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 
rescue, 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 imstantly 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 hght. 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 
