Monitoring milkweed patches for the Monarch butterfly

Monarch butterfly

The Monarch butterfly (Danaus plexippus) is vulnerable throughout its lifecycle. Its overwintering sites in Mexico (6-12 hectares of Oyamel forests in the transvolcanic mountains) are threatened by logging. The milkweed food plants it needs on its amazing migratory pathways across North America are considered to be noxious by many people and removed. In addition, though these are not well understood, agricultural pesticides may harm Monarch populations, and invertebrate predators and parasites on the larvae can decimate populations.

From 2004, A Rocha USA has been monitoring a milkweed patch weekly through the summer for eggs, larvae and adults within the bounds of Washington DC, in conjunction with the National Park Service. This is part of the "Monarch Larval Monitoring Project" – a nationwide citizen science project to increase understanding of the population biology of the Monarch and threats to its survival. A second important aim is to give people hands-on field experience, to enhance their understanding of Monarchs and their habitat and the scientific process in general.

A Rocha USA has trained 10 volunteers in the monitoring process. 2004 was a very bad summer and winter for Monarchs, and we found very few eggs and only early-stage larvae. However early results from sites across the USA and from our own observations suggest that 2005 is showing somewhat of a rebound in the Monarch population. Monarchs require nectar plants as well as milkweed, and we will be advising the National Park Service that the Washington site would be more "Monarch friendly" with the addition of a range of native nectar-providing plants.

Project leader: Ann Stuart. For further information contact usa@arocha.org

Partners: Monarch Larva Monitoring Project, National Park Service