176 
BUMBLEBEES 
cells of honey. B. impatiens occurs thru- 
out the eastern United States (Fig. 7). It 
is a subterranean species. A nest taken 
by Franklin, Aug. 31, contained 340 bees, 
of which 4 Avere ^queens and 15 males. It 
was 2V<> feet below the surface of the 
ground. There were 330 unbroken cells, 
the majority of which were queen-cells. 
Another very common species of bumble¬ 
bee is Bombus vagans, which ranges from 
Maine to the eastern Rocky Mountains, and 
southward to Kentucky and North Caro¬ 
lina. According to Franklin the honey- 
pots of American species appear to be 
made not of wax but of pollen grains ce¬ 
mented with propolis. 
THE PARASITIC BUMBLEBEES. 
Many bumblebee colonies are destroyed 
by parasitic or false bumblebees belonging 
to the genus Psithyrus. They are also call¬ 
ed inquiline or guest bumblebees. They 
closely resemble bumblebees in appear¬ 
ance and are both no doubt descended from 
common ancestors. About ten species are 
known in America north of Mexico, and 
three or four more in Mexico and Central 
America. It is a singular fact that not a 
single species is certainly known from 
South America. A common species widely 
distributed in the United States is Ps. 
laboriosus (Fig. 8).' The worker caste is 
entirely absent and only males and females 
are produced. They do not build combs 
nor gather pollen and nectar for their 
young, but live in the nests of the true 
bumblebees, at whose expense their brood 
is reared. 
They were long supposed to be commen¬ 
sals living with the bumblebees and doing 
little harm or possibly of some benefit; but 
much information in regard to the habits 
of two English species has been gained 
thru the observations of Sladen.* Like the 
bumblebees, they hibernate during the win¬ 
ter, but begin to fly a little later in the 
spring. A Psithyrus queen seeks to enter 
the nest of the host bumblebee soon after 
the first brood of workers has appeared. 
Little opposition is then offered by the 
doomed colony, which soon becomes accus¬ 
tomed to her presence. So long as the 
•“'One of these is Ps. vestalis, which dwells ,in the 
nest of B. terrestris. Ps. nshtoni, the representative 
of Ps. vestalis in Eastern Canada, possibly associates 
in the same way with B. terricola. —F. W. L. S'. 
workers are too few to provide ample food 
supplies, the intrduer with instinctive cun¬ 
ning waits until they have become numer¬ 
ous enough to care for herself and her 
brood. As soon as the nest has become 
populous a crisis is precipitated by the 
Psithyrus queen preparing to lay eggs. 
Aroused by this invasion of her rights, the 
bumblebee queen apparently attacks the 
usurper, altho she is doomed beforehand to 
defeat. Protected by a thick tough integu¬ 
ment and armed Avith a larger and more 
curved sting, the parasitic queen invariably 
kills the bumblebee queen. The Psithyrus 
queen is at first compelled to protect her 
eggs from the Bombus workers, but they 
soon care for her brood as faithfully as for 
their own. In Austria tAvo species of 
Psithyrus\ are reported to live amicably 
with their hosts, both producing males 
and females. 
If the Psithyrus queen Avaits too long 
and then enters a colony of the host bum- 
bleblee Avhich has a strong company of 
workers, she is at once furiously assailed 
by overpoAvering numbers; and, altho 
fighting valiantly, is finally slain. Before 
she is destroyed, hoAvever, a dozen or more 
of her assailants are sometimes killed. Tf 
two Psithyrus queens enter the same nest 
they seem neAer to fight Avith each other, 
but one soon goes aAvay. The parasitic 
bumblebees A isit a variety of floAvers, but 
they sIioav a preference for Composites 
like the thorouglnvort and goldenrod which 
are rich in nectar. Their visits are made 
in a leisurely Avay very unlike those of the 
bumblebees. 
The two genera, Bombus and Psithyrus , 
have doubtless been derived from a com¬ 
mon stock. Psithyrus sIioavs evidence of 
degeneration in the loss of the pollen- 
baskets, the smaller eyes, and the untoothed 
mandibles. In explanation of the origin 
of the parasitic habit Sladen points out 
that the queens of several common species 
of Bombus often enter the nests of other 
species of this genus, fight a duel to the 
death with the queen, and if successful 
(which is unusual) lay their eggs and as¬ 
sume the duties of the foundress of the col¬ 
ony. B. terrestris behaves in this Avay in the 
nest of the nearly-related species B. luco- 
fRepresented in .North America liv Ps. laboriosus, 
Ps. insularis, and Ps. fernaldae. — F. W. L. S. 
