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 
as very abundant in the moun- 
tains thirty-five miles east of 
that place. 
The following abstract is 
made from a letter by Hon- 
orable J. B. Curtin, dated 
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.” 
Fig. 6.S. THB ijFK HISTORY OK Eiigonia caHfor/iica. the 
EGGS SHOWN ARE NOT THOSE OF liugotiia califor)nca BUT 
THOSE OF A moth OF A TENT CATERPIELAR WHICH ALSO 
LIVES ON SNOW BRUSH. THE EGGS OF Eltgonia ARE SIMI- 
LAR TO THESE AND ARE CLUSTERED ON .A SMALL BRANCH 
IN MUCH THE SAME MANNER. NOTE THE STIFF HAIRS ON 
THE larva; the shape and general ch.aracter of 
THE PUP.A, AND THE SIZE AND APPEARANCE OF THE ADULT 
