1 82 A YEAR OF COSTA RFC AN NATURAL HISTORY 



wasp. It was a female, five-eighths of an Inch (i6 mm.) 

 long, shining bluish-black with a bright yellow spot on the 

 scutellum (hind part of the thorax) and a pair of yellow spots 

 on each of the second and third abdominal segments. The 

 head was relatively large, hemispherical and chiefly occu- 

 pied by the eyes. The wings were smoky. This species 

 is found also throughout much of South America. As the 

 larvae of Eristalis (a genus occurring throughout the world) 

 are known to live "in decaying vegetable matter, manure or 

 in soft mud impregnated with decaying vegetable matter" 

 (Williston), possibly the larvae of E. scutellaris may feed on 

 the decaying leaf-fragments gathered by the ants. 



A few yards from the beginning of the zigzag road down 

 to the Reventazon were, in June and late July, two streams 

 of numerous leaf-cutters crossing the road, but on Septem- 

 ber 29 there was only one stream composed of very few in- 

 dividuals. At this time of year, therefore, there seemed to 

 be a marked decrease in the ants' activities in a number of 

 nests at Juan Vinas. 



Without having given special attention to the distribu- 

 tion of the leaf-cutters in Costa Rica, our notes mention 

 them as occurring not far from a swamp near Paraiso, where 

 were two nests near the railroad track at about 4400 feet 

 elevation. Into one of these, on October 11, the ants were 

 carrying many more bits of plants than was the case at Juan 

 Vinas twelve days earlier. Again, south of the Paraiso 

 road and nearer to Cartago, we came, on October 26, upon 

 a large leaf-cutters' nest directly in the road, which was in 

 process of being moved around the nest by trails made by 

 horses and mules to avoid it. A.'s horse shied and showed 

 uneasiness until he was safely past, evidently fearing the 

 ground would crumble or his feet sink into holes. This 

 colony was vigorous and flourishing, to judge from its size 

 and the trails leading to it, and was located less than 500 



