Can spiders hear you coming?

How spiders “hear” with their legs Spiders don’t have ears, but that doesn’t mean they can’t hear you coming. With eight eyes in addition to eight legs, the creatures navigate mainly using sight and touch, but they also have a limited auditory ability – provided by sensitive hairs on their legs, which pick up vibrations in solid objects, such as leaves and web silk. Previously, it was assumed that airborne sounds would only be detectable from a few centimetres away; but researchers at Cornell University have discovered – by chance – that some spiders can “hear” sounds from across a room. The team had fitted electrodes to the poppy-seed-sized brains of North American jumping spiders, to record their brain activity in response to visual stimuli. Then, during the experiment, a researcher accidentally caused his chair to squeak – and noticed that this, too, caused their neurons to fire. So the researchers then began clapping while slowly backing away from the spiders – and found they seemed to register the sound from up to five metres away. Further experiments in a controlled chamber revealed the spiders were most sensitive to low-frequency sounds, suggesting that the ability may have evolved as a defence against their main predator, the parasitoid wasp, which emits a low sound with its wingbeats.

“Dark sky” puzzle solved Most people, when they go out at night, take the dark sky, punctuated by twinkling stars, for granted; yet as long ago as the 16th century, astronomers looked up and asked themselves: why, if the universe is static and infinite, isn’t the sky lit bright by its infinite number of stars? This is the Olbers’s paradox – named after the German astronomer Heinrich Olbers – and modern science has come up with some answers: for instance, the universe may actually be finite, but expanding faster and faster, a process that reddens the colour of distant stars. Additionally, there were estimated to be only around one billion trillion stars out there – a lot, of course, but not enough to blanket the sky. Now, however, analysis of images from Nasa’s Hubble Space Telescope – which can see regions of space as far as 13.2 billion light years away – has suggested that there are actually ten times as many stars as this. That is enough to light the sky, says the team at Nottingham University, but it remains dark because much of their light is absorbed by giant hydrogen clouds – which, ironically, is the explanation that Olbers himself came up with in 1823.

An end to infertility? In an extraordinary breakthrough in reproductive biology, scientists have turned mouse skin cells into egg cells in the lab – and, for the first time, used them to breed mice pups. The team, in Japan, says that if they can apply the same technique to humans, it would essentially “cure” infertility, and even pave the way for two men to parent a child without the use of an egg donor. The researchers began by taking cells from mice tails and – using a technique developed in 2007 – coaxed them into becoming pluripotent stem cells that can divide infinitely and have the potential to develop into any tissue. Then, they reprogrammed these as sex cells, following a method developed in 2012. Their breakthrough was in maturing those cells into fertile eggs, without having to implant them back into an ovary. Instead, they took ovarian cells from a mouse, and used these to create an ovary-like environment that tricked the cells into developing into eggs. These were then fertilised and implanted in the wombs of female mice. However, of the 4,048 eggs produced, only eight led to live births. Improving this failure rate is one of the many hurdles that will have to be overcome before the technique can be tested on humans.

Cannabis and bone health Long-term cannabis users break their bones more frequently than non-users, reports The Times. However, it isn’t clear whether this is because the drug weakens people’s skeletons – or simply because when stoned, people tend to fall over more. A team at Edinburgh University compared the fracture rates of heavy users (who’d smoked the drug 5,000 times or more), moderate users, and a control group of cigarette smokers, and found that the heavy users had suffered twice as many fractures as the control group.