Extreme care should be exercised in handling poisons in rodent-control work. Prepared poisons should be placed in strong, properly labeled containers and should be distributed only to assistants working under the direct supervision of bureau leaders or to responsible cooperators.
Strychnine (in the alkaloid form) is the poison most largely used in rodent-control, its speedy action making it one of the most humane. Moreover, numerous tests have shown that in the quantities employed in control operations strychnine is relatively harmless to such gallinaceous birds as quail, pheasants, grouse, and domestic chickens. The smaller birds also are safeguarded because of the fact that the grains used in poisoned baits are of the large-kerneled kinds, such as oats, and contain a minimum of weed seeds and cracked kernels. Furthermore, in a large portion of the baits used the kernels are steamed, rolled, and flattened so that their increased size lessens their attractiveness to the smaller birds.
The use of red squill in the control of house rats and mice is recommended, as it is an effective and specific poison for these rodents and relatively harmless to other forms of animal life.
The use of thallium in rodent-control will in some places succeed where strychnine alone fails. It should not be used, however, except to a very limited extent in follow-up operations against ground squirrels, prairie dogs, and rats. Such limited use of thallium should be guarded with the greatest care under close and fully competent supervision, as it is extremely dangerous to all life. Though thallium is highly effective in destroying rodents, it can not be overemphasized that this poison is not to be recommended for general use, except to supplement strychnine in follow-up work. It should never be handled without careful consideration in each particular case of all the potential dangers involved.
Arsenic, cyanides, and phosphorus should not be used or recommended for rodent-control, as they are not now known to have any special advantages, and furthermore they may be a menace to other forms of animal life. Not only is phosphorus dangerous to beneficial wild life, but it is particularly unsafe because it sometimes causes fire.
Poisonous gases, which are efficient in the fumigation of burrows, grain bins, and garbage dumps, should be used only by trained and experienced workers in rodent-control.
Poisoning operations for the control of predatory animals should be limited strictly to areas where there is urgent need. They will not be undertaken under the direction of the Biological Survey where trapping or other means of control are practicable and the cost is not prohibitive.