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I was interested by the article on the relative sizes of living and extinct mammals and reptiles (Â鶹´«Ã½, Science, 13 February). Surely the reason for the small size of marine dinosaurs relative to modern whales lies in their breeding behaviour? An egg-laying dinosaur, like a modern marine turtle, would have to return to land …

I wish to comment on John Emsley's article 'The secret of Bath's methane-fuelled microbes' (Â鶹´«Ã½, Science, 20 February). The bacterium was originally isolated by us and was given to Stephen Lippard and his colleagues by us. To give the distinct impression that the Americans have now 'unlocked' the secret of the mechanism is preposterous. …

L'Abbe Caselli was not 'a French engineer' but an Italian physicist ('Just give me the fax', 13 February). Giovanni Caselli was born in Sienna in 1815 and studied in Florence with the well-known Leopoldo Nobili (1784-1835). In 1836 he became a priest (and later an abbe). From 1856 he worked for many years in France …

Re your item about cockroach sex pheromones (This Week, 20 February). Females are not alone in producing such alluring materials. The male lobster cockroach produces a sex attractant named, by a more imaginative entomologist, seducin. Presumably this is the cockroach equivalent of aftershave. Insect sex attractants are now used for detecting and monitoring several pest …

Instead of beavering away on climate control research to render Mars habitable in the distant future, wouldn't it be better in the long term to accelerate Venus into the position once thought to be occupied by Erehwon? It might sort out its own climate. What I had in mind is deflecting some of the minor …

Jeremy Holden writes (20 February) to ask why mosquitoes buzz, and suggests that natural selection should ensure that the insects evolve to a stealthily silent strain. It seems clear that Holden has never actually been taunted by a mosquito: they are quite impossible to catch, the buzz does not pinpoint the mosquito as might be …

My guess is that not enough time has passed for 'stealthy' mosquitoes to have evolved. Presumably, for most of the thousands of years during which mosquitoes have attacked soft human flesh, the humans did not live in small, confined bedrooms where a noisy insect would be trapped after betraying its presence. But the mosquitoes of …

The bulk of the mosquitoes' diet is the blood of creatures that are in no position to 'jump out of bed and hunt down and kill the mosquito'. So the evolutionary pressure working against the irritating buzz may not be so great. Ornolfur Thorlacius Hamrahlid College Reykjavik, Iceland

Archaeologists dig up dinosaurs ('Diggers at Dinosaur Cove', 13 February) and the Cretaceous is now an era (picture caption, 'It came from outer space', 20 February). Oh dear. Sir will have a hard time teaching correct terminology if his students quote Â鶹´«Ã½ back at him. Anthony Gouldwell Aylestone, Leicester

Can anyone help me? As a teacher I point out to students every year that helium is a non-metal although the ending -ium is usually reserved for metallic elements. Helium was discovered in the Sun by spectroscopy and no one knew if it was metallic or non-metallic, so why was the -ium suffix used and …

I applaud Daniel Clery's article 'Can we stop another Lockerbie?' (27 February), and particularly his comment that passengers do not appreciate a game of Russian roulette. Before Lockerbie the US Federal Aviation Administration ruled that all US airlines must identify all unaccompanied suitcases and physically inspect them. The British took the view that only the …

Those of us in the NASA Search for Extra Terrestrial Intelligence programme who hosted Nigel Henbest's visit a few months ago feel saddened and disappointed by his article 'When will Earthlings see the light?' (Forum, 12 December). The essential problem with optical SETI as compared with microwave SETI is the orders of magnitude greater power …