462 



INJURIOUS AND BENEFICIAL INSECTS OP CALIFORNIA. 



eggs —usually upon one of the food 

 plants — from which the caterpillars 

 hatch in a short time. During 

 March and April they often be- 

 come very abundant. This was 

 particularly true in 1914. When 

 fully matured they hang up by the 

 tail and transform into chrysalids, 

 which mature, in from one to two 

 weeks, into butterflies. There are 

 apparently several broods a year, 

 the spring brood being usually the 

 largest. This species sometimes 

 migrates in great numbers, the 

 flights lasting a week or more, as 

 the migration in 1902. All fly in 

 one direction. 



Nature of Work. — The caterpil- 

 lars devour the leaves and smaller 

 stems of the food plants, often leav- 

 ing only the larger woody stalks. 



Distribution. — This butterfly is 

 very common throughout the south- 

 ern part of the State, but occa- 

 sionally appears in the central and 

 northern parts in somewhat limited 

 numbers. 



Food Plants. — Ordinarily the 

 caterpillars feed only upon wild 

 non-economic plants, as thistle, 

 malva, Amsinchia, nettle, marsh- 

 mallow, etc., but occasionally gar- 

 den plants, especially beans, are 

 attacked. 



Control. — The elimination of the 

 host plants around the fields of 

 cultivated crops will usually serve 

 to keep the latter free from attacks. 

 However, if infestation occurs poi- 

 son sprays may be employed, but 

 not on vegetables soon to be used 

 for food. Control measures are 

 seldom necessary for this butterfly. 



Natural Enemies. — An internal 

 hymenopterous parasite, Apantelcs 

 carduicola Pack. 320 has been re- 

 ported as preying upon this species. 



'"'•Insect Life, III, p. 16, 1890. 



Fig. 473. — The thistle butterfly, Vanessa 

 cardui (Linn.). Larvae, pupae and adults. 

 Natural size. (Original) 



