Building a better a rat-trap

They are known to carry at least 70 diseases, including cholera, typhus, bubonic plague and leptospirosis – so not your average household pet. Despite all efforts to reduce their numbers, they far outnumber the human race. In the US, for example, there are believed to be some 300 million humans and one and a quarter of a billion rats. And they cause at least $19 billion worth of damage each year (the rats, that is). Four million rats are born every day and, since they can reach sexual maturity in two months, a single pair can produce 3,500 offspring in a year. A hundred rats will eat about 350kg of grain in a year, while a pair of rats accidentally introduced into a sanctuary for birds, or rare or endangered species on an island, is liable to wipe them out. The Challenge Our challenge this month is to come up with a reliable and effective means of getting rid of rats. The patent literature is full of rat- traps. But, from the abundance of the species, it is evident none has yet been invented that is fully effective. Poisons are liable to kill other species, as well as rats, and rats soon evolve resistance. Even when they do die, they usually choose to do so in some inaccessible location where the smell from their rotting carcases can be perceived for weeks. Cats will kill both rats and mice, but fail to more than dent their overall population. Cats may even assist rat survival by bringing live rats into locations where they can multiply and provide a food supply for the cats. Simple traps are not likely to succeed either. Rats can gnaw through aluminium and lead sheet – never mind wood or plastic – and squeeze through an opening just 12mm across, jump 1m straight up and survive a 6m fall without being injured. They are also resourceful and cunning. What is needed is some kind of mechanical trap that will kill them stone dead, preferably without causing them unnecessary suffering, and leave the expired rats somewhere from where they can easily be removed. The traps should only catch rats, and not other rare and endangered species – and not injure inquisitive children. Electronic control is not an option. Apart from the cost and unreliability, the rat population will quickly learn how to chew through wiring and disable it. The solution offered below solves the problem elegantly and at remarkably low cost, without recourse to any kind of electronics. We won't say it is the perfect solution, but when a very enthusiastic ecologist demonstrated it to us, we thought it the best idea we'd come across so far. The device is very simple, but innovative enough to be protected by patent. For those without access to the web, the solution will be described fully in our November issue. Meanwhile, see if you can come up with a trap for rats that is even 'catchier'. Solution The solution to this month's challenge, comes from New Zealand and is called the Nooski Trap. It uses an expandable rubber ring, which is rolled up a cone and expanded onto a trigger housing. When the rat enters a tunnel and pushes past the trigger, it releases a firing bolt which in turn fires the ring onto the rat's neck/chest area. The rodent springs backwards, dying clear of the trap. The idea of using a rubber ring came from using latex rings for castration, tailing lambs and blood control in the meat industry. This ring, has, however been specially developed for the trap, since it needed to remain expanded with an inside diameter of no less than 40mm and retain up to 90 per cent of its memory despite being left stretched for up to four weeks at a time. The contracting pressure, once released onto the rat, is in excess of 10kg force. Despite this, toddlers suffer no ill effects if they thrust their fingers into the trap and set it off. The makers say , "We are yet to induce tears". The safety tunnel prevents access by larger species. The design has been tested and is endorsed by Landcare Research, New Zealands's leading environmental research organisation.