These cuckoos live at the expense of their hosts. The mother of the
industrial brood makes her cell and provisions it, and lays her egg. The
cuckoo bee manages to enter also and lay her egg in the same cell, the
usual result being that the cuckoo devours most of the food instead of the
rightful offspring, which gradually gets starved and dies, the cuckoo
appearing in its place; but there have been cases, how frequent they are is
difficult to say, in which both offsprings have emerged.
The whole problem of the relationships between host and cuckoo is most
interesting. In some cases the cuckoos are so like their hosts that it is
difficult to tell one from the other, in others they are so unlike that it
is difficult to trace any resemblance between them. There are a great
number of different kinds of cuckoos, and most of them select a special
host to associate {15} with, and are never found except with that species.
There are, however, cases of cuckoos which visit the nests of more than one
host, and cases of hosts which are visited by several kinds of cuckoos. In
the short-tongued bees, with the exception of _Halictus_ and _Sphecodes_,
the cuckoos are quite unlike their hosts both in form and colour. In the
_Andrenas_ (the lawn bee being one of them) the hosts are clothed with
reddish, or brown and black, hairs, and are of a more or less stout build
(pl. B, 15, 16). The cuckoos are elegant in shape, almost devoid of hairs,
and most of them are striped with yellow or brown across the body so that
they present a wasp-like appearance (pl. B, 18). Species more unlike one
another than host and cuckoo one could hardly imagine; still this stranger
seems to get access to the nest of its host without opposition. In a colony
of _Andrena_ one may see the cuckoos (which rejoice in the name of _Nomada_
or wanderers) flying about among the females of the industrious bee, and no
alarm or concern appears to be felt by the latter. As we go up in the scale
of bees, i.e. towards the more specialized, and arrive at those with longer
tongues, the {16} cuckoos are found as a rule to resemble their hosts more
closely, both in colour and structure, and when we reach the social genus
_Bombus_ (i.e. the humble bees) we find the cuckoos so like their hosts
(pl. D, 30, 31) that even entomologists of experience mistake one for the
other. _Apis_ (the hive bee) has no cuckoo. It seems to be theoretically
probable that both cuckoo and host once originated from common parents;
this is suggested by the similarity of structure of certain parts of both
host and cuckoo, even in cases where they are otherwise most dissimilar.
_Andrena_ and _Nomada_, for instance, which are very unlike, as stated
above, agree in both having very feeble stings and in possessing three
conspicuous spines on the upper and posterior edge of the orbit of the
larva. Also, although _Andrena_ the host has a short tongue, and _Nomada_,
its cuckoo, a long one, the appendages (_labial palpi_) of the latter's
tongue are framed on the same plan as those of the tongue of _Andrena_, and
are quite unlike those of the other long-tongued bees. On the other hand,
the cuckoos of the social species resemble them so closely in structure as
well as {17} appearance that it is more necessary to search for points of
difference than of similarity. There is only one case known of a cuckoo
wasp, and that resembles its host even more closely than do the cuckoos of
the humble bees. All these points certainly suggest the probability that
the social bees and wasps and their cuckoos adopted different habits at a
much more recent date than the solitary species, and therefore have not had
so much time to become differentiated in structure. The only short-tongued
bees which have cuckoos of similar structure are the species of _Halictus_
(pl. B, 12); their cuckoos, _Sphecodes_ (pl. B, 11), are closely allied to
them, but then _Halictus_ and _Sphecodes_ are most peculiar genera;
although short-tongued, their females spend the winter in the earth, as do
the social bees and wasps (see p. 13), and they colonize largely, which may
prove to be a step towards socialism.
* * * * *
{18}