Activity #1: Summary of Monarch Density Data

All participants must complete the "Summary of Monarch Density Data."

Download the datasheets and directions (PDF)

Objective: Obtain a count of monarch eggs and larval instars at the site by examining a known number of milkweed plants. The result will be a per plant density measurement of the monarch population at the site. We can use this measurement to see how monarch densities vary within a year, between years, and among different sites and locations.

Method: Examine as many milkweed plants as possible, keeping track of the number of plants examined. Record the number of eggs and monarch larvae of each instar that you find. Try to monitor on the same day and at the same time each week, if possible, throughout the time that milkweed is growing in your area. It is critical that you record the number of milkweed plants that you examine. The result will be a weekly estimate of monarch density at your site, measured as a proportion of milkweed plants with monarchs. It is also important to examine an unbiased sample of milkweed plants. In other words, you should not just look at the milkweed plants that you think are most likely to have monarchs on them because you will overestimate the monarch density at your site. You can avoid bias by following the directions below.

1. Walk one or more straight-line transects, or path, through your site. Hold your arms out to your sides as you walk. Stop and examine every milkweed plant that falls along your path between your fingertips. As you examine these plants, keep track of the number of plants you look at, whether they have monarchs or not. Record the total number of plants you examine on Date Sheet #1 (which has rows for several days) or data sheet #1A (which only has rows for one date – it is useful to use 1A if you are also doing activity 4).

Note: you do not need to use the transect method if you are able to examine all of the milkweed plants at your site.

2. Search for monarch eggs and larvae on each plant. To examine a milkweed plant, remember that monarch eggs and larvae can be hard to find! Look carefully at all parts of the plant, including the bottoms of the leaves and the area within the very small leaves at the top of the plant. Keep an eye out for caterpillar clues, such as chew marks on the leaves. Try not to handle the plants roughly, to avoid knocking any larvae off the plant. Remember, not all eggs and caterpillars that you find on milkweed are monarchs; use the pictures of each instar below and A Field Guide to Monarch Caterpillars to help you distinguish monarchs from other insects.

3. Keep track of the number of monarch eggs and larvae that you find, and the instar of each monarch larva. Record the totals on Data Sheet #1 or 1A. Note that there is also a space to record the number and stage of any dead monarch eggs or larvae that you find.

4. Scan for adult monarchs. Note any adult monarchs you observe, and their gender, if known. To avoid counting individuals more than once, count the maximum number of adults that you observe at any one time. Record this number on Data Sheet #1 or 1A, indicating how many are males, females, and unknown.

5. Note what plants are blooming each week. This information will help us know something about the diversity of plants at your site and tell us if there were any nectaring plants there to attract adult monarchs. You do not need to record the numbers of each kind of plant that is blooming, just the species.

6. Note any disturbances at the site. Record the date and type of disturbance on the bottom of Data Sheet #1. Disturbance might include mowing, herbicide spraying, haying, or other activities that would temporarily or permanently damage the milkweed plants.

7. Record the rest of the required data on Data Sheet #1. Record the date you monitored, the temperature (indicate Fahrenheit or Celsius), start and stop times, etc.

Male and female monarchs can be distinguished easily. Males have a black spot (indicated by a red arrow) on a vein on each hind wing that is not present on the female. The ends of the abdomens are also shaped differently in males and females, and females often look darker than males and have wider veins on their wings.

Images, from left to right: Monarch egg on milkweed leaf—The egg is a little more than 1 millimeter tall. Close-up of monarch egg—Note the pointed shaped, the glossy color, and the vertical striping. Monarch first instar consuming eggshell—Note the dull greenish-grey color, and the size (not much bigger than the egg). First instar feeding damage—This circular feeding pattern is an indication that a monarch first instar was on the plant at some point. Monarch fourth instar—Older monarch larvae have bright yellow, black and white striping and 2 pairs of tentacles (on front and back ends).

Male and female monarchs can be distinguished easily. Males have a black spot (indicated by red arrow) on a vein on each hind wing that is not present on the female. The ends of the abdomens are also shaped differently in males and females, and females often look darker than males and have wider veins on their wings.

 

You may use Data Sheet # 1A in the field for weekly data collection.

The information collected on this field data sheet (1A) can be transferred to Data Sheet # 1: Summary of Monarch Density Data at the end of each week's monitoring.

Download Datasheet 1A (PDF)