216 THE HUMBLE-BEE VIII 
5. PSITHYRUS CAMPESTRIS, Panzer. 
QUEEN.—Medium sized ; length 17-18} mm., expanse 
35-38 mm.; sometimes smaller. 
In light specimens the head is black, with a few yellow 
hairs on top ; thorax black, with a wide yellow band in front 
and a rather wide yellow band, often darkened, behind. 
Abdomen black, with the sides of the 3rd segment (except 
at the base), and the sides of the 4th and 5th segments 
yellow. 
This species is very liable to darken: the yellow band 
on the back of the thorax disappears first, then the front 
band on the thorax, and lastly the yellow on the tail. 
Coat rather thinner, and the hairs slightly coarser and 
stiffer than in any other humble-bee. All the segments of 
the abdomen are almost bare in the middle. 
6th segment bare and shining, punctured towards the 
apex. 
The elevations on the 6th ventral segment are rounded and 
wide and together form a V-shaped mark, with a deep division 
in the middle. 
MALE.—Length 15-16 mm., expanse 28-31 mm. 
In light specimens the head is black, with some yellow 
hairs on top; thorax black, with a wide yellow band in front, 
and another wide one behind ; abdomen yellow, with the 2nd 
segment black, but yellow at the edge except in the middle, 
the 6th segment often black in the middle, and the 7th 
segment black. The yellow on the Ist segment is 
obscure. Cf. the male of B. datrezllellus. 
In dark specimens the whole insect is usually black, with 
the exception of the 4th and 5th segments which are deep 
sooty yellow, interrupted in the middle with black. These 
segments too are sometimes black. 
Hairs slightly coarser and slightly stiffer than in any 
other humble-bee. The 6th ventral segment is slightly 
channelled down the middle and bears on either side a tuft 
of long black hairs. 
