164 The Naturalist in La Plata. 



frequently to be startled by two or three or more 

 of these wasps rushing towards my face, and con- 

 tinuing hovering before it, loudly buzzing, attending 

 me in my walks about the fields. The reason of 

 this curious proceeding is that the Monedula preys 

 largely on stinging flies, having learnt from expe- 

 rience that the stinging fly will generally neglect 

 its own safety when it has once fastened on a good 

 spot to draw blood from. When a man or horse 

 stands perfectly motionless the wasps take no 

 notice, but the moment any movement is made of 

 hand, tail, or stamping hoof, they rush to the 

 I'escue, expecting to find a stinging fly. On the 

 other hand, the horse has learnt to know and value 

 this fly-scourge, and will stand very quietly with 

 half a dozen loud wasps hovering in an alarming 

 manner close to his head, well knowing that every 

 fly that settles on him will be instantly snatched 

 away, and that the boisterous Monedula is a better 

 protection even than the tail — which, by the way, 

 the horse wears very long in Buenos Ayres. 



I have, in conclusion, to relate an incident I once 

 witnessed, and which does not show the Monedula 

 in a very amiable light. I was leaning over a gate 

 watching one of these wasps feeding on a sun- 

 flower. A small leaf-cutting bee was hurrying 

 about with its shrill busy hum in the vicinity, and 

 in due time came to the sunflower and settled on 

 it. The Monedula became irritated, possibly at the 

 shrill voice and bustling manner of its neighbour, 

 and, after watching it for a few moments on the 

 flower, deliberately rushed at and drove it off. 

 The leaf-cutter quickly returned, however — for bees 



