When you think of cockroaches, you think of budget European holidays, being grossed out and the fact they're supposedly indestructible.
Of course, they aren't indestructible, but they are bloody tough, and they're getting even tougher, a study has found.
Cockroaches are getting harder to kill with poisons, a study has found. Credit: PA
The study of German cockroaches - the most common species of the insect - found that the creepy crawlies are developing cross-resistance to a number of insecticides.
During a six-month period, researchers were in some cases unable to reduce numbers even when combining several insecticides, with resistance increasing sixfold within one generation.
Purdue University professor, Michael Scharf, said the findings suggested that it is not possible to control cockroaches with chemicals alone.
According to the Daily Mail, he said: "This is a previously unrealised challenge in cockroaches.
"Cockroaches developing resistance to multiple classes of insecticides at once will make controlling these pests almost impossible with chemicals alone."
Would you happily hold one of these guys in your hand? Credit: PA
Researchers used insecticides from different classes and in various combinations, as exterminators often do this in case a cockroach has developed resistance to a particular class.
Roaches were captured and tested in advance to determine the most effective means of treatment, but even with this advantage, researchers found the creatures difficult to kill.
Professor Scharf said: "If you have the ability to test the roaches first and pick and insecticide that has low resistance, that ups the odds. But even then, we had trouble controlling populations."
The researchers found they were generally able to keep population numbers steady, however, with a mixture of only two insecticides, they found the pests were able to thrive and increase in number.
Cockroaches were already notoriously hardy insects. Credit: PA
They also found that when a sample with 10 per cent starting resistance was treated they were also able to increase in number, with those that survived producing even more resistant offspring.
The difficulty in containing population numbers is amplified by the fact that females can have up to 50 offspring during a three-month reproductive cycle.
Professor Scharf said: "We would see resistance increase four or six-fold in just one generation.
"We didn't have a clue that something like that could happen this fast."
So why are these horrible little demons so hard to kill?
One of the main reasons is because they have 20,000 genes - the same as a human. This genetic sequence enables them to combat infections, detoxify food and even regrow limbs.
Anyone else feel like they've got one on their shoulder?
Featured Image Credit: PA