University of Minnesota

Frequently Asked Questions

Milkweed Community
Monarch Biology


I would like to volunteer to monitor monarch populations in my area. How can I be trained to monitor my own site?

The training methods are described on our website. You could teach yourself by using the directions on the website, or attend a training session given by someone who attended a train-the-trainer session in your area. The dates of these sessions are found in the Training section on our website. You can also watch our online training videos if you are unable to get into an in-person training. If you have any questions, feel free to contact us:

We are a nature center outside the state of Minnesota and would like to host a training session for several nature centers in our area. How do we go about doing this, and what are our responsibilities?

Contact us to see if a training session in your region fits into our long-term plans. If it does, we ask that the cooperating nature center take care of all the recruiting and planning, and schedule meals and lodging for the naturalists that attend. Our fees will vary depending on the number of our staff needed, the lenght of the workshop and if travel is required. Our base rate is $100/hr per staff needed, plus mileage or travel costs. 


When should I start and stop monitoring my site?

It's best to monitor every week as soon as the milkweed comes up. It is just as important to document monarch absence as it is to document presence. You will almost always see eggs before you see adults, so you shouldn't wait until you see your first adult to start monitoring. In the fall, you should monitor until all of the monarchs are gone. We recommend going out twice after you've seen your last egg or larva.

There have been no monarchs at our site so far this year. Do you still want my data even though it shows no monarchs?

Yes! We definitely are interested in your data. Even though it is discouraging to find nothing, understanding where there are no monarchs and when is just as important as learning where and when there are monarchs. This is important because we'll learn a lot about monarch distribution and population dynamics.

I recently came back from vacation and my site was mowed down. What should I do now that I no longer have milkweed?

You should note that it was mowed in the notes for that site, and then hopefully when the milkweed comes back it will have even younger plants that are more attractive to monarchs. Milkweed typically grows very quickly, so you might even start to see small growths of it coming up above the rest of the plants in your area fairly soon after mowing.If no milkweed comes back within a few weeks, you won't be able to monitor – at least until next year.

How will the data that I collect be used?

Once your data is entered into our database, you will be able to see graphs showing the numbers of monarchs that were found at your site each week that you monitor. Graphs for each year are also posted for all of the other sites that are a part of this project, along with annual graphs for the eastern population. The data you collect will help us answer basic ecological questions about the abundance and distribution of monarchs over time and geographical locations. A more comprehensive list of questions that the data can be used to answer appear in the monitoring section of the website.

Not only will scientists be able to publish scientific papers using the data you collect, but since the graphs are available to the public, many teachers and students can use them in their own classroom investigations!

You can see a list of and read papers that have been published using MLMP data here.

I have a question about activity #4, Comparing Plants Occupied by Monarchs to Random Plants. I found an additional 7 monarch eggs when I filled out the sheet on Characteristics of Random Milkweed Plants. Do I transfer this data over to the sheet Characteristics of Milkweed Plants with Monarchs sheet and double count them, or do I keep the counts separate?

The goal with these two activities is to compare a random sample of plants to plants with monarchs on them. Some of the random plants may have monarch eggs or larvae on them and you should just note the monarchs as invertebrates on the plants. You can also put data for theses plants onto the Characteristics of Milkweed Plants Occupied by Monarchs sheet. However, if you are going to count them in your density count for the week, you need to include the 30 plants that you checked as part of your sample size. You should only do this if your random sample of plants did not cross the transect you took to get monarch density. Thus, you aren't really double-counting them.

Can I collect daily temperature and rainfall data from my home or the National Weather Service if it is collected close to my site?

Collecting rainfall and temperature data from your site would be best since rainfall and temperature can be quite "patchy". However, if the weather service station is within a reasonable distance from your site, then using that data would be fine. You should make a note of this on your data sheet.

How many milkweeds do I need in order to establish a site?

In order to establish a MLMP site, milkweed must be present since monarchs only lay their eggs on milkweed.  At a minimum, we recommend that you select a site with at least 12 plants.  Of note, scientific studies estimate that it takes approximately 30 milkweed plants to produce one adult monarch due to predation, disease and other pressures on immature (eggs and larvae) monarchs.  Therefore, while sites with low milkweed numbers may still foster immature monarchs, sites with more milkweed are more likely to yield observational data.

Milkweed Community

I observed a mass of 50-100 caterpillars (not monarchs), about 1/3 inch long and white with black heads. The first stage of the larvae looks slightly furry and light brown. They are skeletonizing the milkweed, eating everything but the veins and ribs. Any idea what these might be?

