University of Minnesota

Section 3c: MLMP Activities - Measuring Monarch Density

This is video seven of the Monarch Larva Monitoring Project video training series, providing instruction on how to accurately measure monarch density and how to use MLMP data sheets. The data collected are used to examine how monarch density varies over time and among different sites and locations.

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Related Activities

Photo Credits (in order of appearance)

  1. Asclepias syrica, or common milkweed patch: Wendy Caldwell
  2. Asclepias syriaca in bloom: Monarch Watch
  3. Caterpillar signs on milkweed: Deb Marcinski
  4. Monitoring site with mowed trail: Peg Baseden
  5. Aphids on milkweed leaves: Grant Bowers

Glossary Terms (in alphabetical order)


protection and preservation through careful management.


singular, datum: factual information that can be used as a basis for understanding something.


a system of interactions between a community of living organisms and their environment.


the waste product of larvae, called caterpillar poop by most. Monarch larvae produce a lot of this, especially in their later instars.

Oe (Ophryocystis elektroscirrha)

a protozoan that infects monarchs and is known to decrease health, fecundity, and life span. It is passed by infected females to offspring when protozoan spores are rubbed onto milkweed (eaten by developing caterpillars) as they are laying their eggs.


insects that lay their eggs on or inside another insect species (called their host). The eggs hatch and feed on the host from the inside, eventually killing the host.

sample size

the number of replicates in an experiment. Larger sample sizes reduce the effects of random chance.

tachinid flies

(tah-KIN-id): a fly family with about 1300 species in North America. Parasitic tachinids usually attach eggs to the outside of the host’s body. The eggs hatch, then the tachinid larvae burrow into the host and begin feeding inside. The host is almost always killed. The species that live in monarchs are gray and smaller than houseflies.


a sample strip of land used to monitor plant or animal populations and distribution within a given area.

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