 2001* 60 18 99
498 9.4 2000 61 27 109
*Years with relatively low numbers of butterflies returning from Mexico.
The first thing you might notice in this table is that the total observations (673) for the spring of 2006 is substantially greater than for all other years. This number alone might suggest a large fall population. However, we should dig deeper and ask whether there were conditions that facilitated such a large number of observations. In fact, there were. I don’t have the time to dig up all the details but if you watched the weather like I did this spring, I think you might agree with me that the weather facilitated the observation and reporting of spring monarchs. In the Midwest there were few extended periods of rain from April through early June and the weather was extraordinarily favorable as the monarchs were moving north from early to late May. Further, the weather in the northern states could not have been better in the last 10 days of May and the result was an abundance of sightings. The number of observers willing to report sightings has grown over the years and it is also the case that total sightings don’t seem to be especially effective in predicting the size of the fall migration and the overwintering population. For example, look at the similar totals for 2005 (398), 2003 (371), and 2000 (398) and yet the differences in the sizes of the overwintering populations, 5.91, 11.1 and 2.83 respectively. A better measure might be the May and June numbers.
As the overwintering monarchs move north through the southern states in the spring, the numbers dwindle with increasing distance and time such that by the end of April few, if any, of the overwintering butterflies are alive on the first of May. New adults, developed from the earliest eggs laid in Texas and elsewhere in the south, begin emerging at the end of April and start to move northward. The death of the spring migrants and the emergence of the new adults is such that after May 1st virtually all of the butterflies reported by observers are first generation offspring of the returning migrants. Surely, the number of monarchs reported from May 1st to June 15th is the next statistic we should look at as a possible predictor of the fall and winter numbers. Again, the number reported for 2006 (324) was high but was similar to 2001 (321). The population increased significantly in 2001 from that of the previous year (2.83 to 9.4) suggesting that there should be good numbers this year as well. However, before we get carried away, look at 2003 (179) and 2004 (176). Although the number of May-June observations were similar, in 2004 the population crashed and in 2003 the population grew. Even though it doesn’t appear that May-June sightings are useful predictors, the population this fall could be substantial, although there are still a few “ifs” as I will explain.
Although the monarchs appeared to be early this year to many observers, from my perspective it appears that they were on time. Generally, monarchs do not move north in a surge as they did this year. Rather, the arrival in the northern states is a trickle: the monarchs arrive but few observers are aware of them because of their low density. The result is that the monarch population is often off to a 10-15 day start before observers are aware that monarchs are in the area. The data in Figure 1 partially support my point. Note that the median day for all observations was the 27th of May. The mean of the medians for all years from 1997 through 2006 is 26 May. Looking at the data this way, it would seem that the northward movement of monarchs this spring was close to the long-term pattern. Early and late years deviate a week or more from the long-term mean of 26 May. In 2001, the year in which the spring numbers were most similar to those of this spring, the median for the spring observations was the 19th of May and in 2005 it was 2 June. The most unusual feature of the 2006 records is the pulse of sightings reported from the 24th through the 30th of May. Sixty-seven percent (218) of the sightings were reported in this 8 day period. There is no pulse of this magnitude for any of the years back through 1997. Note that the big day, the 27th of May, was a beautiful Saturday during a holiday weekend.
Figure 1. First sightings reported to Journey North from 1 May to 15 June 2006.
The number of reported first sightings usually decline significantly after the 1st of June. This year, June sightings were only 13% (41) of the reports for May- June. Last year was the exception. The median for the May-June reports in 2005 was 2 June and 59% of the first sightings were reported from 1-15 June.
