Monarch Watch Update - August 21, 2003



1) Welcome!

2) Status of the Population

3) 2003 Membership/Tagging Kits

4) Peak Migration Dates

5) Upcoming Monarch Events

6) Tachinid Update

7) Imaginal Discs

8) Rearing Containers

9) How to Unsubscribe from this Update


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2) Status of the Population - by Chip Taylor

I’ve been optimistic about the prospects for the coming fall migration since our visit to the Mexican overwintering sites in March. The size of the migratory populations should approach or exceed those seen in 1999 and 2001, the two largest populations since 1996. If I’m correct, this will be one of our better tagging seasons.

Conditions for Breeding

Each year at this time I point out that for the northern breeding range, i.e. >39 degrees N, it is the eggs laid by female monarchs in the last two week of July and the first week of August that mature to become the migratory adults a month later. The size of the migratory population is determined principally by the number of eggs laid during this interval and the conditions encountered by the larvae that determine the survival of the immature stages. A check of the drought monitor

shows that abnormally dry conditions are increasing in Kansas, Nebraska, Oklahoma and northern Texas. Since these are not major breeding areas for the last generation of monarchs, these conditions are not likely to have a major impact on the population. The same can be said for northern Maine where the drought seems to be intensifying. Northern and western Michigan are abnormally dry but the reports from these areas indicate higher numbers of monarchs than last year at this time. Overall, the conditions appear to be excellent for the last generation of the season in the northern breeding areas.


3) 2003 Membership/Tagging Kits

Monarch tags are going fast! To make sure you receive all of the tags that you'll need for this fall's tagging season you should place your ASAP. Memberships include 25 tags, the pre-migration newsletter, the 2003 Season Summary (mailed summer 2004) and one or two additional mailings. Orders may be placed online via Gulliver's Gift Shop at

and offline orders may be called, faxed, or mailed to:
3515 Silverside Road, Suite 203
Wilmington, DE 19810
toll-free phone - (800) 780-9986
toll-free fax - (877) 687-4878

For your convenience, an abbreviated order form is available at


4) Peak Migration Dates - by Chip Taylor

When will the migration peak in my area?

We receive many questions from the public, reporters, and taggers as to when the migration is most likely to first arrive and to peak in their area. The following is a general, not a specific, guideline for when you are most likely to encounter good numbers of monarchs at each latitude. The table below gives the latitude, the midpoint of the migration and the period of peak abundance. These predictions are derived from reports to our list serve Dplex-L, communications directly to Monarch Watch, my personal observations and the thousands of tagged butterflies that have been recovered over the years. Each recovered butterfly is associated with a date and the dates of these recoveries show the migration to be relatively predictable over the continent. The record at specific locations for a given year may differ from this overall pattern but it has proven to be remarkably consistent when viewed as a large-scale phenomenon. As such, it has a phenology and it's predictable. Notice that I have used midpoint as a predicted date rather than a mean. We don't have enough information on the flow of the migration to generate a mean. Further, the distribution of the migrants appears not to be a normal bell-shaped curve but a curve that is shifted strongly to the left. Hence, when estimating the time of peak abundance below I have used a 12-day interval with 7 days before the midpoint and 4 days after the midpoint.

As mentioned above, this is a general pattern. It is likely to be modified by weather patterns that retard, such as strong southwesterly winds, or advance the migration, such as a series of rapidly moving cold fronts arriving from the northwest. Similarly, the pattern of the migration is likely to be modified along the coasts due to strong head winds or storms that have the effect of sweeping monarchs toward the coast on the backside of fronts.

Here's a challenge. If you are outdoors during much of the migration, why not keep a notebook and record the number of monarchs you see each day to see who well these general predictions fit your area this year? If you don't know your latitude, you can look it up quickly by typing your location into "How Far Is it?"

Midpoints and peaks of the migration by latitude.

Latitude / Midpoint / Peak in monarch abundance
49 degrees / 26 August / 18-30 August
47 degrees / 1 September / 24 August -5 September
45 degrees / 6 September / 29 August - 10 September
43 degrees / 11 September / 3 - 15 September
41 degrees / 16 September / 8 - 20 September
39 degrees / 22 September / 14-26 September
37 degrees / 27 September / 19 September - 1 October
35 degrees / 2 October / 24 September - 6 October
33 degrees / 7 October / 29 September - 11 October
31 degrees / 12 October / 4-16 October
29 degrees / 18 October / 10-22 October
27 degrees / 23 October / 15-27 October
25 degrees / 28 October / 20 October - 1 November
23 degrees / 4 November / 27 October -8 November
21 degrees / 11 November / 3-15 November
19.4 degrees * / 18 November / 10-22 November

*This latitude represents the general vicinity of the overwintering colonies. The monarch colony at El Rosario is usually opened to the public around the 18th of November.


