The secrets of the cockroach’s ability to thrive in some of the most disgusting places on Earth have been discovered in its DNA.

The American cockroach spread around the world after it was introduced to the US from Africa in the early 16th century. Its population exploded as the insects made themselves at home in the dark and moist corners of houses, restaurants and offices, where toilets and kitchens became their favourite haunts.



To understand how the species, which can grow to 5cm long, came to succeed in such filthy and unsanitary nooks and crannies, Chinese scientists deciphered the entire genetic makeup of the American cockroach, Periplaneta americana. They found that the species has more than 20,000 genes, making its genetic code as large as a human’s.



Amid the sequenced DNA, Shuai Zhan, who worked on the project at the Institute of Plant Physiology and Ecology in Shanghai, spotted unusually large groups of genes that appear to help the American cockroach survive in the unenviable niches it has adapted to.



Writing in the journal Nature Communications, Zhan describes how the cockroach has an expanded set of genes that helps it sense the smells that waft off food, in particular the fermented foods it favours most. Another group of genes comprise the insect’s internal detoxification system, which protects the cockroach should it eat anything toxic. Yet another batch of genes beef up the insect’s immune system, to combat infections from all the germs it encounters. Together they make the cockroaches more resilient in the face of the filth they live in.



Then there are yet more genes that ensure cockroaches reproduce at an impressive rate, while others underpin the ability of cockroach nymphs to regrow any limbs that are broken or nibbled off by predators. By identifying which genes are key to cockroach survival, scientists hope to find ways to better control them.

For all the genes that Zhan and his colleagues found, the group discovered none to support the claim that cockroaches would survive nuclear armageddon, as is often claimed. “I think this is an overstatement and has not been proved,” Zhan said.