The Ecology of a Sheltered Clay Bank 253 
bees. When they returned from the field on their reg- 
ular day trips, each tumbled precipitously into its own 
hole without exploring the region or seldom trying out 
any of the burrows before finding its own. (Figs. 1 and 
4 show how similar and how close together the burrows 
were). But one evening between 7 and 7:30, when it 
was almost dark and bees were returning home, many 
hesitated and hovered about before the colony and even 
entered several holes before finding their own. Two 
factors may enter into this inability to find their hole, 
viz., the condition of weariness and the failing light. 
This seems to us a logical foregone conclusion, and it 
would be quite superfluous to mention it except for the 
fact that a certain school of investigators argue for a 
sixth sense to serve these Hymenoptera in their homing 
flight or the ability to return home as if by magic. 
(d) Relation to rain. 
All of the mining bees carried water for their excavat- 
ing. Rain helped them substantially by filling the wagon- 
ruts in the road and giving them a supply of water 
nearby. When these puddles dried up, they were obliged 
to go a long way for water, and in some cases they did 
without water or stretched a gulletful over so much 
earth in the burrow that the result was not plastie mud 
that could be shaped into turrets, but crumbly, slightly 
moist pellets that could only be kicked out of the hole. 
The bees did not leave their burrows during a rainy 
spell, and I have never yet seen a mining-bee return to 
the nest during a storm. I did, however, watch five 
Monobia mud-wasps come home during a heavy down- 
pour. They came in at intervals, all dripping wet 
and slow of flight, and crept into their holes. The 
