Just before pupation honeybee larvae cover the walls of their cells with
silk, playing out the fibres randomly so that
by the end of the spinning the walls are covered by thin sheets in which the
individual fibrils are readily discernible. Subsequently the larvae
produce, from the anus, a colourless pollen-free material and then a yellow
pollen-bearing one, both of which are applied in turn to the silk base. 
Nothing further is known of these substances, but
they invite the analogy of a size as in paper manufacture.

There are other, far from subtle, changes in combs. Newly formed combs
of white wax soon yellow, pass through shades of brown and finally become
almost black with age. HUBER (1814) suggested that white and yellow combs
differed mechanically and that propolis (not the source of yellowness), added
to wax, colours it darkly. Inasmuch as propolis is a common constituent in
dark combs, its properties are relevant to the discussion.

CONCLUSIONS

The honeybee nest contains areas for the storage of nectar and pollen and
those for the rearing of brood, either in the same or in different combs. On
re-use over a number of brood cycles, brood comb becomes a composite
material consisting of an elastic element, silk, embedded in a plastic one, wax ;
honey-comb tends to remain monophasic.  

The strength and rigidity of silk is maintained between 25 and 45 °C. 
Native wax is a hydrophobic, isotropic and paracrystalline
plastic whose strength and rigidity greatly decrease with increasing
temperature. Propolis, often added to combs, is mechanically similar to wax
but structurally inferior to it. The elastic and plastic elements behave very
differently with respect to temperature.

Intact brood comb is a planar isotropic silk-wax composite material in
which the silk acts as a fibre reinforcement that greatly improves the overall
mechanical properties of the comb. Inasmuch as honeybees die in droves at
40 °C (FREE and SPENCER-BOOTH, 1958) and the entire nest is likely to fail at
this temperature, the survival of a colony of bees is predicated on thermoregulation.

Hepburn, H. R., & Kurstjens, S. P. (1988). The combs of honeybees as composite materials. Apidologie, 19(1), 25-36.

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