revealed at once. There are cells whose provisions, at least a
year old, are intact, but dried up or musty, because the egg has never
developed. There are others containing a dead larva, reduced by time
to a blackened, curled-up cylinder. There are some whence the perfect
insect was never able to issue: the Chalicodoma wore herself out in
trying to pierce the ceiling of her chamber; her strength failed her and
she perished in the attempt. Others again and very many are occupied
by ravagers, Leucopses (Cf. "The Mason-bees": chapter 11.--Translator's
Note.) and Anthrax-flies, who will come out a good deal later, in July.
Altogether, the house is far from having every room vacant; there are
nearly always a considerable number occupied either by parasites that
were still in the egg-stage at the time when the Mason-bee was at work
or by damaged provisions, dried grubs or Chalicodomae in the perfect
state who have died without being able to effect their deliverance.

Should all the rooms be available, a rare occurrence, there still
remains a method of distinguishing between an ancient nest and a recent
one. The cocoon, as I have said, adheres pretty closely to the walls;
and the mother does not always take away this remnant, either
because she is unable to do so, or because she considers the removal
unnecessary. Thus the base of the new cocoon is set in the bottom of the
old cocoon. This double wrapper points very clearly to two generations,
two separate years. I have even found as many as three cocoons fitting
one into another at their bases. Consequently, the nests of the
Mason-bee of the Pebbles are able to do duty for three years, if not
more. Eventually they become utter ruins, abandoned to the Spiders and
to various smaller Bees or Wasps, who take up their quarters in the
crumbling rooms.

As we see, an old nest is hardly ever capable of containing the
Mason-bee's entire laying, which calls for some fifteen apartments. The
number of rooms at her disposal is most unequal, but always very small.
It is saying much when there are enough to receive about half the
laying. Four or five cells, sometimes two or even one: that is what
the Mason usually finds in a nest that is not her own work. This large
reduction is explained when we remember the numerous parasites that live
upon the unfortunate Bee.

Now, how are the sexes distributed in those layings which are
necessarily broken up between one old nest and another? They are