is a ball of
earth, bisected by the twig. It is the size of an apricot when the work
of a single insect and of one's fist if several have collaborated; but
this latter case is rare.

Both Bees use the same materials: calcareous clay, mingled with a little
sand and kneaded into a paste with the mason's own saliva. Damp places,
which would facilitate the quarrying and reduce the expenditure of
saliva for mixing the mortar, are scorned by the Mason-bees, who refuse
fresh earth for building even as our own builders refuse plaster and
lime that have long lost their setting-properties. These materials, when
soaked with pure moisture, would not hold properly. What is wanted is a
dry dust, which greedily absorbs the disgorged saliva and forms with the
latter's albuminous elements a sort of readily-hardening Roman cement,
something in short resembling the cement which we obtain with quicklime
and white of egg.

The mortar-quarry which the Sicilian Mason-bee prefers to work is a
frequented highway, whose metal of chalky flints, crushed by the passing
wheels, has become a smooth surface, like a continuous flagstone.
Whether settling on a twig in a hedge or fixing her abode under the
eaves of some rural dwelling, she always goes for her building-materials
to the nearest path or road, without allowing herself to be distracted
from her business by the constant traffic of people and cattle. You
should see the active Bee at work when the road is dazzling white
under the rays of a hot sun. Between the adjoining farm, which is the
building-yard, and the road, in which the mortar is prepared, we hear
the deep hum of the Bees perpetually crossing one another as they go
to and fro. The air seems traversed by incessant trails of smoke, so
straight and rapid is the worker's flight. Those on the way to the nest
carry tiny pellets of mortar, the size of small shot; those who return
at once settle on the driest and hardest spots. Their whole body
aquiver, they scrape with the tips of their mandibles and rake with
their front tarsi to extract atoms of earth and grains of sand, which,
rolled between their teeth, become impregnated with saliva and form
a solid mass. The work is pursued so vigorously that the worker lets
herself be crushed under the feet of the passers-by rather than abandon
her task.

On the other hand, the Mason-bee of the Walls, who seeks solitude,
far from human habitations, rarely shows herself on the beaten paths,
perhaps