Cockroaches and radiation
For many people, the only good cockroach is a dead cockroach! But the little devils are very tough, so tough that a rumour has gone around that they could even survive a nuclear explosion. Dr Karl has been sifting through the rubble.
You've probably heard somebody say that come the End of the World, the only survivors would be the cockroaches. Cockroaches have been around for about 300 million years - so they've outlasted the dinosaurs by about 150 million years. They are very tough little critters. They can survive on cellulose and, in a pinch, each other, and they can even soldier on without a head for a week or two - and they're fiendishly fast as well. They have the reputation for being survivors - living through anything from steaming hot water to nuclear holocaust. But at this stage, our grudging admiration has overcome the facts - cockroaches are only a bit better at surviving radiation than we are, and are well and truly outranked in the nuclear holocaust stakes by many other creatures.
Back in 1919, Dr. W. P. Davey did one of the first tests of insect-radiation survivability when he sprayed the Flour Beetle with small doses of X-rays. He was astonished to find that 60 rads seemed to make the flour beetle live longer. Surprisingly, Dr. J. M. Cork found the same result when he repeated the experiment in 1957. A more typical result (ie, that radiation harmed living creatures) was found by Dr. H. J. Muller in 1927, when he used X-rays to cause mutations in the fruit fly.
But there really wasn't a lot research into the field of Being Able to Survive Radiation until the late 1940s and 1950s. Around this time, three factors had emerged. First, there was the existence of the victims of the two Atom Bombs dropped on Japan, second, there was the start of the Cold War and the nuclear standoff between the Superpowers, and finally, there was the search for peaceful uses for nuclear power. As a result, we discovered that we humans are much more susceptible to radiation than insects, and will die after a dose of some 400 - 1,000 rads. For example, some people as far as 21 kilometres from Ground Zero at Hiroshima received doses of 1,200 rads - and suffered slow and agonising deaths. But insects turned out to be much more radiation resistant. Wood-boring insects and their eggs were able to survive doses of 48,000 to 68,000 rads with no apparent ill effect. In 1959, Drs. Wharton and Wharton found that it took 64,000 rads to kill the fruit fly, and a colossal 180,000 rads to be sure of killing the parasitoid wasp, Habrobracon.
As a result of all this testing, it gradually emerged that the cockroach is, at least in terms of nuclear survivability, a wimp. The two Drs. Wharton had found in 1957 that it took only 1,000 rads to interfere with cockroach fertility. In 1963, Drs. Ross and Cochran found that a dose as low as 6.400 rads would kill 93% of immature German cockroaches - making cockroaches only six to fifteen times tougher than we frail humans. Sure, cockroaches survive radiation better than we do - but they curl up and die at doses than don't even bother other insects.
So how did cockroaches get this reputation? Well, if you want to have a mean radiation-resistant insectoid villain, a cockroach fits the bill better than a fruit fly. Cockroaches would die close to Ground Zero of a smallish 15 kiloton Hiroshima-class nuke - and could certainly not survive the larger megaton-range hydrogen bombs in today's nuclear stockpiles.
At the moment, the real King of Radiation is a foul-smellingreddish bacterium called Deinococcus radiodurans, or Conan the Bacterium by its admiring researchers. It was discovered growing happily in canned meat that had gone bad, even though the meat had been sprayed with radiation to preserve it - a nice example of evolution. This bacterium frolics happily in background levels of 1,500,000 rads of radiation - and seems to be able to survive twice as much again, when frozen. So cockroaches are roughly as vulnerable to nuclear attack as the rest of us - but I don't think that knowing that, makes the cockroach more lovable...
Published 23 February 2006
© 2015 Karl S. Kruszelnicki Pty Ltd