The sharp pulse of sightings from 24-30 May 2006 is so unusual that it raises a few questions. Did the monarchs migrating during this period all originate from a narrow band of latitudes rather than all of Texas and part of Oklahoma? Or, was the weather so favorable that the butterflies moved in synchrony rather than being delayed in one region or another due to rain or wind, thus flattening the curve? I could make a case for both scenarios but I favor the first possibility. Here is my reasoning. In April I received two reports of large numbers of eggs being found on milkweeds in fields near Dallas. The reports were similar to the dumping of eggs I reported seeing in Kansas beginning on the 15th of April. Let’s suppose an egg was laid on a milkweed near Dallas on the 1st of April. Given the subsequent temperatures and monarch degree days in the Dallas area (see below) a new adult monarch could have emerged from a pupa on the 7-8th of May. Let’s suppose that at least two days are required before this monarch can begin to move northward so the flight begins late on the 10th of May with the real movement beginning on the 11th. The next question is: how long would it take this butterfly to reach the northern breeding grounds? An analysis David Gibo and I conducted in 2000 showed that the first generation monarchs appear to move northward at a rate of 55 miles per day, the fastest rate of spread of the population during the entire annual cycle. At 55 miles per day, our Dallas butterfly might be expected to pass through Lawrence, Kansas on 18 May, through Des Moines, Iowa on 22 May and St Paul, Minnesota on 26 May. This scenario fits remarkably well with reported sightings. As reported in the last Update, I first started seeing monarchs moving through Lawrence on the 19th of May and Gene Tiser and a colleague found tens of dead monarchs washed up on the western shore of Lake Michigan on the 26th. I could extend this analysis but the point is that the pulse, and therefore the timing of the arrival of monarchs in the northern states, is consistent with the hypothesis that most of the monarchs reaching the north originated from eggs laid in the last week of March to early April in central and northern Texas and perhaps into southern Oklahoma. This scenario is also consistent with the rate of monarch development as predicted from monarch degree day calculations (see Dallas DDs below).
The pulse of monarchs this spring and the large number of instances in which observers reported finding numerous eggs in the last few months raises another little studied issue “realized fecundity”. Monarch females have the capacity to produce 400-1000 eggs. There is variation in egg laying among females due to size and larval nutrition that determines the size of the fat body upon emergence. (The fat body has a role in the mobilization of nutrients incorporated into eggs). Nevertheless, the potential egg production per females is quite high. Whether monarch females are able to maximize this fecundity is dependent on many factors. Extreme temperatures, high winds and rainfall all impede egg laying and can reduce realized lifetime fecundity because the butterfly ages even though it is unable to lay eggs. As with development of immature stages, the longevity of adult monarchs is defined by degree days. According to Myron Zalucki, the adult reproductive monarch has the capacity to live 750 F degree days. At an average of 10 DDs/day we might expect and adult monarch to live 75 days and at 15 DDs/day 50 days and so on. It follows that at higher temperatures females have fewer days in which to maximize the number of eggs laid. At the peak of egg laying, females are laying about 40 eggs a day. However, if they can’t lay eggs for two days this doesn’t mean they can lay 120 eggs on the third day simply because the monarch reproductive system matures eggs in sequence and does not have the capacity to retain 120 fully developed eggs. Consequently, there is a reduction in realized lifetime fecundity for every day during which egg laying is impeded. This season appears to be one in which the spring monarchs were able to maximize their fecundity.
Given the large number of monarchs that arrived in the northern breeding grounds, and the subsequent numerous reports of large numbers of eggs and larvae, the prospects for a large fall migration in the Midwest seem to be excellent. I have reservations about the northeast and am willing to predict that the number of monarchs passing through Cape May and along the Atlantic coast will be relatively low this fall.
There is still a long time from these thoughts in late June to the late August-September migration and there are a number of factors that could lower the prospective fall population. I can think of six factors that might reduce the population, perhaps you can think of others. My six are: 1. drought 2. predators and parasites 3. extremely high temperatures (>100 F) 4. extremely low temperatures 5. long periods of rainy weather during peak egg laying periods, 6. senescent milkweeds.
1. A visit to Drought Monitor shows that the drought is spreading to the north and east. Droughts limit the availability of water and nectar and therefore the longevity and fecundity of the butterflies. Low soil moisture also reduces the growth rate for the milkweeds, possibly changing the quality of the leaves available to the monarch larvae. The most recent drought report contains good news and bad news. The good news is that the conditions in the mid Pacific that lead to a La Nina event, one of whose effects is to create droughts in the SW states that extend into the western Midwest, are fading. The bad news is that the return to normal rainfall for the region may not happen for several months.
2. Predators and parasites could make a difference. The arrival of large numbers of egg laying monarchs creates and early summer source of food for those invertebrate predators and parasites that feed on monarchs. As with other creatures, their population growth is enhanced by an abundance of resources in the form of monarch larvae. Growth in the populations of these species could result in significant losses of monarch eggs and larvae in the last generation.
3. Extremely high temperatures not only reduce the longevity and realized fecundity of adults but appear to take a toll on larvae in the upper Midwest. The upper developmental zero is 91.4F for monarchs, meaning that growth of monarch larvae stops at these temperatures. Daily temperatures that reach the 90s and 100s reduce the growth rate of larvae, exposing them to predators for longer periods, and can even kill them if the temperature increases are sudden.
