Every fall, nature enthusiasts in California rejoice as thousands of monarch butterflies, or Danaus plexippus, arrive to spend winter. These tiny creatures cover over 3,000 mi (4,800 km) flying from their breeding sites in the northern states to the south. Some of the largest monarch sanctuaries are located on the Central California Coast, however, San Diego is also among their favorite wintering destinations.
Monarchs arrive in California around mid-October and stay until early February. They can be spotted around San Diego parks and private gardens. The north end of the University of California San Diego campus, in particular the Eucalyptus Grove at the Ecological Park, is among the spots where butterflies are seen regularly. They flock to eucalyptus and other trees that are flowering in the winter to feed. When the temperature is cold (below 55 °F or 14 °C) butterflies usually stay on the trees forming clusters. Unfortunately, the monarch population coming to San Diego has decreased considerably over the recent years. Scientists point to the extensive use of pesticides and urbanization to account for this decline.