The silvery slime or mucus secreted by slugs and snails (July, p84) has many more advantages, and sometimes disadvantages, than just helping the molluscs to move around easily.
In the marine world, it has been found that some snails add nutrients – particularly nitrogen – to their slime as a fertiliser that stimulates the growth of the algal spores which get stuck to the mucus, thus enriching the habitat for future grazing.
Slime can also be used for navigation, a prime example being limpets, who use their own mucus trails to find their way back to their home spot on the rocks after feeding. They then seal themselves down with mucus to combat desiccation as the tide recedes. Terrestrial snails can also seal themselves into their shells during hot, dry spells.
The slime also contains some pheromones, therefore allowing others of the same species to find a mate (or an aggregation of others for mass mating, as with sea hares and other sea slugs). The creatures seem to be able to sense which direction the trail has been laid in. Unfortunately, though, carnivorous snails can also follow these trails to find their prey, while others can add toxins to ward off predators or secrete toxic mucus which makes them distasteful.
And it’s not just other molluscs that have to be wary of mucus trails. Some years ago marine scientists from Plymouth noted that barnacle larvae avoided settling on dog whelk trails, a voracious predator of barnacles, or near to some species of limpets which have a habit of bulldozing the settling barnacles from the surface of rocks.
Paul Biggin, Hertford
Further to your question, ‘Can marine animals get the bends?’ (Summer, p82), all marine mammals are freediving, and while carbon dioxide may build up over time, the nitrogen they took with them is all they have as opposed to breathing in scuba diving. Scuba diving and its various forms push nitrogen into the bloodstream, freediving does not. Hence, there’s little chance for ‘the bends’ with freediving. Henry Depew,
The Maltese molar
Your feature on Neanderthals (Summer, p64) is of particular interest to us in Malta. The last Neanderthal to be identified was in 2016, when two leading physical anthropologists, Prof Shara E Bailey and Aida Gomez-Robles, confirmed a molar that was discovered in the Dulam Cave in Malta in 1917 as Neanderthal. This find was unique in that the microanatomical features on this molar suggested a blend of Neanderthal with anatomically modern humans of the Late Palaeolithic. Prof Chris Stringer at London’s Natural History Museum extended the research on the molar and involved Prof Svante Pääbo in the discovery. Pääbo, a Swedish biologist, is one of the founders of palaeogenetics and has worked extensively on the Neanderthal genome. He arranged
for DNA studies of the tooth at the Max Planck Institute for Evolutionary Anthropology in Leipzig, in order to settle the issue of whether humans on Malta had mated with Neanderthals. But at that stage the local archaeological establishment opted to take matters into their own hands, and the outcome is still being awaited. Anton Mifsud, MD, DSc, DCH (Lond)
Your comparison (September, p58) of those who do not believe the official account of (eg) President Kennedy’s assassination with Flat Earthers and neo-Nazis discredits you. In the case of the Kennedy assassination, the United States House Select Committee on Assassinations concluded in 1979 – in contrast to the conclusions of the Warren Commission – that Kennedy was “probably assassinated as a result of a conspiracy,” which seems like an understatement of the blindingly obvious. That the cooperation and silence of what seems likely to have been a large number of conspirators could be achieved lends credibility to other, more recent, alleged cover-ups by the leaders of western democracies. Martin Keating, Falkirk
I read your article celebrating 60 years of NASA (August, p56), and am astonished that you left out one of the most important missions NASA ever undertook: Apollo 8.
The Apollo 8 mission achieved a number of significant firsts – the first manned flight of the Saturn V rocket, the first mission to send humans beyond the pull of Earth’s gravity – and produced the stunning Earthrise photograph taken by astronaut Bill Anders. How could you leave this out? Steve Jones, Bedford
On p22 of our September issue, we said that pancreatic cancer patients who received treatment with CBD lived up to three times longer. This was incorrect as the study involved mice rather than human patients.
Apologies, puzzlers. In our September crossword (p96) there were two clues numbered as 21 down.
Why don’t marine animals get the bends? Because they’re not using scuba gear, says Henry Depew
JFK – there was definitely some kind of conspiracy, argues Martin Keating