These are milkweed tussock moth caterpillars. They are gregarious for the first week or so, and then will go their individual ways. They'll soon be furry with big tufts at each end of their body. The female lays an egg mass, and the larvae are synchronized in everything they do, including molting.

As I am monitoring I find a lot of eggs, but I don't see many larvae. What would most likely be eating the eggs or first instar larvae?

There are lots of things that eat monarchs! Ants, spiders, red velvet spider mites and stink bugs are some we see frequently. Some monarch larvae also die when their mandibles get gummed up by the milkweed latex.

I read that while there are 106 types of milkweed, monarchs only lay their eggs on certain kinds and that they avoid others because of the level of toxicity. I'm worried because the only type of milkweed we have so far is the butterfly weed (asclepias tuberosa) and it has no milky substance in the plant. What milkweeds do monarchs like?

There are actually very few species of milkweed that monarchs won't eat. Among the ones they will eat, they certainly have preferences. We know that female monarchs will lay their eggs on Asclepias tuberosa, and monarch larvae will eat it. However, we find in the lab that A. tuberosa is not one of their favorite milkweeds to eat. If you monitor a patch of A. tuberosa, you will likely find some eggs and larvae on it, but you may not find as many per plant as you would find on some other species (e.g. common milkweed [A. Syriaca] or swamp milkweed [A. incarnata]).

Monarch Biology

How do you tell which "instar" a larva is in?

If you look on our website in the Biology & Research section, there's a section called Monarch Life Cycle. This shows you comparisons of the head and tentacle sizes for the different instars. Life cycle card sets and the Field Guide to Monarch Caterpillars, available in the  Monarch Store, also give great descriptions of each stage.

Is it unusual to find more than one monarch egg on a milkweed plant?

It's not too unusual to find more than one monarch on a milkweed plant. Although an individual female usually lays only one egg per plant, multiple females may use the same milkweed plant.

Do the same monarchs that migrate to Mexico each fall return to my area each spring? How long does a monarch live, and how far can they fly in a day?

If you live in the northern part of the country, the same monarchs that leave in the fall, on their way to Mexico, don't return to your area in the spring. Monarchs that migrate to Mexico live about 8-9 months as adults (from late summer or fall until the following spring). When these monarchs return to the southern US in March, they lay eggs there and die. The offspring of the migrating monarchs are the ones you see in the mid-section and northern part of the country in the spring. Monarchs that you see in your area during the summer breeding season live about 4-6 weeks. The ones that migrate live longer because a) they don't reproduce until spring and reproduction uses up a lot of energy and other resources, and b) they are in a semi-dormant state while they are overwintering in Mexico. They can fly about 50 miles a day while they're migrating.

Are there parasitoids that use monarch larvae as hosts?

Both fly and wasp parasitoids use monarch larvae as hosts, but the most important larval parasitoid is probably a fly species in the family Tachinidae. This family includes about 10,000 species, most of which parasitize Lepidoptera (butterflies and moths), although they also parasitize Hymenoptera (ants and bees), Heteroptera (true bugs and their relatives), Coleoptera (beetles), Diptera (flies and mosquitoes), Dermaptera (earwigs), Orthoptera (grasshoppers and crickets), Chilopoda (centipedes), as well as some scorpions and spiders. Research in the Monarch Lab suggests that species Lespesia archippivora (La) is the most important monarch tachinid parasitoid. It is widespread throughout North and Central America, has been found in Brazil, and was purposely introduced into Hawaii for biocontrol in 1898.

How do tachinid flies develop within monarch larvae?

Female La lay eggs on the host integument (skin), and the fly larvae hatch and bore into the host soon after oviposition. La complete their larval development within the host, the maggots emerge from late larvae or pupae, and then pupate in leaf litter and eclose within about 10-14 days. Fly maggots drop to the ground on long, gelatinous tendrils that look like white strings hanging from the monarch.

How do wasp parasitoids use monarchs as hosts?

Less is known about the extent to which other parasitoids attach monarchs, but at least one wasp in the family Braconidae has been reported in monarchs (Arnaud 1978). The closely-related queen, Danaus gilippus is parasitized by two Chalcid wasps as well as L. archippivora (Arnaud 1978). Current research in the Monarch Lab demonstrates that the wasp Pteromalus puparum (in the family Pteromalidae and the same superfamily, Chalcidoidea, as the two Chalcid wasps found in queens) could be an important pupal parasitoid (Oberhauser et al. in preparation). Pteromalus puparum wasps are tiny, and over 200 can emerge from one monarch pupa.

  • © 2016 Regents of the University of Minnesota. All rights reserved.
  • The University of Minnesota is an equal opportunity educator and employer. Privacy