4. Extreme low temperatures at the wrong time could impede egg laying, lengthen larval development and reduce the number of monarch generations as it did in 2004.
5. Rainy weather could also reduce egg laying and have a significant impact on the number of monarchs in the last generation. The 10 days of rainy weather from Virginia to upstate New York from mid to late June almost certainly had a negative impact on monarchs in that area.
6. The condition of the common milkweeds for the monarch larvae maturing in late July and August could also have an impact on the population. If the plants are senescent, as they generally are in eastern Kansas at the end of the season, egg laying will decline and the nutritional value of the leaves to the larvae could be reduced.
I’ll be watching for all these factors in the coming months but I could use your help. Let me know what you see.
2) Monarch Tags
The monarch tags for the 2006 tagging season have arrived and they look great. We will assemble the tagging kits and begin shipping tags the first week of August to everyone that has already ordered them. We have limited the number of tags for distribution this year to 190,000 - down from the 300,000 we have issued in the past. Given the large migration we expect this year, it would seem to make sense to distribute more tags. However, the reality is that more tags means more recoveries in Mexico and we simply haven’t been able to raise enough money through the Tag Recovery Fund or other enterprises to pay for the large number of tags we have been recovering in Mexico. The catastrophic mortality due to the winter storms in the winters of 2002 and 2004 resulted in an enormous number of recoveries and some extraordinary data but has devastated us financially. Unfortunately, we are in a hole that will only get deeper if we issue a large number of tags that result in recoveries in Mexico that we can’t afford to pay for.
You can see where I’m going can’t you? Please order all of your tags now or you may not be able to get tags at all. When we are out of tags, that’s it. I’m afraid the limited number of tags will mean that some taggers will be disappointed this year. We apologize in advance, but we just can’t afford the costs associated with issuing more tags. We don’t make any money on the tagging kits and we are actually losing money if we account for all the time and resources associated with this program. The costs of the tagging kits include order processing, shipping, handling, recording all the tag codes per order, processing the data sheets (thousands), entering all the tagging data (up to 100,000 records per year) into a database, as well as collating all the recoveries. Additional costs are associated with each recovery for which we have not received the datasheet since this involves trying to track down the missing data. The proportion of recoveries for which we don’t receive data sheets has increased from around 10% to nearly 25% last year. It is very discouraging to buy tags, about a thousand dollars worth last year, for which there is no data. It’s money wasted. If you tag, please, please, please send us your datasheets.
Tagging Kits are available via the Monarch Watch Shop at
or by calling 1-800-780-9986.
3) Temperature Monitoring Program
Thank you for your interest in our new temperature monitoring program! The response to our brief announcement a few weeks ago has been somewhat overwhelming and we have decided to move forward with the development of this new program in two stages. First, we will select 50 sites to participate in our initial beta testing that will last 1-2 months. Once we have the bugs worked out (perhaps as early as September) we will invite all of you that have emailed us thus far to participate at whichever level you decide - with a full monitoring kit that will include everything you'll need to interact with the temperature loggers or with a "lite" kit that will only include the temperature loggers that you will mail back to us when it comes time to download the data you collect. We have many ideas for projects based on this program in addition to monarch degree day calculations - details will be available soon.
We have several goals for this program. One goal is to develop a thorough understanding of the growth of monarch populations in all portions of the country. To achieve this objective we need a network of participants who will monitor temperatures in monarch larval habitats. Our attempts to document the growth of monarch populations by monitoring degree days, while revealing, has several failings. First, the degree days are calculated from temperatures measured at 1.5 meters at weather stations that are some distance from the observed larvae. Secondly, the estimating method we are using to calculate the degree days is known to have limitations. Thirdly, since monarch larvae appear to have some control of their body temperatures by exposing themselves to sunlight, they would appear to have the capacity to develop faster than would be indicated by simply measuring degree days. Our temperature loggers can help us resolve each of these problems. The loggers will allow all of us to obtain data at the site where larvae are developing rather than using temperatures from remove sites. We will also be able to calculate degree days more accurately by using hourly temperature measurements and we will be able to enlist volunteers and students to conduct numerous experiments that will reveal the extent to which larvae use the heating of the sun to shorten their development. And then, there are all of the other applications and lessons that are possible using this technology.
