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Nov.,1911 RELATION OF BIRDS TO AN INSECT OUTBREAK 197 ing a careful investigation, found that a large proportion of the common birds fed upon the pests. The remarkable plague of caterpillars followed by a pest of butterflies that has existed the past spring and summer (1911) in the northern counties of California, especially in Siskiyou County, has furnished an interesting example of an insect outbreak. The economic importance of the outbreak may not have been as great as in the case of some others, but the numbers of individuals and the extent of the plague mark it as one of the most notable in the history of the state. Reports as to the great numbers of the worms are meagre, but the defoliated .. '.? " brush throughout Siskiyou County, where the plague was most severe, bears mute testi- mony to their work. When great swarms of butterflies made their appearance, the aspect of the outbreak became so extraordinary that the news- papers published numerous, often exaggerated accounts, of the phenomenon. From all accounts,the vicin- ity of Mount Shasta was most affected, both the worm and the butterfly being abundant at Weed, Igerna, and Sisson, three towns on the western base of the mountain. The worms were reported as being very abundant at Marble Mountain in western Siskiyou County and at Weaverville, Trinity County. Although no butterflies in any numbers were noticed at Redding, Shas- ta County, they were reported Fig. 68. THE LIFE HISTORY OF' Eltgonia californica. THE as very abundant in the moun- EGGS SHOWN ARE NoT THOSE OF E!lgonia californica BUT tains thirty-five miles east of THOSE OF A MOTH OF A TENT CATERPILLAR WHICH ALSO LIVES ON SNOW BRUSH. THE EGGS OF E!tgonict ARE SIMI- that place. LAR TO THESE AND ARE CLUSTERED ON A SMALL BRANCH The following abstract is IN MUCH THE SAME MANNER. NOTE THE STIFF HAIRS ON made from a letter by Hon- THE LARVA; THE SHAPE AND GENERAL CHARACTER OF orable J. B. Curtin, dated THE PUPA, AND THE SIZE AND APPEARANCE OF THE ADULT September 11, describing a similar outbreak, of far less extent, in the Sierras. "Aspen Valley is a part of my cattle range and is at an elevation of six thousand three hundred and fifty feet. For a distance of about a mile each way, that would be east and west, the caterpillars have been traveling, going north. As far as I can learn, they are now in the central part of the county (Tuolumne) and have traveled perhaps thirty miles north from the south fork of the Tuolumne River. They fed only on snow brush, stripping each bush of its leaves."