5) Upcoming Monarch Events

Please send us information on tagging events, butterfly festivals and other events associated with monarchs that are open to the public. The following are public events we are aware of to date. Additional information will be sent in next month's update and posted online when available.

22-24 August - Powell Gardens Festival of Butterflies - Kingsville, MO - 9am-6pm daily Monarch Watch will provide hands on programs - Festival admission applies: $7 adults; $6 seniors; $2.50 children ages 5-12. More info:

6 September - Monarch Watch Open House, Lawrence, KS - You are cordially invited to join us on Saturday, September 6th 10am-3pm as we show off our new facilities on West Campus. We will provide the refreshments, lots of show & tell, tagging demos, and of course the monarch butterflies! we are now located in Foley Hall (2021 Constant Avenue) near the greenhouse. We hope to see you there! If you can't make it to Lawrence, we'll have something for you to check out online - for more information and a map visit

12-14 September - Butterfly and Nature Weekend, Portersville, PA - Tom Pawlesh will present this weekend program (open to the public) that will begin with a slide show on the life of the monarch butterfly, continue with tagging monarchs and finish with field work. For more info, contact North County Trail Field Office at or visit

13 September - Monarch Tagging Event - Baker Wetlands, Lawrence, KS - 7-11am - Annual monarch tagging event with Jayhawk Audubon Club.

13 September - MONARCH DAY XIX Blendon Woods Metro Park, Columbus, OH - 10 a.m. - 5 p.m. Celebrate the 2000-mile journey of these minute migrants during a day chock-full of activities. Live butterflies, displays, slide shows, video, and activities abound. Bring your camera and take your photo as a caterpillar! For more info, call 614/895-6221 or email

13 September – Monarch Tagging, Cedar Rapids, IA - 2:30-4:00 p.m. at The Indian Creek Nature Center, 6665 Otis Road S.E., Cedar Rapids, Iowa, 52403. Cost (members): $4.00 per person, and $10.00 for a family; Cost (non-members): $5.00 per person, and $12.00 for a family. Registration required by September 10, 2003. Contact the Indian Creek Nature Center at 319-362-0664 or on the web at

15-20 September - The Great Frederick Fair - Frederick, MD - Jim and Teresa Gallion, noted National Wildlife Federation Habitat Steward volunteers and Frederick County Master Gardeners will once again host a butterfly house at The Great Frederick Fair. Tagging and release of monarchs will take place during the week at 2pm and 4pm each day weather permitting. For more info visit

19 September Early PM - Monarch Watch in Central Park - Central Park (The castle), New York, NY - Monarch conservation and tagging activities.

20 September - Tagging at Monarch Watch, Lawrence, KS - KU West Campus, Foley Hall

27 September - Tagging at Monarch Watch, Lawrence, KS - KU West Campus, Foley Hall

27 September – Monarch tagging at Powell Gardens, Kingsville, MO - More info:

18 October TBA - Grapevine Butterfly Festival - Grapevine, TX - Butterfly festival & monarch tagging


6) Tachinid Update - by Chip Taylor

As reported in the last update, as a side project, I am rearing each of the third through fifth instar monarch larvae I find in the field this season to determine the number of tachinid fly parasitoids that occur in this area. This record should establish whether or not the incidence of parasitism, and the diversity of parasitoids, increases through the season.

Caterpillars have been more difficult to locate in July than they were in June. In June I found many larvae during the first hour of light, especially when morning temperatures in the 60s followed evenings in the 70s or 80s. Most of the overnight lows in July were in the 70s but, more importantly, the quality of the hosts shifted. In July most of the A. viridis, A. viridiflora and A. sullivantii were either senescing or developing seed pods. These mature plants may have been less attractive to monarchs than they were a month earlier. A. syriaca, the common milkweed, seemed to be the only milkweed of interest to the monarchs. However, this species is not common on my property and thus, on my morning walks, I surveyed relatively fewer plants usable to monarchs in July than I did in June. Tender shoots of A. verticillata and Cynanchum laeve (blue vine), are abundant but I have not found larvae on these species so far this year. Generally, monarchs use A. tuberosa as a host when it is in flower but the flowering has come and gone for this species this year and I found no evidence any of the plants on my property were used by monarchs.

