26 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 134 
About go species of nonpathogenic protozoa have been found in 
cockroaches. Approximately half of these are found in the wood- 
feeding cockroaches, Cryptocercus and Panesthia. Although interest- 
ing, the nonpathogenic forms are beyond the scope of this review. 
It becomes more and more evident that eating roaches is a 
very bad habit for animals that habitually indulge in it. 
CHANDLER (1949). 
VII. HELMINTHS 
Cockroaches are known to harbor a fairly large number of hel- 
minths, some of which may occur as primary parasites of man and 
other vertebrates (Appendix E). 
Next to the bacteria, the helminths form the largest group of 
pathogenic organisms transmitted by cockroaches. The eggs of seven 
species of helminths have been found naturally in cockroaches; eggs 
of five other species were passed unharmed through the guts of 
cockroaches and appeared in their feces. Cockroaches have been found 
to serve naturally as the intermediate hosts of 12 species of helminths 
and as the experimental intermediate hosts of 11 other species. Four 
doubtful records are listed and discussed. Attempts to infect cock- 
roaches experimentally with three cestodes and five nematodes were 
completely negative. About 45 species of helminths that are primary 
parasites of cokroaches and not pathogenic to vertebrates are known. 
These are not discussed. 
Some cockroaches have been found to serve as excellent experi- 
mental hosts in studies on the life histories of various parasitic worms 
(Hall, 1929). It is this ability to support the development of certain 
species of helminths, especially spirurids and acanthocephalids in 
nature, that makes cockroaches potentially dangerous. The develop- 
ment of species of Gongylonema, primary parasites of sheep, cattle, 
and horses, as accidental parasites in cockroaches is an example of 
cockroaches serving as hosts for worms that cannot depend on such 
hosts for transmission in nature (Hall, 1929). 
The finding of Protospirura columbiana in rats killed in the National 
Zoological Park in Washington, D. C., but not in rats caught in other 
parts of the city suggested to Cram (1926) that the normal host of 
this spirurid may be a rodent other than the rat present in the park. 
Cram suggested that rats and cockroaches, commonly present in 
zoological gardens, may play a part in the dissemination of parasites 
not native to a country but brought into zoos with exhibition animals. 
