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Rock and hole
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THE LAST WORD Rock and hole While holidaying on the Greek island of Paxos, I came upon a pebble beach where many of the stones had apparently been “engraved” by some type of creature. This example (see photo below) is roughly 50 by 60 millimetres, but the same sort of pattern was also present on much larger stones. What type of creature made these, and how and why? (Continued)
■ In the UK, the chalk of the south coast is under constant attack – not just by the sea and pounding shingle, but also by rock-boring creatures. Several species erode such limestone in this way. One common rock and shell borer is the sponge Cliona, which is prevalent on many of the chalk reefs in the sublittoral (the area immediately below the intertidal zone). On the shore, bivalve molluscs called piddocks produce deep burrows in the rock. And on
We pay £25 for every answer published in New Scientist. To answer a question or ask a new one please email [email protected]. Questions should be scientific enquiries about everyday phenomena, and both questions and answers should be concise. We reserve the right to edit items for clarity and style. Please include a postal address, daytime telephone number and email address. You can also send questions and
the surface of chalk, a tiny polychaete worm, Polydora ciliata, dissolves U-shaped burrows using acid. All of these animals greatly weaken the surface of the chalk and are important contributors to its erosion. The pebble pictured has paired holes, suggesting Polydora activity. These holes are the ends of the organism’s U-shaped burrows (see the central/bottom area of the photo). Gerald Legg Hurstpierpoint, West Sussex, UK
Sky high At any one time, around a million people are flying in aircraft. This is a total mass of about 65,000 tonnes. Does this make us the most successful aerial animal now, or is there some species of insect, bird or bat with a greater airborne biomass?
■ On occasion, some animal swarms weigh far more than the total number of plane passengers in the air at any one time. Locust swarms frequently contain over 10 billion individuals and weigh in excess of 20,000 tonnes. However, the largest locust swarms are much bigger than that. In 1875, a swarm occurred over the American Midwest that was larger than California. It was estimated to contain many trillions of individuals and weigh several million tonnes. Just a year ago, Argentina experienced a swarm the size of the state of Delaware, with a total
answers to The Last Word, New Scientist, 25 Bedford Street, London, WC2E 9ES. New Scientist Ltd retains total editorial control over the published content and reserves all rights to reuse question and answer material that has been submitted by readers in any medium or in any format and at any time in the future. All unanswered questions and previous questions and answers are at newscientist.com/lastword/
weight of several 100,000 tonnes, prolonged periods, they do although it isn’t clear that the tend to change the bacterial entire swarm was ever airborne component of the biofilm, at the same time. typically reducing pathogens, The most populous species which are replaced by bacteria of bird, the red-billed quelea, that have beneficial effects. So has a population estimated at regularly using a mouthwash 1.5 billion. During the autumn migration, as many as 100 million “Antibacterial mouthwash may enhance the of one quelea subspecies may protective properties be in the air at the same time as of the oral biofilm” they move to the Zimbabwean highveld. These bird swarms are often compared to those of with antibacterial action may help locusts, but would only have a lessen dental disease and enhance total mass of approximately the protective properties of the 2000 tonnes. oral biofilm. Stephen Johnson All mouthwashes are intended Eugene, Oregon, US to be spat out after use, meaning their effects are limited to the mouth and throat (if they are gargled). And as with toothpaste, Foul-mouthed it is best to “spit don’t rinse”. response Because of this, some mouthwash Given the importance of the will remain in the mouth and be microbiota in our gut for well-being, is swallowed with saliva and other antibacterial mouthwash a good idea? fluids. However, the amount is typically very small and any ■ There are different types of mouthwash agents tend to be mouthwash, including ones neutralised in the stomach with with antibacterial action, the no ill effects. principal purpose of which is The best method for to reduce bacterial plaque, maintaining oral hygiene is to helping to prevent dental decay brush twice a day for 2 minutes and gum disease. with a fluoridated toothpaste An antibacterial mouthwash is and then use small interdental best swished around the mouth brushes or possibly dental floss on its own, not at the time of to help clean between the teeth. brushing the teeth. If used But using a mouthwash at other appropriately, such mouthwashes times can be a beneficial adjunct will reduce bacterial plaque, but to brushing. they don’t tend to remove the Nairn Wilson bacterial biofilm that coats all Emeritus professor of dentistry the surfaces of the mouth. British Dental Association However, if used over London, UK
