The Mason- Wasps 



On the side-wall, under the chimneypiece, 

 I hung a thermometer over a Pelopaeus- 

 nest. During an hour's observation, with 

 a fire giving out a moderate heat, it fluctu- 

 ated between 95° and 105° F. This tem- 

 perature, it is true, does not remain the 

 same during the long larval period; on the 

 contrary, it varies greatly, according to the 

 season of the year and the time of day. I 

 wanted something better and I found it on 

 two occasions. 



My first observation was made in the 

 engine-room of a silk-factory. The back 

 of the boiler reached nearly to the ceiling, 

 the space between being barely twenty 

 inches. It was against this ceiling, right 

 above the huge cauldron, which was always 

 full of water and steam at a high tem- 

 perature, that the Pelopaeus-nest was fixed. 

 At this spot the thermometer marked 120°. 

 This degree of heat was maintained all 

 through the year; it was only at night and 

 on holidays that it decreased. 



A country distillery furnished me with 

 the second subject of observation. It 

 combined two excellent conditions for at- 

 tracting Pelopaei : rural quiet and the heat 

 of a furnace. The nests therefore were 

 numerous, fixed more or less everywhere on 

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