Some volunteers find it easiest to rear monarch caterpillars until they become adult butterflies to sample for parasites. Here are some tips for rearing caterpillars to adult butterflies:

Rearing caterpillars to adult butterflies:

Step 1: Collect 4th or 5th instar larvae (greater than 1.5cm in length) from wild milkweed plants using a pint-sized plastic container. Here's what the 1st-5th instars of monarch larvae look like:

1st-5th instars of monarch larvae.

A 4th instar larvae munching on milkweed leaf.

Step 2: Set up containers for larvae.

Wear gloves to prevent contamination. Set up plastic containers with damp paper towel—moist to touch but no standing water.  Add a sprig of freshly rinsed milkweed, then add the larva in and close the lid.  Label container with collection date, collection site, and the estimated size of caterpillar at time of collection. 

Put only one caterpillar in each container.

Step 3: Monitor caterpillars.

Each day, empty frass (caterpillar feces) from bottom of container, replace paper towel if soiled, and add a fresh milkweed stalk.

Caterpillars usually spin silk pad on the lid within 5-6 days and hang from this.  After the green chrysalis forms, discard the plant material and wait for butterfly to emerge (10-12 days).

Step 5: Sample the adult butterfly for parasites.

Between 4-12 hours after emergence, sample the butterfly for parasites using the testing procedures.

Step 6: Sterilize the containers and rearing area.

Thoroughly sterilize container with 20% bleach solution and clean all supplies and tools with bleach wipes before rearing another wild monarch. THIS IS VERY IMPORTANT!!! If the caterpillar was infected and the area was not properly cleaned, you could potentially infect a healthy caterpillar using infected containers.