Question 1

Where can I find caterpillars to rear or adult butterflies to sample?

Accepted Answer

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.

Question 2

What does a pupa with OE look like?

Accepted Answer

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

Question 3

Why are my caterpillars sick?

Accepted Answer

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.

Question 4

Will sampling for parasites hurt a butterfly?

Accepted Answer

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.

Question 5

Where can I get milkweed plants?

Accepted Answer

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.

Question 6

What should I do if I've planted non-native tropical milkweed?

Accepted Answer

While native milkweeds die back in the late fall and return in the spring, non-native milkweeds such as tropical milkweed (Asclepias curassavica) continues to grow and bloom all winter. This interferes with monarchs' annual migration, because increasing numbers of monarchs are opting to live year-round where non-native milkweeds can persist throughout the winter instead of completing their migration. Migration has historically served as a sort of "reset button" for OE infections, because very few sick monarchs are able to successfully migrate, resulting in a majority healthy population each spring. Now, this lack of migration is resulting in increased OE prevalence in resident (non-migratory) populations. For example, of all the samples we received in 2023 from Florida (where tropical milkweed is common year-round), 80% were infected.

If you have tropical milkweed in your yard, please consider at least cutting it down to the soil or bringing it indoors in the fall to mimic the "dying back" of native plants during this time. Even better, you could remove these plants and replace them with native milkweed species. You can buy them online from Prairie Moon Nursery. To find out which native milkweed species might thrive in your area, you can consult the Xerces Society's Regional Milkweed Guides.

Question 7

Why do I need to wear gloves and try and maintain sterile conditions?

Accepted Answer

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.

Question 8

What do I do with infected monarchs?

Accepted Answer

Read about this here.

Question 9

Should I mail an empty chrysalis or part of a deceased butterfly to be sampled?

Accepted Answer

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.

Question 10

Should we send you tachinid fly pupa if they emerge from the chrysalis?

Accepted Answer

No, but you can send them to the Monarch Larva Monitoring Project

Frequently Asked Questions