快猫短视频

See gallery: 鈥�The unlikely charm of cockroaches鈥�

You don鈥檛 need to be tough to conquer the world鈥檚 kitchens, but you do need one extraordinary ability

ON A midnight foray into my kitchen, I flicked on the light and was confronted with a devil鈥檚 playground. Cockroaches were fornicating on my pots and dancing on the cooker. They were grinding on my floor and scuttling around my fridge.

Disgusted, I reached for the light switch again. The snack I had hoped for was no longer enticing. But then I saw one critter climbing up the wall. I leaned over to take a look. 鈥淗ow have you come to live in my home?鈥� I wondered briefly 鈥� before squishing it with an empty milk carton and going back to bed.

When I moved from Melbourne to Sydney to work for 快猫短视频, I was told only about the fabulous weather and the views over the harbour. No one mentioned the rampant roaches.

But my midnight encounter was just the first of many, and my question would not go away. So I decided to find out more about my unwanted guests and why they have been so successful in colonising our dwellings.

What I have discovered has taken me by surprise. Contrary to popular myth, these critters are not especially tough or radiation resistant. Indeed, they are pretty average as insects go. But in the past year, it has been shown that cockroaches do have one special power after all.

I began my search by heading to the vast collections of the Australian Museum in Sydney. The variety of cockroaches on display there is astonishing 鈥� big ones, small ones, green ones, striped ones, winged ones and wingless ones 鈥� but I soon noticed that they all conformed to the same basic pattern. While some of their cousins have branched out and evolved specialised features 鈥� such as the mantids, with their spiky legs for grabbing prey 鈥� roaches themselves have retained a rather plain body plan with no stings, pincers or other special traits.

It is estimated that only around 40 per cent of cockroach species can fly, for instance, and most are rather inept at it. They cannot fly very far. As for the notion that cockroaches would survive a nuclear apocalypse, think again: they are not especially tough.

A dose as low as 64 grays . Sure, that is 10 times as much as humans can take, but cockroaches do not look so tough compared with the humble fruit fly, which can survive exposure to more than 640 grays, or the parasitoid wasp, Habrobracon, which needs a colossal 1800 grays to kill it.

鈥淭he humble fruit fly can survive far larger doses of radiation than the cockroach鈥�

Continuing my search, I discover that cockroaches thrived long before there were kitchens. They are one of only a handful of insect orders whose fossil record goes back more than 300 million years. Their heyday was during the Carboniferous period, when around 40 per cent of all insects were , prompting some palaeontologists to describe this period as the Age of the Cockroach. Before turning to beetles, it seems that evolution once had an inordinate fondness for cockroaches.

These ancient 鈥渞oachoids鈥� were not that different from modern roaches. Females had a long ovipositor for laying eggs that disappeared around 140 million years ago, but otherwise they all look pretty similar to my kitchen guests.

Nowadays there are nearly 5000 species of cockroach and they live on every continent except Antarctica, finding homes in caves, woodlands and rainforests. Only a handful of species have adapted to living with humans, but it is these that have spread all around the world (see 鈥淩ogues鈥� gallery鈥�). 鈥淭hey give the rest a bad name,鈥� says entomologist Nathan Lo at the University of Sydney. 鈥淲hile I am repulsed by the pests, not all cockroaches are nasty, some are quite beautiful.鈥� Really?

Two of the most infamous pests are the large American cockroach and the smaller German cockroach. Their names are misleading, as it is not clear where they originated, nor when they spread around the world. It is the German variety, I learn, that infests my kitchen.

Which brings me back to my question: why have these critters been so successful? Martyn Robinson, an entomologist at the Australian Museum, thinks it is partly to do with their lack of specialised features. 鈥淐ockroaches have specialised in not specialising,鈥� he says. In particular, most roaches are not fussy eaters. 鈥淩oaches are masters of cannibalism,鈥� Lo says. 鈥淭hey鈥檒l eat everything and they鈥檒l eat each other.鈥�

Sometimes they even eat us. There are of people sleeping in heavily infested buildings or ships being bitten by cockroaches. The varmints seem to have a special liking for calluses and nails, perhaps because they can nibble them without waking their victims. Sailors on some ships reportedly wore gloves while sleeping to protect their fingernails.

鈥淪ome sailors used to wear gloves while sleeping to stop cockroaches eating their fingernails鈥�

There is, however, something else special about cockroaches besides not specialising. When a cockroach is opened up 鈥� or even just squished 鈥� you can see a white mass that fills much of its abdomen. Known as the fat body, this consists of two types of cells: adipocytes, which are filled with fat globules, and mycetocytes, packed with bacteria.