The following is the record for June and July - Rate of parasitism of 3-5th instar larvae collected in the wild:

June ’03
Parasitized: 3***
Normal: 10
Deformed: 1
Dead/other causes*: 7
Proportion Parasitized**: .214

July ’03
Parasitized: 3***
Normal: 14
Deformed: 0
Dead/other causes*: 1
Proportion Parasitized**: .176

Parasitized: 6
Normal: 24
Deformed: 1
Dead/other causes*: 8
Proportion Parasitized**: .194

* Disease or pesticide – symptoms of non-inclusion virus, pesticide poisoning and unknown.
** Proportion of all J (pre-pupation) or pupal stage immatures from which tachnid larvae emerged.
*** A total of 5 fly puparia recovered from three monarch larvae
**** A total of 22 fly puparia recovered from 3 larvae.

Notes: 23 July – two mid 5th instar larvae turned yellow and brown in color and died but no fly larvae emerged. Upon dissection, 6 fly larvae emerged from one monarch larva and 4 from the other. I placed these larvae in a jar with the dead caterpillars and the larvae rapidly moved back into the monarch larvae perhaps to continue feeding. Subsequently, 15 puparia formed from larvae that exited these two caterpillars.

Three of the fly larvae were noticeably larger and the subsequent puparia were more elongate and showed striations not seen in the others.

25 July - 7 fly larvae emerged from one caterpillar. Two fly larvae photographed exiting a monarch caterpillar. Each laid down two strands of what appeared to be mucus behind them as they moved away from the caterpillar. This "mucus" quickly dried into coarse strands. When formed on a flat surface these strands became flat bands or strips of mucus that could easily be lifted with forceps.

Last month we posted images of the most common tachinid fly (Lespesia archippivora) that parasitizes monarch caterpillars.

However, various authors have recorded other tachinids and several other species of parasitoids that use monarchs as hosts. We are interested in obtaining records and specimens all of these parasitoids. Therefore, if you rear monarchs found in the wild and encounter parasitoids, we would appreciate receiving specimens. We would be glad to receive the puparia or the adult flies or wasps. They can be shipped in small vials or medicine bottles with tissue (not cotton). To make use of the specimens, we need the following information: Your name and address and the date and location where the monarch larvae were collected. Notes and observations about the parasites would also be appreciated. One goal is to make a photo archive of all monarch parasitoids but another is to get a broader picture of the distribution, diversity, and abundance of parasitoids in various areas of the country.

A few corrections have been made to the version of last month's update posted to the web site. I stated that the long strings by which the tachinid larvae slid down as they exit the J larva or pupa were "silk or tissue". I'm not sure what these strings are but they are not silk. If I were to make a guess, I’d say they were mucus. While photographing a monarch larva that had been killed by the tachinids, two fly larvae emerged. I photographed the fly larvae and the trails they left as they exited they monarch caterpillar. In the photos shown at

the exiting fly larvae produced "slime" trails of two or three inches that quickly hardened into bands along the side of a caterpillar and on the adjoining paper. It was not clear whether the material was secreted or excreted from the fly larvae or if the material was simply a coating that oozed off the larva once it left the body of the monarch. Last month I also described tachinids as slower than house flies but this really only applies to when they are searching for larvae. Otherwise, these flies are really fast. I also stated that the antennae were larger than those of house flies but this is not true. Yet, the antennae are more often projected forward in the tachinids making them more conspicuous to my eyes and my camera lens.


7) Imaginal Discs - by Chip Taylor

I have a long list of potential topics for these updates but I'm not making much progress eliminating items from the list since something new comes up almost every month. Recently I received an email from Pam Kahler (Wisconsin) that contained the following observation:

"I rear Monarch caterpillars during the summer because, if I don't, I notice that most eggs and larvae disappear. I just had a caterpillar with only one front filament. It pupated normally, but the chrysalis did have a discolored patch where a wing would be. I had always wondered if the filaments have any relation to the wings. The butterfly emerged yesterday and was missing one front wing. Do you know if there is a general understanding of the relation between the filaments and wings? To me they have always seemed to have a correspondence, but I have never read anything suggesting any such relation."