THE LAST WORD Rock and hole While holidaying on the Greek island of Paxos, I came upon a pebble beach where many of the stones had apparently been “engraved” by some type of creature. This example (see photo below) is roughly 50 by 60 millimetres, but the same sort of pattern was also present on much larger stones. What type of creature made these, and how and why? (Continued)
■ In the UK, the chalk of the south coast is under constant attack – not just by the sea and pounding shingle, but also by rock-boring creatures. Several species erode such limestone in this way. One common rock and shell borer is the sponge Cliona, which is prevalent on many of the chalk reefs in the sublittoral (the area immediately below the intertidal zone). On the shore, bivalve molluscs called piddocks produce deep burrows in the rock. And on
We pay £25 for every answer published in New Scientist. To answer a question or ask a new one please email [email protected]. Questions should be scientific enquiries about everyday phenomena, and both questions and answers should be concise. We reserve the right to edit items for clarity and style. Please include a postal address, daytime telephone number and email address. You can also send questions and
the surface of chalk, a tiny polychaete worm, Polydora ciliata, dissolves U-shaped burrows using acid. All of these animals greatly weaken the surface of the chalk and are important contributors to its erosion. The pebble pictured has paired holes, suggesting Polydora activity. These holes are the ends of the organism’s U-shaped burrows (see the central/bottom area of the photo). Gerald Legg Hurstpierpoint, West Sussex, UK
Sky high At any one time, around a million people are flying in aircraft. This is a total mass of about 65,000 tonnes. Does this make us the most successful aerial animal now, or is there some species of insect, bird or bat with a greater airborne biomass?
■ On occasion, some animal swarms weigh far more than the total number of plane passengers in the air at any one time. Locust swarms frequently contain over 10 billion individuals and weigh in excess of 20,000 tonnes. However, the largest locust swarms are much bigger than that. In 1875, a swarm occurred over the American Midwest that was larger than California. It was estimated to contain many trillions of individuals and weigh several million tonnes. Just a year ago, Argentina experienced a swarm the size of the state of Delaware, with a total
answers to The Last Word, New Scientist, 25 Bedford Street, London, WC2E 9ES. New Scientist Ltd retains total editorial control over the published content and reserves all rights to reuse question and answer material that has been submitted by readers in any medium or in any format and at any time in the future. All unanswered questions and previous questions and answers are at newscientist.com/lastword/
weight of several 100,000 tonnes, prolonged periods, they do although it isn’t clear that the tend to change the bacterial entire swarm was ever airborne component of the biofilm, at the same time. typically reducing pathogens, The most populous species which are replaced by bacteria of bird, the red-billed quelea, that have beneficial effects. So has a population estimated at regularly using a mouthwash 1.5 billion. During the autumn migration, as many as 100 million “Antibacterial mouthwash may enhance the of one quelea subspecies may protective properties be in the air at the same time as of the oral biofilm” they move to the Zimbabwean highveld. These bird swarms are often compared to those of with antibacterial action may help locusts, but would only have a lessen dental disease and enhance total mass of approximately the protective properties of the 2000 tonnes. oral biofilm. Stephen Johnson All mouthwashes are intended Eugene, Oregon, US to be spat out after use, meaning their effects are limited to the mouth and throat (if they are gargled). And as with toothpaste, Foul-mouthed it is best to “spit don’t rinse”. response Because of this, some mouthwash Given the importance of the will remain in the mouth and be microbiota in our gut for well-being, is swallowed with saliva and other antibacterial mouthwash a good idea? fluids. However, the amount is typically very small and any ■ There are different types of mouthwash agents tend to be mouthwash, including ones neutralised in the stomach with with antibacterial action, the no ill effects. principal purpose of which is The best method for to reduce bacterial plaque, maintaining oral hygiene is to helping to prevent dental decay brush twice a day for 2 minutes and gum disease. with a fluoridated toothpaste An antibacterial mouthwash is and then use small interdental best swished around the mouth brushes or possibly dental floss on its own, not at the time of to help clean between the teeth. brushing the teeth. If used But using a mouthwash at other appropriately, such mouthwashes times can be a beneficial adjunct will reduce bacterial plaque, but to brushing. they don’t tend to remove the Nairn Wilson bacterial biofilm that coats all Emeritus professor of dentistry the surfaces of the mouth. British Dental Association However, if used over London, UK