This week at my bee course we went through the process of treating the bees for the varroa mites as this is a big problem here in Switzerland, as it is world wide.
For the summer treatment we used Formic Acid in an easy to use compact Liebig Dispenser.
The bees were awfully aggressive and I got stung twice, so at the moment I have a wonderfully crease-free left hand, twice the size as normal - at least it should work wonders in the carpal tunnel department ;)
For the bees this is quite a stressing time and the colonies that were treated tended to hang outside the hives as I am sure the gases bother them quite badly too.
If you are a beekeeper when do you treat your bees?
Do you treat them twice yearly?
What do you treat your colonies with?