THE EUMENIDAE 323 



she was busily engaged in digging her burrow, yet day after 

 day the hole seemed ever unfinished. One evening we de- 

 termined to open it to see if the wasp used it for sleeping- 

 quarters. The first stroke of the trowel revealed three 

 similar nests, all close together in a row. It has always 

 been our custom to place our little markers one inch west 

 of the burrow. A closer examination showed the marker 

 to be just one inch west of the first covered one, while it 

 was three inches west of the open or unfinished one. Hence 

 we have every reason to believe that the one mother had 

 really dug all three, and we had been too dull to perceive that 

 she was not working on the same one all the time. These 

 three nests had but one cell or chamber each. One-celled 

 nests were rare in the previous year as well as this year, in 

 our vicinity. Can it be that this trait of habit or instinct is 

 heritable, that this individual should show a rare trait so 

 persistently in her work ? 



Incidentally, we found the wasp sleeping in the upper 

 part of the unfinished burrow. The sealed chamber be- 

 neath her and the cell of the middle nest contained eggs 

 and green Hespericl caterpillars, sixteen in all, while the 

 oldest and original hole had a full-grown larva together 

 with the remains of one-third of a caterpillar and some 

 excrement. With it in the cell were fifteen white pupal 

 cases of an Hymenopterous parasite, clustered in one cor- 

 ner. Since the larva was full-grown and healthy, and ap- 

 parently had not been disturbed by them, one can only sus- 

 pect that the Hymenoptera had been parasitic upon the 

 caterpillars before their capture, instead of upon the wasp 

 larva. 



The number of caterpillars used by these wasps varies 

 greatly ; occasionally as few as three are tossing about in the 

 compartment, and in other cases the cell is crammed full 

 with eight or ten. We, too, have found that the wasp does 



