red squill on human beings.
Red squill raticides are made from
the bulb of the plant Urginea maritima,
a perennial belonging to the lily family.
There are two commercial varieties of
squill, apparently not distinguishable
botanically. White squill is used in
human medicine, and red squill is used
in raticide preparations. The red squill
rat poison available on the market is
made from the dried and ground bulb
and sold as powdered red squill, or under
various trade names. The use of
liquid extracts of red squill in raticides
is being studied.
Powdered red squill cannot be recommended
at present as a rat poison without
certain reservations, because the
product may vary from a satisfactorily
high toxicity to practically none at all.
In order to obtain a powder of maximum
toxicity it is necessary to dry the red
squill bulbs under controlled temperature
conditions. Some of the squill
powder sold for killing rats has been
manufactured properly and is dependable;
other powder has not, and its
toxicity is extremely uncertain. The
Biological Survey is working toward
a remedy for this situation.
An effort is being made to establish
a standard for powdered red squill with
a minimum lethal dosage of not more
than 400 mg. per kg. of rat. Such a
product, when mixed with food in the
proportion of 1 part squill powder to
16 parts food by weight makes a bait
strong enough for practical purposes.
If the squill were a little weaker it
would have to be mixed with the food
in correspondingly greater proportion,
but if the proportion is much greater
the acceptance of the bait by the rats is
reduced.
In using powdered red squill to destroy
rats, the choice of bait is most
important. The aim is to destrov every
rat with one application; otherwise, the
survivors become suspicious and are
hard to dispose of later. This requires
an ample supply of bait that appeals to
the appetites of the rats. In establishments
where a variety of foods may
be constantly available to the rats, an
effort should first be made to get all
foods out of their reach a few. days
before attempting to poison. A further
help is to prebait with small quantities
64 Jan., 1937
RODENT CONTROL
of unpoisoned foods of the kinds proposed
to be used as bait. If this prebait
is well taken, the poisoning may
follow immediately, but if it is not
taken, there is little use in putting out
poison in the same kind of food. Careful
attention to details of this kind
can be given by an individual in treating
his own premises. In extensive
campaigns involving the treatment of
all premises over considerable areas, it
may be impracticable to prebait because
of the added time and expense. Property
holders in the area,however, are
asked to keep all garbage and food
materials out of reach of rats for a
few days before the campaign.