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Monarch Health Annual Results


Every year, we compile all of the data from our community scientists and analyze it to determine what trends are emerging. Starting in 2011, we began our annual newsletter, which we send out to all participating volunteers. These newsletters highlight the trends from the year, as well as provide an update on the Monarch Health team. Click on the year below to see a recap of the results, plus a link to that year's newsletter.

2021-22 Results

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It is with great excitement and pride that we share with you our 2021-22 newsletter! We've included a summary of our last two years of volunteer-collected data, reviews of some late-breaking monarch research, and more.

2020 Results


In 2020, community scientists collected 6417 samples for Project Monarch Health. The average number of samples per volunteer was 38.66. Infection prevalence by the protozoan OE was 24.8% across all samples, with highest infection prevalence occurring in the southern US, in regions with resident, non-migratory monarch populations. 

2019 Results

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In 2019, community scientists collected 9525 samples for Project Monarch Health with a record number of states and provinces sampled!. The average number of samples per volunteer was 53. Infection prevalence by the protozoan OE was 20% across all samples, with highest infection prevalence occurring in the southern US, in regions with resident, non-migratory monarch populations. 

2018 Results

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In 2018, community scientists collected a record number of samples for Project Monarch Health, and monarchs numbers reached at 12-year high in Mexico! 207 volunteers from 32 US states and 2 Canadian provinces submitted 10,497 samples to Project Monarch Health. The average number of samples per volunteer was 50.71. Infection prevalence by the protozoan OE was 24.6% across all samples, with highest infection prevalence occurring in the southern US, in regions with resident, non-migratory monarch populations. Just under 60% of these samples were heavily infected, down from the previous year. The prevalence in eastern migratory populations was up from last year at around 20%.

2017 Results


In 2017, 225 volunteers tested 7,356 monarch butterflies for the protozoan parasite Ophryocystis elektroscirrha (OE). Our citizen scientists sampled across 29 states in the US and 2 provinces in Canada. Both the southeastern US and California populations exhibited very high infection prevalences, both at 67%. In contrast, only 5% of the eastern migrants were heavily infected with OE.

2016 Results

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In 2016, 152 Monarch Health volunteers sampled 5,832 monarchs for OE. This season we saw a rise in OE prevalence in all migratory regions except the Midwest. Notably, the West rose from 20% in 2015 to 37% in 2016 while the South and Northeast appear to be returning to the average prevalence of 10% previously maintained by these populations from 2005-2013. The non-migratory populations in South Florida, and along the Pacific and Gulf Coasts are still maintaining high OE infection levels, however the Pacific did drop significantly from 68% in 2015 to 43% in 2016.


Overall, we see higher OE prevalence in these monarchs because they are not migrating. This means that they cannot escape infected milkweed and sick individuals are not weeded out by the strenuous long-distance migration. Disease builds up in these populations, particularly when tropical milkweed (A. curassavica) is present to facilitate year-round breeding.

  • Where can I find caterpillars to rear or adult butterflies to sample?
    The best places to find caterpillars in the wild are areas with milkweed plants. Successfully finding caterpillars and adult butterflies will depend on where you live and the time of year. In many areas, butterflies are not often found in the summer months. Sightings can be more common in the spring and fall periods during migrations. Be persistent! If you have kits and are not seeing butterflies, don't give up – migrations may be just around the corner! The easiest places to find caterpillars and adult butterflies are state parks, gardens, and other natural areas. Please always make sure when removing caterpillars or catching adult butterflies on private property or in botanical gardens to ask permission and/or notify the proper authorities.
  • What does a pupa with OE look like?
    Typical signs of OE infection in pupae include dark coloration that will initially show up on the abdomen and thorax areas, just underneath the cuticle (hard exterior of the pupa). These dark patches can be isolated as a few small spots, or may extend across all abdominal segments, thorax, and head. The signs of infection first appear about 3 days before adult butterflies emerge, before monarchs produce their own body pigment, and will progress each day. Often, these dark patches are distributed asymmetrically, whereas the monarch’s own pigment is symmetrical from the middle line of the abdomen. It is important to contrast the heavy dark coloration that OE infection presents in pupa versus the symmetric coloration that can be observed in non-infected pupa while normal pigmentation is happening. Sometimes a damaged or wounded pupa will present external wounds that could be dark black; however, it is important to remember that OE development occurs underneath the cuticle, and thus appears dark grey when viewed externally. Pictures: top=healthy pupa, middle=infected pupa, bottom=infected pupa with wound
  • Why are my caterpillars sick?
    Larvae can die from many causes besides OE, including infection with bacteria, viruses, parasitoids, and temperature extremes. • If you observe group deaths or individual caterpillars showing any of the following symptoms: vomiting, writhing, diarrhea, then it is likely they have been exposed to chemical poisoning. This can be a result of any pesticides used on the milkweed plants. • If caterpillars are not eating, lethargic, and turn brown or black, then bacterial or viral infections are possible. In any case where you observe caterpillar illness or death, immediately remove the affected individuals from the rearing containers, bleach the containers, and move remaining healthy individuals to new, clean containers with fresh plants.
  • Will sampling for parasites hurt a butterfly?
    No. Monarchs are very sturdy and it is difficult for scales to be removed. It is important to apply enough pressure with the sticker on the abdomen to get a sufficient amount for a sample. You should see black coloration on the sticker when placed on the notecard.
  • Where can I get milkweed plants?
    Finding milkweed in the wild can be difficult, but it's the easiest way to find whole plants. Otherwise, check your local nursery for native milkweed species for your area. To see which species are native to your area, click here and find your state. Unless you live in a tropical area, we discourage using Asclepias curassavica, tropical milkweed, which is not native to North America. You can also order milkweed seeds from online native plants suppliers such as Prairie Moon Nursery, Butterfly Encounters, or Easywildflowers.
  • What should I do if I've planted non-native tropical milkweed?
    Because tropical milkweed continues to grow and bloom throughout the winter, it can reduce the need for monarchs to migrate. This lack of migration can result in increased OE prevalence in these resident populations. We suggest cutting back your tropical milkweed in the fall to mimic the "dying back" of native plants during this time. Or, you could remove these plants and replace them with native milkweed species. You can buy them online from Prairie Moon Nursery.
  • Why do I need to wear gloves and try and maintain sterile conditions?
    The parasite spores are very small and easy to accidentally spread around. It's important to wear gloves to minimize the spread of spores from one sample to another. Always change gloves between handling different butterflies. One monarch may be infected, while another may not. It's important to try and keep a clean work area when handling and sampling the butterflies for parasites. Bleaching any containers, tools, and work surfaces the butterflies touched prevents cross-contamination of different samples and helps avoid touching a non-infected sample with infected spores from another. We suggest a 20% bleach solution be used between sampling individuals and also between different sampling periods.
  • What do I do with infected monarchs?
    Read about this here.
  • Should I mail an empty chrysalis or part of a deceased butterfly to be sampled?
    No. Unfortunately, we are only able to collect usable samples from the abdomens of monarchs so we cannot use other parts or the empty chrysalis to get an accurate estimate of the OE spores.
  • Should we send you tachinid fly pupa if they emerge from the chrysalis?
    No, but you can send them to the Monarch Larva Monitoring Project
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