NO. I BLACK FLIES OF GUATEMALA — DALMAT 33 



huts, creates no barrier for insects that wish to enter. In most litera- 

 ture mentioning the habits of the black flies it is claimed that the adult 

 flies do not often enter buildings (Bequaert, 1934, p. 195). However, 

 I have commonly found them in goodly numbers within buildings, 

 where they will readily bite. They are active in the laboratory build- 

 ings during the day and also at night when there is sufficient light. 

 Their presence indoors was already mentioned in the section on the 

 "Importance of the Simuliidae." 



Of considerable importance in a discussion of the possible spread 

 of onchocerciasis is the migratory worker. In the region of Yepocapa 

 the majority of temporary workers (cuadrilleros) hired during the 

 harvest and processing season come from the Department of El 

 Quiche, in the north-central region of the country. Large parts of 

 this department are located at altitudes comparable to those in the 

 onchocerciasis zone and have meteorological conditions, stream types, 

 crops, and Simulium species that are typical of that zone. These work- 

 ers, with all their families, arrive at the fincas in Yepocapa and remain 

 there for 4 or 5 months. As shown by medical examinations, a good 

 number of these individuals become infected with Onchocerca. How- 

 ever, no endemic zone has been established in El Quiche by the re- 

 turning workers. Besides Simulium ochraceum and Simulium metal- 

 licum, Simulium veracrusanufii, which has been proved experimen- 

 tally to be an excellent potential vector (Gibson and Dalmat, 1952), 

 is present in abundance in El Quiche. It is believed that the failure 

 of the disease to become endemic in this region may be explained by 

 the wide dispersion of the people, who are primarily pastoral and live 

 in isolated family groups. Under these conditions the flies do not 

 come into sufficient contact with man to transmit the disease effec- 

 tively. However, it is possible that the proper combination of factors 

 at some particular time might bring about the beginning of an en- 

 demic zone in that region. The same is undoubtedly true of other 

 areas from which transient laborers are hired for work on the coffee 

 fincas in the onchocerciasis zones. 



Another possible source of extension of the disease from its present 

 confines is the itinerant salesman. To earn money for his minor pur- 

 chases the man may buy various items in one locality and carry them 

 on his back (pi. 9, fig. i) for surprising distances, sometimes over 

 100 miles, for resale in another locality. Also, he will often carry 

 additional items for sale that he or his wife has made. The Indian 

 thinks nothing of carrying loads up to and even surpassing 200 pounds 

 in that manner. Much of his wares is carried in a wooden-framed 

 pack (cacaste) which is strapped to his back and also supported by a 



