THE INSECT AS A PARENT 203 



a dark day in Washington" (writes Dr. Howard) " I once 

 saw a migrating army of cockroaches, incalculable in 

 number, crossing the street from a dirty restaurant toward 

 buildings opposite. The majority of the individuals com- 

 posing the army were females carrying egg-cases, and the 

 observation thus became one of psychological interest since 

 the migratory instinct seemed to have been developed by 

 an appreciation of the fact that while the restaurant might 

 support the mothers there would not be enough food for 

 the coming children." Another American observer (Mr. 

 H. G. Hubbard) has described the habits of certain bark- 

 frequenting Psocidce which feed upon lichens. The females 

 watch over their eggs and lead forth the young in search 

 of food, while the families remain together indefinitely, 

 forming little flocks which include individuals of all ages. 

 When danger threatens, they scatter like frightened sheep 

 and take shelter in crevices of the bark; but they soon 

 reassemble when their alarm subsides. 



The invariable success of the mother-insect in selecting 

 an appropriate spot for egg-laying is very remarkable. 

 Vet the choice is purely instinctive. Impelled by impulses 

 which she can neither ignore nor control, the butterfly 

 forsakes the flowers, and among leaves of a thousand 

 species picks out the one kind which will furnish her 

 fastidious offspring with their ancestral food ; the blood- 

 sucking gnat launches her raft-like egg-mass upon the 

 surface of the water — her larvse being aquatic ; the hover- 

 fly, herself a pollen-feeder, must find aphides for the 

 support of her young. Moreover, the act of oviposition 

 is frequently accompanied by an elaborate ceremonial — 

 as when a leaf is cut and rolled for the reception of the 

 egg (page 122), or when the eggs are implanted deeply 

 in the tissues of a plant (page 204). The sacred beetle 

 watched by Fabre exercises great discrimination in pre- 



