I believe that Peter is correct in that the darkening of brood combs is from
the larval meconium (defecation), which is smeared into the silk cocoon.
Note that the silk cocoon, meconium, and subsequent varnishing with propolis
may help to seal in pathogen spores between rounds of brood.

Does anyone know what travel stain is?
>
No, but it is largely water soluble, so I do not think that it is all
propolis.

>
> Also, when hives are robbed, there is a sort of 'mud' left on the entrance
> holes.
>
Don't know, but always suspected sticky feet from the frenzy of stealing
honey.

Randy Oliver

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