Savory - Arachnida 1977

272 IV. DE ARACHNOLOGIA
exoskeleton glows under the incidence of ultra-violet light; therefore the
scorpion hunter works at night, carrying an ultra-violet lamp with which
to survey his surroundings. Scorpions are then revealed by a greenishyellow
glow. Williams, who has developed this device, reported a
collection of 2,000 scorpions in 4 hr on a Californian sand dune, adding
"At one time seventeen specimens were seen glowing in the light of one
lamp".
Forster and Forster ( 1973) strongly recommend collecting by night,
wearing a battery-powered lamp attached to the forehead. It is thus,
they say, that one sees spiders behaving in a natural manner. Moreover,
spiders' eyes may reflect the light and appear as minute green spots
yards away and before the spiders themselves can be seen.
The underlying importance of all the methods described is the fact
that the different types of habitat are in general occupied by different
species and genera. A scientist therefore takes note of these distinctions
when labelling his collection, and adds, moreover, the month or at
least the season in which a species occupied the habitat from which it
was taken.
PRESERVATION
Arachnida are essentially "spirit-specimens", since their soft bodies
shrivel if allowed to dry. In the traditional method they are kept in
alcohol, the strength of which should not be less than 70%, in small
specimen tubes. A few species will discolour the spirit when first put
into it, so that it may need changing. The brilliant colours of some
specimens may disappear, but in the majority there is no alteration, and
the only problem is the inevitable loss of spirit by evaporation. The
addition of 1% of glycerine is an established way of reducing this and it
also tends to keep the preserved body supple. After the label with the
vital data has been included, the tube is closed with a pellet of cotton
wool, or perhaps more satisfactorily with a plastic cap, and is inverted in
more spirit in a wide-mouthed stoppered bottle. In these conditions an
arachnid can be kept and well preserved for at least 200 years and
probably indefinitely.
Good bottles with ground-glass stoppers are an expensive luxury, and
may be replaced by screw-topped bottles with plastic tops.
For mere exhibition, as in a museum, the hard specimens, like
scorpions and whip scorpions, may be allowed to dry, but as this fixes
their limbs in immovable positions it has disadvantages for other purposes.
The bodies of scorpions become rigid in alcohol or in alcohol
and glycerine, and Williams (1968) recommends an improved formula:
32. PRACTICAL ARACHNOLOGY
Formalin
90% Alcohol
Water
Acetic acid
12%
30%
56%
20' lo
This mixture penetrates and preserves the internal organs, especially
if the scorpion has been killed by dropping it into boiling water.
Whatever method is adopted, loss of alcohol will occur_ albeit
slowly, and specimens not regularly inspected will in time be dry,
except for a residue of glycerine. This leaves the specimen open to
destruction by fungi. There is clearly a need for a better preserving
fluid, and one alternative is isopropyl alcohol. Another, well recommended,
is propylene phenoxytol in a 2% solution. Specimens may be
killed in this; they die with their limbs extended and are then fixed in
alcohol and transferred to the phenoxytol.
ANATOMICAL STUDY
For laboratory investigation of the bodies of Arachnida, three methods
are available. In ordinary circumstances the animal is most easily
examined as it lies in alcohol in a clean white saucer. It may be supported
in the desired position by small pieces of broken porcelain or of
granulated tin. Fine white sand under spirit also holds the specimen
satisfactorily.
A bright, direct illumination is an essential, when the 1-in. objective
will be found to give sufficient magnification for all except
the smallest specimens. Alternatively, the specimens may be allowed
to dry and then examined in the same way but without the alcohol,
and in some cases this is found to be an advantage. A third method is
unorthodox but is most efficient. The specimen is allowed to dry and is
then picked up by one leg with the stage-forceps. The points of the
forceps are brought into focus and illuminated. The animal can now
be turned about and viewed from all angles more easily than in any
other way.
Laboratory examination of the Arachnida also includes dissection
and microtomy. Ordinary naked-eye dissection is almost limited to the
large spiders, scorpions, etc., which are conveniently embedded in wax
for the operation. Reasonable experience in small dissection is necessary,
and it is more than usually desirable that one's scalpel blades shall
be really sharp.
Section-cutting is more specialized work. The exoskeletons of
Arachnida do not allow the rapid entry of fixatives and are hard to
cut. In spiders the difficulty is increased by the fluid nature of the
abdominal contents and the way in which the eggs become unexpectedly
273