Around and some have mycetocytes similar to those of cockroaches. But the relationship between a cockroach and its resident endosymbiont, called Blattabacterium, is especially close. Kill the bacteria with antibiotics, and the roaches struggle to survive and often die. Kill the cockroaches and Blattabacterium definitely dies. While some insects acquire mutualistic bacteria from the environment, every cockroach hatches with Blattabacterium already inside it. When the eggs are developing, a few bacteria somehow move from the fat body to the ovaries, where they are taken up by every egg.

Last year, Zakee Sabree of the University of Arizona in Tucson compared the genomes of bacterial strains living inside the American and German cockroach. He showed that the two strains diverged at least 140 million years ago 鈥� around the time the fossil record showed that the two cockroach lineages themselves split (). Since they went their separate ways, neither bacterial lineage has changed much.

Lo thinks the relation between the ancestors of cockroaches and of Blattabacterium was so successful there has been no need for the bacterium to change. 鈥淥nce they developed a relationship, bam! They were able to dominate,鈥� says Lo.

Even before Sabree鈥檚 study, Blattabacterium had come to be seen as a defining feature of cockroaches. When it was found inside the Australian termite Mastotermes darwiniensis, it made people wonder whether termites were related to cockroaches. Sure enough, a genetic analysis by Lo in 2000 confirmed that termites are the descendants of a wood-eating cockroach (). 鈥淎t the time it was a little controversial, but now we know the termite is definitely a type of cockroach,鈥� says Lo.

But what does Blattabacterium do? Most mutualistic bacteria in insects provide them with nutrients that they do not get in their diet and cannot make for themselves. The location of the bacteria provides another clue.

Nitrogen is a key component of amino acids, the building blocks of proteins, but animals usually excrete any excess nitrogen in the form of ammonia, urea or uric acid. By contrast, when cockroaches consume more nitrogen than they need, they store the excess in the fat cells of fat bodies, in the form of uric acid crystals. 鈥淓ven when fed really high nitrogen diets, they still don鈥檛 void the excess nitrogen,鈥� Lo says.

So it has long been suspected that Blattabacterium might help cockroaches recycle nitrogen. No one was able to prove it, though, because the bacterium will not grow outside roach cells. But nowadays there is a new way to find out what bacteria do: sequence their genome.

Even that is easier said than done. Just getting a pure sample of Blattabacterium DNA is tough. The cells containing the bacteria are sandwiched between fat cells, making it impossible to manually extract them. Plus, once the cells are collected, the bacteria have to be separated from the organelles inside the cell. Lo and his colleagues finally managed to isolate the bacterial DNA in 2008. Finally, it was time to sequence the genome.

But Sabree beat him to the punch. In 2009, his team published Blattabacterium鈥榮 genome (). The genomic analysis confirmed the bacteria have all the enzymes needed to convert urea and ammonia into all 10 essential amino acids. They can also produce several vitamins.

So the fat bodies not only provide a store of fat that enables many cockroach species to go for more than a month without food, they also allow it to survive on very poor, low-protein diets. 鈥淚t has its own chef and refrigerator on its back,鈥� says Sabree.

The partnership between the cockroaches and their mutualistic bacteria may well have been the key to their success over the past few hundred million years. Despite their dietary superpower, though, only a few cockroach species had all it takes to conquer human habitations. Entomologist David Rentz has counted no fewer than 84 species of cockroaches around his home in the rainforests of northern Queensland. Yet only the German and American roaches actually live and breed in the house.

The species that have switched to living in human homes are not only able to eat just about anything, they are also able to go for long periods with little water. 鈥淪ome other cockroaches come in at night when the lights are off,鈥� Rentz says, 鈥渂ut usually you find them dead on the floor, because they get dehydrated [in the house],鈥� he says.

The bad news is that the invasion of our homes is not over 鈥� there might be roach reinforcements on the way. One cockroach native to Australia, Methana marginalis, has started turning up in houses around the country in the last few years. It鈥檚 unclear whether it has evolved the ability to breed inside houses yet. Having never found nymphs around his house, Rentz suspects not.

Recently, though, I have started spotting more and more of these native critters 鈥� with their light brown stripes 鈥� around my place. Lo thinks they are beautiful and wouldn鈥檛 mind them walking up and down his arm 鈥渦nlike those filthy Americans鈥�.

I have to agree, they are daintier than the American or German pests. But, if I ever catch them fornicating in my kitchen, it鈥檚 the old milk-carton treatment for them too.

When this article was first posted, the lethal radiation doses mentioned for different species were out by several orders of magnitude because of a conversion error during the editing process.

See gallery: 鈥�The unlikely charm of cockroaches鈥