Within the pest control industry, rat bait generally refers to the use of poisons to kill rats.
Toxic substances, often scented and flavored to appeal to the rodents are set out in traps or stations. The rats ingest the products and die—a process that can take up to a week to occur.
There are non-toxic rat baits as well, which are used primarily to lure the rat into a trap to be killed, or into a live capture trap from which the animal is later released.
Non-toxic rat baits
Rats are amazingly canny and cautious creatures with a powerful sense of smell and an acute sense of taste; baiting rats can be challenging in the extreme as a result of these characteristics. Rats are also adept at freeing easily portable types of food from snap traps without activating the mechanism. They avoid “new” objects in their environment and have been observed “testing” food sources by ingesting small amounts and waiting to see if they grow sick before eating more.
Non-toxic baits are generally used to lure rats into traps, be they the classic snap trap; other lethal types of traps or capture and release devices.
Because rats are scavengers by nature the most effective rat attractants are food baits; some of the most successful (depending on the species of rat) of these are:
• Peanut butter: Whether creamy or chunky, the taste and smell of this childhood food favorite is irresistible to rats. Peanut butter has the added benefit of being difficult to remove from a trap, unlike a seed or cheese morsel which may be snatched and carried off to be eaten. The consistency of peanut butter when placed strategically in a trap forces the rat to stay at the bait to ingest it. Peanut butter is particularly efficacious when used in concert with snap-traps
• Fruits and vegetables are particularly appealing to roof rats. Because of high rates of spoilage these baits must be changed out frequently, a rat will not approach or eat rotting or spoiled foods.
• Meats and fish are attractive to the Norway rat, but if used must be swapped out frequently and not used in traps to be placed in locations unreachable by humans.
• Seeds, particularly pumpkin seeds are known rat attractants but must be carefully placed as they are easy for the rats to snatch from the trap without activating the mechanism.
• Dog food is usually irresistible to rats; dry foods may be liberated from traps, a dab of canned food must be changed out frequently to avoid spoilage. Canned food, like peanut butter is less portable and more likely to keep the rat eating in place.
• Bacon is nearly as mouthwatering to rats as it is humans, whether offered alone or mixed into peanut butter, dog food or other bait mixtures.
There is some strategy involved when using food baits. It is more effective if a trap put out but is not set for several days while baited; this will accustom the rats to eating safely at the trap location reducing the incidence of “trap shyness”. Baited traps should be placed in or along the rat’s regular line of travel (detectable from droppings and urine stains); rats are cautious and will not break their normal routine to investigate even the most attractive baits.
The use of nesting materials as bait has also proven effective. Cotton balls dipped in vanilla extract are said to be particularly attractive to female rats; other soft materials work equally as well. The trick is securing the cloth, cotton ball or string to the trap in such a way that it will lure the animal in close enough to activate the mechanism and not just be snatched away.
The Middle Ground
1) Instant potato flakes set out along a rat trail with small bowl of water nearby is said to be a highly successful non-toxic way to eliminate rats. The theory is that the rats eat the dry potato flakes, which induces thirst; the rats will then drink the water. The potato flakes expand in the rat stomach, causing the stomach to rupture, killing the animal.There is anecdotal evidence that it is possible to kill rats without a trap or the use of poisons. While little authoritative information is available on the efficacy of these methods, many people swear by them. One of these methods (cement powder and corn-flour) has even been found on a rat bait website maintained by the government of Australia
2) Based on the same theory, a mixture of equal parts flour, sugar and baking soda placed on small disposable plates laced with peanut butter on the edges will cause a fatal buildup of carbon dioxide when the ingested mixture mixes with stomach fluids.
3) Another option is to mix corn-flour and dry cement powder and place the mixture in dishes along the rat paths. The effect is said to be the same as use of potato flakes, the mixture induces thirst and drinking additional water ensures the cement powder reacts becoming an indigestible mass in the stomach of the rat.
An issue with these non-toxic rat killers is the fact that the rat will not necessarily die where the bait has been placed, but may return to a nest or crawl away to die inside walls or other areas inaccessible to humans. The theory expressed in defense of this point is that the thirst inducing methods will drive the rats to find outside water sources, but there is no guarantee this will occur.