Those participating in the beta testing will receive a prototype kit containing temperature loggers, readers, instructions, etc. and will assist us in developing the protocol for placement of the loggers in monarch habitats and data retrieval/analysis. We will facilitate communication by setting up an online forum dedicated to this project and everyone is invited to join in to provide feedback and ask questions. Stay Tuned!
4) Monarch Watch Products
Seed Kit Sale
We need you to do us a favor. We overestimated the number of Monarch Waystation seed kits we needed this year and we would like to move the overstock out of inventory. We have reduced the price of the kits from $16 to $12 (that’s only $1 per seed pack). Yes, we know it is too late to plant the seeds this year but if you buy the kit now as a present for a friend or relative, or a group you wish to support, you can put the kit in the refrigerator and the seeds will be good for next spring. To purchase the seed kits (Item #125522) please visit
or call 1-800-780-9986.
Monarch Rearing Kits
As you may or may not know, we provide monarch caterpillars so that you can raise monarchs at home or in the classroom. The demand for these kits is extremely high from mid-August to October; however, they are available now as well. If you want to assure that you or your school will receive a kit during a particular week, please place your order now so that we can match the production of eggs and larvae with demand. To purchase a monarch rearing kit (item #113232) please visit
The kit contains fourteen to sixteen first to third instar monarch larvae (caterpillars) and rearing instructions. The larvae arrive in small cups and must be transferred to milkweed plants or leaves to feed. Please make sure you have fresh milkweed available before your caterpillars arrive. Each caterpillar generally needs 18 inches of milkweed to pupate. Pupation will occur in about 10 days and adults will emerge 10-14 days after pupation. These butterflies can be used for classroom instruction, student projects or to start a classroom breeding population.
Pupa Kits in August and September
Those of you who do not have access to milkweed but still wish to experience part of the monarch life history will be able to purchase pupa kits (containing 4 monarch pupae) in August and September.
5) A Little-known Milkweed
Asclepias exaltata Poke Milkweed
Curt Lehman encountered a milkweed new to him in western Pennsylvania and sent us some fine images to help him identify the plant. He was biking on Allegheny River Trail in Venango County south of Franklin, PA when he encountered the mystery plant. The species in question is the little known poke milkweed, Asclepias exaltata. It is one of the few milkweeds that’s relatively shade adapted and it is often found on the edge of woods or within partially open glades in forested areas. In my experience, the patches of this species are relatively small and often isolated like those of one of the other shade tolerant milkweed species, the purple milkweed, Asclepias purpurascens. The poke milkweed is said to be a good host for monarchs and is available from some nurseries.
Distribution of the poke milkweed, Asclepias exaltata in the United States.
6) Degree Days
Once again we will follow the monarch degree days through the season for five cities from Dallas to Winnipeg (Table 2) 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 2. Degree Days (F) Running totals starting on average, or observed, dates of first monarch arrivals in each city*.
Date Dallas Lawrence Des Moines St. Paul Winnipeg
*Winnipeg, Manitoba (Canada) 49:54:00N 97:07:48W, St. Paul, MN 44:56:52N 93:06:13W, Des Moines, IA 41:34:36N 93:37:03W, Lawrence, KS 38:57:46N 95:15:19W, Dallas, TX 32:47:39N 96:45:55W.
The accumulated degree days for each city for the last 4 years is shown in Table 3. A glance at these data shows how this year compares to the others and leaves no doubt that we are having a warm to hot year. Look at Dallas! The number of monarch degree days this year is almost 300 DDs ahead of last year; even Winnipeg is 143 DDs ahead of 2005, a warm year for that location.
As you may recall from the headlines, last year was heralded as the warmest year on record for the planet. We are setting all sorts of records this year as well since both January and April produced the highest average temperatures in the United States in the 110 years that these statistics have been kept. As pointed out above, warmer weather will increase the number of monarch generations but it could have a number of negative impacts on the population.
Table 3. Monarch degree day totals and potential number of generations through 20 June for 2003-2006.
Year Dallas Lawrence Des Moines St. Paul Winnipeg 2003 1749.1/2.4 712.8/.9
168.0/.2 2004 1762.2/2.4 914.2/1.3 709.2/.9
96.7/.1 2005 1727.3/2.4 816.6/1.1 671.3/.9 454.8/.6 157.4/.2 2006 2001.7/2.8 1044.5/1.4 834.7/1.2 579.8/.8 290.2/.4
7) Monarchs and Me
by Sondra Cabell, Naturalist, Buchanan County Conservation Board, Hazleton, Iowa
This past March 4-11 I was able to fulfill a longtime dream of mine I went to Michoacan, Mexico to see the overwintering sites of the Monarch Butterflies. This was a chance for me to further understand an animal that has had a major role in my life.
