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You report bees in Puerto Rico evolving to become less aggressive ( 17 August, p 38 ). I believe a similar process is happening in the UK in response to the varroa mite. When I started keeping bees 15 years ago, these mites were a major problem, with all colonies in danger of dying out …

Many diseases may be caused by the spread of Porphyromonas gingivalis , as Debora MacKenzie reports ( 10 August, p 42 ). This reminded me of Colin Barras describing the recently discovered Candidate Phyla Radiation (CPR) microbes that parasitise the mouth bacterium Actinomyces odontolyticus and help it evade the immune system ( 10 April, p …

Discussing the detection of alien life, Sarah Rugheimer notes Fermi's paradox: where is everybody? Geometry may explain why we seem to be alone in the galaxy ( 31 August, p 42 ). Say the volume of our galaxy is about 10 14 cubic light years. Suppose one billion technological civilisations currently exist in it. On …

Adam Vaughan lists challenges facing the UN Climate Action summit ( 14 September, p 6 ). One hurdle that plans for climate change reduction must overcome is that they often involve cutting things that people find enjoyable or convenient – cars and flights, for example. Humans are very short-termist as a species, as our continuing …

It would be a shame if none of the three books on how the global economy is broken that Joanna Kavenna reviews mentioned the way that Australia dealt with the 2008 financial crisis ( 3 August, p 30 ). The Labor government of the time, headed by Kevin Rudd, recognised that employing trickle-down economics would …

Were scientists worried in the 1970s that we were about to plunge into another full-blown icy spell? Jon Stern thinks not, and you suggest that it would have been better to say only a few were ( Letters , 10 August ). As part of my botany course in the early 1970s, I was taught …

You give figures for road traffic casualties, without distinguishing between those who were in a vehicle and other victims 7 September, p 20 ). You also report a claim that advanced driver assistance systems could have the same kind of effect on fatality rates as the introduction of seat belts. But for whom? Some suggest …

I sometimes joke about being a print addict, and now I see disturbing similarities between my reading habit and the behavioural addictions that Moya Sarner discusses ( 14 September, p 42 ). I look up and find I am somehow still reading at 4 am. I experience a "flow state" and am uneasy if deprived. …

Reading about addictions to behaviours , I realise I have become addicted to writing letters to Â鶹´«Ã½ . I scan each issue, looking for some topic that I can pretend to be an expert in. As your article points out, unpredictable rewards strongly increase the addiction, and you contribute to this by only rarely …

• The earliest of our photos of the Mer de Glace glacier was taken in 1919 ( 21 September, p 8 ). • The United Nations definition of "extreme poverty" is an income of US$1.90 per person per day adjusted to 2011 purchasing power parity ( 7 September, p 46 ). • Flaming hell. Harold …