62 THE HUMBLE-BEE 11 
for the extra thick skin, many thick-hided animals 
lacking hair. Their stings are stouter and more 
curved than those of Aomdus: it is interesting to 
note that the sting in the queen honey-bee, who 
also uses it for killing queens, is curved, while in 
the worker honey-bee the sting is straight. 
The movements of the Pszthyrus, whether flying 
or walking, are lethargic and awkward. When 
visiting the flowers in search of food she does not 
travel systematically from blossom to blossom like 
an industrious humble-bee, but settling upon a 
bloom she sips lazily sufficient nectar to satisfy her 
immediate need, and afterwards is very likely to 
become drowsy. Fatigued by the exertion of 
obtaining food for herself, she is plainly incapable 
of the sustained effort that would be needed had 
she to provide for the wants of her young. 
Whenever the weather is pleasant she searches 
leisurely for a nest of the particular species of 
Bombus which it is her instinct to victimise. In 
this work she is guided, like a dog, largely by 
scent. In May 1895 I caught a searching queen 
of Ps. vestalis and put her into a glass jar in which 
I had kept some queens of its host, 2. ¢errestris, 
for several hours, so that the jar had acquired the 
characteristic odour of this bee. The Pszthyrus 
queen ran about inside the jar in great excite- 
ment, waving her antenne and stroking the in- 
terior of the jar with them, apparently trying to 
trace the path the queens had taken. After a few 
minutes’ hunting she flew out of the jar, but finding 