Poison Rat Baits
In times past one had only to pop down to the nearest general store and a choice of rat poisons was readily available to purchase. Arsenic, strychnine, thallium and cyanide have all been used at some point in history as rat poisons. As these substances became regulated and illegal to possess due to their great toxicity to humans, other presumably safer poisons have been introduced in their wake.
Anti-coagulants block the metabolic cycle of Vitamin K, an important factor in blood clot formation. When ingested in sufficient quantity, this class of rat bait induces massive internal hemorrhage and eventually, death.Anti-coagulant substances such as Warfarin (also known as Coumadin) were popular first generation rat baits. In fact, Warfarin was first developed in 1948 as a rat and mouse poison, only later was it found to be a helpful medication for humans prone to thrombosis and thromboembolism.
1) First generation anti-coagulant rat baits (Coumadin, Warfarin) are classed as chronic, meaning that the effects develop gradually and are dependent on several feedings to reach levels toxic to the rats. It can take a first generation anti-coagulant up to a week to kill the animal. In some respects this was considered an advantage, as rats were less likely to associate illness with feeding.
Although second generation anti-coagulants have been developed, first generation baits are still widely used. Some rat populations have developed resistance to this class of rat poison.
2) Second generation anti-coagulants were introduced to address some of the drawbacks of the first generation options. This class of rat bait is more toxic resulting in death occurring after a single dose rather than several sequential dosages. Because of their greater toxicity, smaller amounts of 2nd generation anti-coagulants are used in baiting the rats; and are particularly effective on rats which have developed resistance to first generations poisons like Warfarin.
Metal phosphides rat baits such as (zinc phosphide) are considered single dose effective and relatively fast acting alternatives to the anti-coagulant baits. Death of the animal occurs within 1-2 days.
The reaction of the phosphide to the acid in the stomach of the rat releases the highly toxic phosphine gas. Zinc phosphide based pellets exude a pungent odor similar to garlic which is attractive to the rats, but which tends to repel other mammals, making it safer for pets and non-target wildlife. Phosphides are not known to accumulate in the tissues of the dead rats, so the incidence of secondary poisoning is diminished.
Vitamin D rat baits specifically vitamin D2 (ergocalciferol) and Vitamin D3 (cholecalciferol), are another form of rodenticides found in rat baits. These two D family vitamins when ingested at toxic levels interfere with the balance between calcium and phosphates, resulting in a condition known as hypercalcemia.
Hypercalcemia kills by increasing absorption of calcium in foods with the end result being a calcification or mineralization of the blood vessels, kidneys, stomach and lungs. This in turn effects the myocardial action of the heart and results in hemorrhage and kidney failure. This class of rat baits need to be ingested only one time and can take anywhere from a couple of days to a week to kill the animal.
Secondary poisoning dangers
Nearly all of the toxic rat baits present a significant danger not only to family pets (and children if they get into the bait) but also to wildlife. Any species that preys upon rodents (owls, hawks) can and are often affected by poison rat baits through the consumption of affected rats. Federally protected species such as the Bald Eagle, the Spotted Owl and San Joaquin are particularly susceptible to population impact from these poisons.While it was claimed that these Vitamin D rodenticides reduced the possibility of secondary poisoning in pets and non-target animals, subsequent study has revealed this not to be the case. Dogs and cats are at particular risk when these rat baits are used; ingestion of a dead rat loaded with this class of rodenticidal bait will cause progressive renal failure in these animals.
If these baits are set out in areas accessible to deer, raccoons and squirrels, these relatively benign animals are prone to be exposed to and ingest these poisonous baits.
Rat bait poisons and the EPA
Due to the many dangers posed by toxic rat baits, the US Environmental Protection Agency (EPA) announced in 2008 that it was placing new restrictions on the sale and use of 10 rodenticidal rat baits. Scheduled to take effect in 2011, the new restrictions include the sale and distribution of the listed baits, minimum package sizes, use site restrictions, and making packaging tamper resistant.
The use of toxic rat baits has been controversial for many years. With the emergence of renewed environmental concerns among the general public, many pest control companies are forgoing the use of poisonous baits altogether and pledging themselves to “green” non-toxic rat control measures only.