First of all - what is a filament? Monarch larvae have two pairs of filaments, sometimes known as feelers, which project dorsally from the back of the caterpillar. The first pair of filaments is located on the second thoracic segment (i.e., the segment that bears the second pair of legs)

and the second set is on the dorsum of the 8th abdominal segment. The second thoracic segment bears the first pair of wings in insects so it is logical for Pam to ask if there is a relationship between the development of the filament and the wing in the same location. These structures should not be referred to as antennae.

My answer was that I didn't know. However, it seemed certain to me that it was a developmental issue rather than one in which the filament had been damaged during the rearing. If monarch caterpillars are crowded, many of the filaments become damaged but the adult butterflies still emerge with normal wings. I suspect that the damage occurs most frequently just after caterpillars have molted to the next instar. For an hour or so, until the cuticle hardens, the newly molted larva is sluggish and vulnerable to the nibbles of hungry caterpillars. The damaged filaments "scar over" and the larvae continue normal development sometimes with no filaments at all. Thus, the filament does not appear to be tissue that is important for the development of the wings. But, could tissues that are destined to become wings have an impact on the development of the filaments? I'm not sure but maybe. To answer this question would require some experimentation, e.g., transplantations, and a detailed knowledge of the location, organization, and expression of the cells that compose the imaginal disc in the larva that becomes the adult wing. An imaginal disc is a group of cells in the larva that is programmed to become a specific adult structure. To explain these discs is to explain the process of the development of precursors to adult structures in the larva and the completion of this development within the pupal stage. Books have been written on this subject. I'll give you the short version here. Much of what is known about this topic is based on the fruit fly, Drosophila, and there is every reason to believe that, in general, the Drosophila model applies to Lepidoptera and monarchs.

As the monarch egg develops, at an early stage, cell populations arise that will eventually become adult epidermal structures such as legs, wings, eyes, and antennae. These groups of cells invaginate to form sack-like structures that are known as imaginal discs. The term imaginal is used because the cell clusters become adult tissues and another term for an adult is "imago". In Drosophila these discs increase 1000 fold during the development of the larva. Thus, clusters of cells destined to differentiate into adult structures during metamorphosis are initiated in the egg and well represented in the larva. It is during the pupal stage that these progenitors of adult structures undergo the final steps of differentiation and development that produces an adult butterfly with structures not seen in the larval stage.

Early research in this field involved transplants of imaginal discs or selective destruction of portions of a disc to determine the cells that produced adult structures. These studies have shown that imaginal discs are composed of groups of cells that follow specific guidelines. These discs are being "mapped" in terms of their compartmentalization and developmental priorities. In other words, researchers are defining how these clusters of cells are directed to become specific adult tissues.

So, getting back to the monarch with the missing wing, what happened? It seems probable that the imaginal disc that normally gives rise to the right wing was missing in the caterpillar and that the absence of the disc somehow affected the development of the filament on the caterpillar. An inspection of the thorax shows that the wing is entirely missing. It just didn't develop. All the other portions (sclerites) of the thorax on the right side are present and the right mesothoracic (middle) leg is normal.

Why is the imaginal disc missing? I don't know. There could be many explanations but this does suggest some experiments doesn't it?


8) Rearing Containers - by Chip Taylor

Monarch larvae can be reared in many different kinds of containers. Rosalyn Johnson sent us an email with the following suggestion:

"I cut the rounded bottoms off of one gallon transparent plastic juice jugs (e.g., for cranberry and grape juice) with a utility knife and place the jugs on several sheets of newspaper on a hard surface in the kitchen. Rather than replacing the plastic top, I cover the opening with a piece of plastic screening held in place with a rubber band. I hang a rinsed stem of milkweed with 6-7 leaves upside down inside the container. The cut end of the stem is covered with wet paper towel and protected with a bit of plastic wrap. The same twisty tie used to secure the wet paper and plastic can be hooked over the top of the jug to hold the milkweed in place above the paper.

This setup will keep 6-8 3rd or 4th instar larvae eating for about 24 hours. When they reach the 5th instar they eat the milkweed supply so quickly that I typically abandon the wet towel/plastic arrangement. When it's time to change the food supply, I wrap up the frass and leftover stems in the top sheet of newspaper for composting. The jugs are easily sterilized with bleach."


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