SOCIAL AND COMMUNAL LIFE 415 



others appear to feed only on refuse or useless substances 

 in the nest. Some may be of help to their hosts by 

 acting as scavengers. Over one thousand species of these 

 myrmecophilous (ant-loving) and termitophilous (termite- 

 loving) insects have been recorded by collectors as living 

 habitually in the nests of ants and termites. ' ' 



Parasitism. TECHNICAL NOTE. As examples of temporary 

 external parasites find and examine fleas and ticks on dogs and cats, 

 red mites on house-flies and grasshoppers (at the bases of the 

 wings), etc. As examples of permanent external parasites find 

 bird-lice on pigeons or domestic fowls or on other birds. Note the 

 absence of wings and the peculiarly modified body shape of these 

 parasites. Examine a bird-louse under the microscope ; note the ab- 

 sence of compound eyes (it has simple eyes) and absence of wings ; 

 note bits of feathers, its food, in stomach, showing through the 

 body. Find, as examples of internal parasites, intestinal worms or 

 flukes. Examine trichinized pork to see Trichina in muscles. Ex- 

 amine preserved specimens of tapeworms. Collect pupae of some 

 common butterfly or moth and keep them in the schoolroom until 

 either the butterflies or ichneumon flies issue. Some will surely be 

 parasitized, and yield ichneumon flies (parasites) instead of a butter- 

 fly. As examples of degeneration by quiescence examine barnacles 

 (found on outer rocks of seashore at low tide ; easily obtained as 

 preserved specimens by inland schools) and the females of scale- 

 insects. These insects may be found on oleanders (the black scale, 

 Lecanium olece] or fruit-trees (the San Jose scale, Aspidiotus per- 

 niciosus}. Note the great degeneration of the adult female of the 

 San Jose scale ; it has no eyes, antennae, wings, or legs. The 

 young may be found crawling about at certain times of the year ; 

 they have eyes, antennae, and legs. 



In addition to the various ways of living together among 

 animals, already described, namely, the social and com- 

 munal life of individuals of a single species and the com- 

 mensal and symbiotic life of individuals of different species, 

 there is another and very common kind of association 

 among animals. This is the association of parasite and 

 host; the association between two sorts of animals whereby 

 one, the parasite, lives on or in the other, the host, and at 

 the expense of the host. In this association the parasite 

 gains advantages great or small, sometimes even obtain- 

 ing all the necessities of life, while the host gains nothing, 



