REVISION MALACOSOMA HUBNER IN NORTH AMERICA 145 



the situation is not well known since c. ambisimile was not collected north 

 of Big Basin Redwoods State Park in 1 960, and c. calif ornicum was not 

 found west of the ridgeline at all. One vial, however, of twelve larvae in 

 the collection of the California Department of Agriculture that was 

 collected on Ceanothus thyrsiflorus in Tunitas Canyon, 6 niiles south oi 

 Half Moon Bay, San Mateo County, contains larvae which must be 

 regarded as coming from an intermediate population since characters 

 of both c. ambisimile and c. calijornicum are present in varying combina- 

 tions. More extensive collections on the west side should reveal a 

 situation similar to that found on the east side (see comments). East of 

 the Bay its northern distributional limit seems to be the San Jose area 

 since 10 larvae from Silver Creek Hills (SE. edge of San Jose) are 

 typical c. ambisimile, A single specimen from Alum Rock Park just 

 east of San Jose is a typical c. calijornicum. The southern limits of its 

 distribution are not definitely known, but it was taken 8 miles south of 

 HoUister in San Benito County during this study, and one adult speci- 

 men from Carmel in Monterey County has been seen. There seems to 

 be no reason why it should not occur farther south since fruit trees have 

 been introduced into much of the area south of Monterey Bay, but it 

 may be adapted to the more humid climate north of there. 



COMMENTS. — The area near Los Altos where c. ambisimile inter- 

 grades with c. calijornicum was studied more intensively than other areas 

 in order to obtain a better understanding of the relationships between 

 the two populations. Figure 6 shows the collections in which only 

 typical c. calijornicum or c. ambisimile were found, and the collections 

 in which a mixture of various intergrading forms of larvae were found. 

 Larval collections made by other persons are included in the map, but, 

 even so, the number of collections is small, despite the fact that nearly 

 all of the roads between Saratoga and Menlo Park were traveled in 

 searching for colonies. In the area around Los Altos where colonies 

 were abundant, every conceivable kind of intermediate color pattern 

 was found, ranging from the extremes of bluish-sided larvae with orange 

 lateral setae (fig. 356) to the opposite extreme of black larvae with 

 white lateral setae (fig. 357) {c. calijornicum normally is black with 

 orange setae and c. ambisimile is bluish laterally with white setae). 

 Practically no colonies were found in this area which were 100 percent 

 one subspecies or the other, indicating that the variation was real, and 

 not due to larvae of different colonies becoming mixed after hatching. 



In one case a single tent was collected on apricot >2 mile southwest of 

 Los Altos (Coll. No. 20). The caterpillars were in the process of molting 

 from the second to the third instar, indicating that all had developed 

 at about the same rate and had probably hatched from the same 

 egg mass. No other tents were found on the same tree or on any other 



