The life-history of an ordinary pair of solitary bees is, roughly, as
follows: I will take for an example one of the spring species of _Andrena_.
Many people know the little red bee, which for some apparently
unaccountable reason suddenly appears in myriads on their lawn or gravel
path, throwing up little mounds of finely powdered earth--in this respect
being quite different from worm casts, which are formed of wet mould and
the particles of which cling together--sometimes causing considerable alarm
as to the possible effect on the lawn. These have hatched out from burrows
made by their parents in the previous year, the mouths of which have been
filled up with earth and therefore are quite invisible till the newly
fledged bees gnaw their way out. They, in their turn, are now making fresh
burrows for their own broods; possibly they infested some one else's lawn
the year before or were only in comparatively small {10} numbers on the
lawn under notice and so passed unrecognized. They may safely be left
alone, as they never seem to breed many consecutive years in one such
locality: probably the treatment of a lawn does not suit them, mowing and
rolling upsetting their arrangements. We will now consider these
arrangements. The female bee, so soon as she realizes that she is charged
with the duty of providing for her future offspring, makes a burrow in the
ground, and the earth thrown up from the tunnel forms the little heap which
is so observable; this burrow varies in depth from 6 to 12 inches and has
short lateral branches; each of these she shapes, more or less, into the
form of a cell, provisions it with a small mass of pollen mixed with honey
for the maintenance of the larva when hatched, and lays her egg; she then
seals up that cell and proceeds to the next, and in this way fills the
burrow up until pretty near the surface. The bee caterpillar when hatched
is a white grub-like creature which, after devouring the food provided for
it, becomes more or less torpid; it then makes its final change of skin,
after how long a period is probably uncertain, and appears in the nymph
stage. {11} [Illustration: FIG. 1. Bombus, larva and nymph: after Packard.]
This stage corresponds to the chrysalis of a moth or butterfly, the
creature being shortened up and rather more like the perfect insect
compacted into the smallest form possible. People are often misled into the
idea that the caterpillar forms the chrysalis over its former self, whereas
the chrysalis has been all the time forming inside the caterpillar and only
shows itself when the final skin is shed; of course some caterpillars spin
a cocoon over themselves before they change their skin, but then the true
chrysalis is found inside the cocoon. A curious fact connected with the
change from the nymph to the perfect insect is that this takes place
sometimes as early as August in the year preceding their appearance; so
that cells dug up in August may contain fully fledged insects which are not
due to appear till April or May of the following year. It is wonderful also
how long life can be {12} sustained by these creatures in the "full-fed
larva" condition. Some years ago I collected a number of pierced bramble
stems in order to breed out some of the small "sandwasps" which nest in
them. On opening them in May, when the perfect insects are generally ready
to appear, I found that several of the larvae had rather shrunk up and had
not changed into nymphs. These I left in the stems, covering them up again,
and they appeared as perfect insects in the May of the following year.
The account given of the nesting habits of the above _Andrena_ of our
lawns, etc., is more or less true of nearly all the solitary bees. Their
methods vary, some burrow in the ground, some in old wood, some in snail
shells, some in bramble stems or straws or the hollow stems of various
plants, some in holes or crevices in walls, etc., and their methods of
building their cells vary exceedingly: all of these are of great interest
and some display an ingenuity which is quite surprising. Of these special
nesting habits some of the most striking will be mentioned later on.
Before leaving these general remarks on the {13} solitary bees the habits
of two genera must be specially noticed, as they differ in an essential
point from those of the others. These are known to entomologists under the
names of _Halictus_ and _Sphecodes_.
In most species of these the males and females of the new brood are not
hatched out till after midsummer, and no work is done for the provisioning
of new burrows that autumn; but the female, after having undertaken the
duties of maternity, hibernates, i.e. goes back into a burrow and lives
there till the next spring, the males dying off before the winter. In the
spring the [female] wakes up and does the necessary work for the future
brood just as any ordinary spring bee would--but there are no attendant
males--the duties of that sex having been performed in the autumn. The
larvae contained in these burrows hatch out after midsummer and therefore
never spend a winter in the ground. In this respect they resemble the
social bees and wasps, about which more hereafter; in the meanwhile a few
words must be said about the cuckoos or inquilines, which are perhaps the
most interesting creatures of all.
* * * * *
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