As a child growing up in Iowa, I remember seeing huge clusters of monarchs on the pine trees at my grandparents’ farm and at the town park. This memory resurfaced after graduating from college.
During the summer of 1987, not yet knowing what I wanted to do with my brand new bachelor’s degree in biology, I attended graduate classes at the University of Michigan Biological Station. I took two classes entomology and field photography. When working on my photography project, I thought why not combine the two and do my photography of insects.
While in the field collecting, I would take my camera and get photos as well. It was while attempting to take photos of a monarch butterfly, that I realized she was laying eggs. And I was able to get photos of the egg starkly contrasted on a bright flower bud.
That did it most of the rest of my photos were on the development of the monarch I harvested the egg, and took photos of the caterpillar as it grew, the chrysalis and the adult. I missed the formation of the chrysalis and the emergence of the adult, but I still had all the stages and a great photography project. My photography instructor, Gary Williams, (not my entomology prof) informed me that I was still missing part of the story. He introduced me to the monarch migration which I may have known in the abstract and tagging monarchs.
As a high school teacher, he had tagged monarchs through Fred Urquart’s program at the University of Toronto. I learned how to hold the monarch and carefully remove the scales along the inside and outside of the leading edge of the upper wing. Then a small rectangular tag was placed on one side, folded over and pressed tightly to both sides of the wing. The tag number and location of release were recorded and the butterfly was released (after being photographed, of course).
I was hooked! I took several additional tags with me at the time (tags were not so numerous as to be assigned each year) and used them over the next several years in Georgia, South Carolina and Kentucky as my travels and career as an environmental educator took flight.
While in Kentucky, I became aware of the tagging now being done through the University of Kansas and signed on to tag with that program. Being a new tagger to their program, and one in Kentucky where they had not yet had a recovery in Mexico I signed on to become a coordinator for the state. In 1995, I tagged for the Monarch Watch program for the first time. It wasn’t until the 1998 tagging season that I would have a recovery not in Mexico, but in Lindsborg, KS. That butterfly had traveled 546 miles (straight line) in 20 days.
The following year, I had a recovery in Mexico one of the first ever recorded from Kentucky (there were 3 that year). And last spring, I had a tag from 1997 my first butterfly to make it to Mexico and be found was reported 7 years later. Talk about delayed gratification!!
I moved back to Iowa in 2001 and tagged more butterflies that fall than I was able to in Kentucky there are many more monarchs that are in or fly through Iowa. Of course, that winter was one of the worst kills in Mexico and in just one season, I had 13 new recoveries. I now have 29 and counting from butterflies tagged in 2001.
In addition to tagging, I have raised thousands of caterpillars in the nature centers where I have worked, learning about parasitism and other perils along the way. Every summer, the caterpillars and chrysalids are one of the favorite displays for all ages.
In 2004 I was able to attend a training for the Monarch Larvae Monitoring project and now have volunteers trained to monitor the areas at our nature center and at my home garden. I have learned a tremendous amount about the growth and changes in the larval stages.
But the missing stage in the monarch life cycle for me was seeing the overwintering areas. I had, of course seen pictures and even had an intern who worked for me travel and see the colonies while she was in Mexico. Nothing can describe the spectacle, so I won’t even try. But if you ever have the opportunity, don’t pass it up; you will remember it for the rest of your life.
During my visit I wanted the opportunity to support the local communities. I brought several Spanish language children’s books for the school we toured. I have a mug bought from a woman whose clay covered hands told me she made the pottery herself, and a pine needle barrette, but I couldn’t find any earrings. So, I made arrangements to have some earring hooks sent to crafters in the Cerro Pelon area. We rented horses at Cerro Pelon, and I was able to complete my personal tagging experience by buying some tags from the guides there.
As much as I have worked with and learned about monarchs, to me the true marvel of these animals remains in their mystery. How do they get back to the same areas so exactly that at El Rosario they have a paved trail through the colony? How does that caterpillar ever get rearranged inside the chrysalis to become the butterfly? I might be happy to never know these answers. But I can’t help but ask about the questions that remain. And I will continue to be involved with those programs working to find the answers.
8) 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.
Previous updates are available online at
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Thank you for your continued interest and support!
Monarch Watch (888) TAGGING - or - (785) 864-4441