An Introduction to Solitary Bees
There are an estimated 20,000 species of bees worldwide and the
majority are solitary bees. Because of their solitary lifestyle these
bees do not defend their nests, and although some are physically capable
of stinging they will generally not do so unless roughly handled. This
makes solitary bees a relatively safe model organism to facilitate
lessons on biology, plant/insect interactions, ecology and more.
The solitary bee female mates with a male and then begins her nest.
In natural settings solitary bees burrow in the ground or nest in
preexisting cavities such as beetle burrows, holes made by woodpeckers,
hollow stems and reeds, even empty snail shells! The size of the cavity,
material, orientation and other factors dictate the suitability of the
cavity for different species of solitary bees.
Many solitary bees nest in preexisting cavities in plant material
such as hollow reeds, stems, branches and in holes created by
wood-boring insects. Wood-nesting, solitary bee females mate, then look
for the perfect sized hole in which to make their nest. They collect
pollen and nectar from flowering plants, then use this to stock the hole
with food for their offspring, lay an egg on the pollen/nectar ball and
then create a cell by sealing off the egg with its provision. They
continue this process until the hole is filled with cells, at which
point they seal their nest and then search for another hole in which to
begin another nest.
Different bees use different materials to seal their nests. As their
name suggests, the leaf cutter bee cuts semi-circle pieces from leaves
to line the inner cavity of the nest, create individual cells and cap
off the nest. The mason bee uses mud to create a cement-like seal
between the cells. Some solitary bees use flower petals, others use
plant resins or fibers. The Hawaiian yellow-faced bees secrete a
waterproof cellophane-like material to line their cavities and seal
their cells.
Meanwhile, the eggs she laid develop into larva that look like
legless caterpillars. These larvae eat and grow until they are ready to
pupate. In the pupal stage, the bee goes through similar development to
the caterpillar in a cocoon. The bee pupa looks more like an adult bee,
but it doesn’t move much, and its wings and other features might not be
visible. When the pupal stage is complete, an adult bee will emerge from
the pupal skin. The adult bee then finds a mate and continues the
cycle.