the pages of 'The British Tarantula Society Journal'
Dr. Robert Bustard
Humidity appears to be the most
misunderstood factor in the tarantula keeping equation.
Many people with small collections - and this must
include most beginners - cannot justify heating a space
for their tarantulas which is perhaps ideal. So they
(mostly) resort to heat mats.
I find from my correspondence that invariably beginners
place the heat mats underneath the tank. This results in
a number of problems fully dealt with in Alan Stillwell
in an admirable, two-part article "So you want to
keep a tarantula?" in 'Insect World' Vol. 1 parts 1
& 2 (1995). Here we are only concerned with the
humidity aspects which, as Alan Stillwell correctly
states, can be overcome by fixing the heating pad to the
back cover or side of the tank.
I always recommend a peat base to the tank. Clearly for
tarantulas this has to be a minimum of half an inch
(12mm) deep, and more usually at least an inch (25mm)
deep. The instructions with heat mats clearly state that
you should not use a covering layer of "more than a
thin (5mm) thickness of base medium." As pointed out
by Alan Stillwell, if you use Vermiculite that is an even
more efficient insulator (preventing the heat from rising
into the tank).
The effect of a heat mat below even slightly moistened
peat is that it will drive the moisture out of the peat.
The resultant water vapour will, on reaching the cooler
lid of the container, condense to drip back into the
substrate. This constant recycling of the moisture
contained in the peat substrate will ensure that the
humidity in the tank is a constant 100% which is totally
unsuitable for your tarantula irrespective of it's
habitat preferences. When a tank has been set up and
allowed to stabilise, if there is a lot of water
condensing on the sides of the tank, then the humidity
therein is 100% (exceptions are where the room
temperature has suddenly dropped or is greatly below tank
Having set up your tank it is a good idea to allow the
peat substrate to at least partially dry out at one end
and only spray about one half of the tank. This will
allow the spider to choose it's substrate humidity by
shuttling across the tank. I have found this technique
very useful when rearing baby Theraphosa blondi, which
invariably choose to moult at the dry end.
Ventilation is also invaluable. It will reduce the
humidity (which, if it falls too far can be increased by
more spraying). Most importantly, it will provide air
movement which is so crucial for the successful keeping
of many arboreal species which will not flourish in (too)
humid, stagnant air. I tell beginners that you should be
able to grow a plant in arboreal spiders' tanks. If the
plant dies from 'damping off the air is too
humid/stagnant for the tarantula.
I have recently written a detailed humidity guide for
beginners. At Ann Webb's suggestion, when revised, I will
offer it to the Journal for a lot of our losses are due
to too high humidity, often combined with too stagnant
air. This is fatal for eggsacs.
Again I find that many people have little idea of
humidity levels and the compact mini-temperature and
humidity gauges can prove invaluable.
I would fniish by underlining a comment of Alan Stillwell
in his excellent article referred to above. If put along
the back of the tank the heat mat should not cover the
whole length of the tank (one half or so should be
adequate) so that the spider can move to a cooler area if
it becomes overheated. A sheet of polystyrene should be
placed behind the heat mat to direct the heat forwards
into the tank.
© Copyright 'The British Tarantula
Last Updated: February 12, 2007