Dear BEE-L,
        On April 1 Rune Stenseth wrote:
>
>We are about to start an experiment with heating of hives
>in the spring to increase early strength.<

        I have been experimenting with heating hives on an off for nearly 20
years and I am certain that it is possible to do this in a beneficial way
without having bees swarming out in to the cold and dying as some others
have found.
        The first year I tried this I was advising my daughter on a High
School Biology project. The goal was to see if a direct trade-off could be
made on heat for less honey consumption. Although there were many pitfalls
and near disasters- including having all the bees start to come out into
freezing weather- nevertheless we found a safe way to do it and found that
our heated hive consumed far less honey and survived the winter with a lot
more live bees than a comparison unheated hive of about the same strength.
This was all before the complications of tracheal and varroa mites hit our area.
        Since then I can summarize many other experiments with the following
list of observations and operating principles:
        1) One thing is sure: bees are attracted towards sources of heat.
        2) Don't make sudden changes in the amount of heat being introduced.
Do everything gradually and in small increments. Otherwise the bees will, as
has been suggested, think that Spring has come and rush out to make flights.
        3) I doubt that you should put even a thermostatically controlled
element in the hive in such a way that the bees can surround it. The reason
is that the bees own body heat will quickly shut it off if it is
thermostatically controlled. And if it is not thermostatically controlled
the insulating properties of the bees own bodies will quickly raise the
temperature to the point where the bees begin to get damaged by the heat.
They don't seem to have sense enough to abandon a too warm source- like
moths aroud a candle flame.
        4) Instead I think you should DECOUPLE the heater (and I have tried
both thermostically controlled heaters and uncontrolled heaters) from direct
bee contact. This might consist, for instance of placing the heater in a box
underneath the hive with screened off vent holes in the bottom board to
allow the heat to come up and envelope the cluster. The thermostat could be
located near the top of the heater box and screened off from bee contact by
the screening in the vent holes. You would primarily be controllin the
temperature of the heater box itself.
        5) Only about 10-20 Watts are required if you are efficient in
delivering the heat to the bees. You can see that this is so by converting
the Calories in the maybe 50 pounds of honey that you wish to conserve into
its Joule equivalent and comparing to how many Joules (Watt-seconds) you
would need in a typical winter heating season.
        6) If instead of a bottom board with vent holes you use a solid
board-such as a sheet of thin Aluminum (for efficient thermal transfer) you
may find a temperature stratification such that the bottom of the hive is
much warmer than the top. In that case I have found that although the bees
will quickly congregate in the hotter regions they will feel much more
confined. They will raise brood if it is warm enough. I have seen SWARM
CELLS in January with snow on the ground. ( I had made double paned
observing windows which permitted me to see this.)
        7) I have used light bulbs most often as heaters. Two 40 bulbs wired
IN SERIES will last forever and produce a total of only 20 Watts. I have not
observed adverse behavior effects of the light (which the bees can see
through the bottom holes) altering bee behavior, although that is a
possibility. The heated air coming off the bulbs is very hot and will
quickly be convected upwards towards the top of the hive which maybe
accounts for less temperature stratification with this arrangement than with
a solid sheet bottom board.
        8) This arrangement works even better (uses less electricity) if the
whole hive and heater box are insulated. There should be a vent hole/bee
escape hole near the top of the hive in addition to the regular constricted
bottom entrance. And probably there should be a way to draw off moisture at
the top. I use an additional hive body sitting on a fiberboard (Homosote
board) top (instead of the usual inner cover) and the hive body is filled
with fiberglas insulation. The fiberboard is sitting on a thin spacer rim so
that the bees can roam around on the top bars. If desired a small bee access
hole can be made through the fiberboard to permit an inverted feeder pail to
be inserted under the fiberglas insulation.
        9) Having a top box with Homosote underneath and a feeder pail
inside under a blanket of fiberglas insulation works so well that in recent
years I have stopped heating hives and have mostly experimented with various
forms of this arrangement (not even bothering to use an outside blanket of
insulation-just using the insulating top box). I have been able to
overwinter single brood chambers with this arrangement with consumption of
only about 20 pounds of honey plus about one to two gallons of sugar water.
This in contrast to the traditional double brood box for our area containing
maybe 80-100 pounds of honey for overwintering. If the access hole through
the Homosote is large enough (maybe two inches in dia.) the whole fiberglas
covered feeder pail will be maintained at a temperature of about 50 deg. F
by the bees own heat- even when the outside temperature goes to minus twenty
degrees. They cluster around this warm syrup source tenaciously and will
hang from the feeder pail in a tight cluster if it is opened and lifted out
in the winter. (You can break the cluster loose by sliding a thin sheet of
carboard under the feeder before lifting it out.)
        10) But don't let this last result deter you from a hive heating
experiment. One additional advantage of hive heating is that you can
introduce menthol packets in the Spring on the heated bottom board if you
suspect an infestation of tracheal mites. Ordinarily the menthol packets
would not be effective in our area (Massachusetts) in the Spring because it
is too cold to evaporate the menthol. And an additional benefit is that you
can start up Spring Nucs on a heater box without worrying about a cold snap
killing off the brood.
                                        Good Luck
                                                Ernie Huber