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Ant party
THE LAST WORD Where there’s muck On the London Underground, I was struck by the black dust that cakes the tunnels. Much of it must be human skin. What is the annual mass of skin cells shed into the underground system? People make a billion journeys on the tube each year. Are there other factors? And what other material is the dust composed of?
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It found that underground dust is coarser than that found above ground. The lower proportion of tinier particles is good news for passengers because bigger particles tend not to penetrate as deeply into the lungs and are cleared out more efficiently. Skin contributes very little to dust in the London Underground. We each shed about 1.5 grams of skin per day. Journeys by 2.93 million people per day take an average of 44 minutes. If passenger density had been at present levels since 1863, when the network opened, there would be about 7500 tonnes of shed skin. However, spread across the 402-kilometre network, this would equate to a depth of only about 5 millimetres, assuming
n Two-thirds of airborne dust in the London Underground is iron oxide, mainly produced by abrasion between train wheels and the track. Most of the rest is volatile matter, while quartz accounts for 1 or 2 per cent. Quartz is a component of brake dust, so we can assume that the proportion of quartz would have “Skin contributes very been higher in the days before little to dust in the London electric motors were introduced Underground. We shed to decelerate trains. There are about 1.5 grams per day” also traces of metals such as chromium, manganese and copper. that tunnels have an average The amount of airborne dust width of five metres and that increases from dawn, reaching a dead skin has the same density as peak at around midday. Then it water. Crucially, this also assumes remains fairly constant, with fine there are no microbes to feed on dust carried into the system as it is the detritus. sucked in by air currents from the Mike Follows surface. It then settles overnight. Willenhall, West Midlands, UK More details can be found in a 2004 paper by Anthony Seaton To clarify: 44 minutes is about 0.75 and colleagues in Occupational of an hour. 0.75 divided by 24 and Environmental Medicine (hours in the day) and multiplied (DOI: 10.1136/oem.2004.014332). by 1.5 (grams) equals 0.0469 This research was commissioned grams in 44 minutes. Therefore the by London Underground in amount of skin left by 2.93 million response to health-scare stories people is 137,417 grams. Over 149 in the press. years (the length of time the
Questions and answers should be concise. We reserve the right to edit items for clarity and style. Include a daytime telephone number and email address if you have one. Restrict questions to scientific enquiries about everyday phenomena. The writers of published answers will receive a cheque for £25 (or US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted by readers in any medium or format.
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network has been open) this amounts to about 7478 tonnes – Ed
Ant party The waggle dance of bees has been well reported, but how do ants know to gather in large numbers when one of them, presumably, has discovered a tasty morsel in my kitchen? Does it report back to the nest and organise a foraging party?
n Ants forage randomly. On their way back to the nest with food they leave a pheromone trail that other ants will randomly encounter and identify as “pointing” to a food source, according to the concentration of pheromone at each point. The more food, the more pheromone, and the more ants will pick up the trail. It’s a fascinating and simple system they have used for millions of years. Pheromones evaporate over time, preventing areas becoming saturated and confusing. Many studies have modelled ant foraging behaviour; some are impenetrable, but others can make very interesting reading. Ants are generally unwelcome in the house, and the best way to prevent them coming in is to follow a homeward-bound individual to its point of entry and dowse about a square metre around the area with boiling water, followed by a small amount of anti-ant powder. I carried out a comprehensive study of ants while at college and, although insects in general are
fascinating, I think ants are the most interesting of all – especially the way they nod to each other when passing on a route, just like truck drivers do. Tony Holkham Boncath, Pembrokeshire, UK n Ants communicate with one another through pheromone release. The pathfinder forager ant leaves pheromone trails from the spot where the tasty morsel is residing in your kitchen all the way back to the colony – hence it is able to organise a foraging party. Other ants follow the pheromone trails and also reinforce it, but once all the food is consumed, they stop leaving pheromone trails and disappear from your kitchen floor. One in five foragers are pathfinder ants that can detect previously marked pheromone paths for up to 48 hours. It would perhaps be advisable to clean your kitchen daily. By email, no name or address supplied
This week’s question Finger fightback
I got a tiny cut on my finger last night and within half an hour it was warm and it hurt. The following day it was fine but it set me wondering how fast our bodies can detect an infective agent and slam into defensive action. Can anybody answer this? Jana Svoboda Corvallis, Oregon, US
Why are orangutans orange? A new collection: the usual insight, ingenuity and wit – this time with full colour photographs Available from booksellers and at newscientist.com/orangutans
Last words past and present, plus questions, at last-word.com
It found that underground dust is coarser than that found above ground. The lower proportion of tinier particles is good news for passengers because bigger particles tend not to penetrate as deeply into the lungs and are cleared out more efficiently. Skin contributes very little to dust in the London Underground. We each shed about 1.5 grams of skin per day. Journeys by 2.93 million people per day take an average of 44 minutes. If passenger density had been at present levels since 1863, when the network opened, there would be about 7500 tonnes of shed skin. However, spread across the 402-kilometre network, this would equate to a depth of only about 5 millimetres, assuming
n Two-thirds of airborne dust in the London Underground is iron oxide, mainly produced by abrasion between train wheels and the track. Most of the rest is volatile matter, while quartz accounts for 1 or 2 per cent. Quartz is a component of brake dust, so we can assume that the proportion of quartz would have “Skin contributes very been higher in the days before little to dust in the London electric motors were introduced Underground. We shed to decelerate trains. There are about 1.5 grams per day” also traces of metals such as chromium, manganese and copper. that tunnels have an average The amount of airborne dust width of five metres and that increases from dawn, reaching a dead skin has the same density as peak at around midday. Then it water. Crucially, this also assumes remains fairly constant, with fine there are no microbes to feed on dust carried into the system as it is the detritus. sucked in by air currents from the Mike Follows surface. It then settles overnight. Willenhall, West Midlands, UK More details can be found in a 2004 paper by Anthony Seaton To clarify: 44 minutes is about 0.75 and colleagues in Occupational of an hour. 0.75 divided by 24 and Environmental Medicine (hours in the day) and multiplied (DOI: 10.1136/oem.2004.014332). by 1.5 (grams) equals 0.0469 This research was commissioned grams in 44 minutes. Therefore the by London Underground in amount of skin left by 2.93 million response to health-scare stories people is 137,417 grams. Over 149 in the press. years (the length of time the
Questions and answers should be concise. We reserve the right to edit items for clarity and style. Include a daytime telephone number and email address if you have one. Restrict questions to scientific enquiries about everyday phenomena. The writers of published answers will receive a cheque for £25 (or US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted by readers in any medium or format.
New Scientist retains total editorial control over the content of The Last Word. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK, by email to [email protected] or visit www.last-word.com (please include a postal address in order to receive payment for answers). For a list of all unanswered questions send an SAE to LWQlist at the above address.
network has been open) this amounts to about 7478 tonnes – Ed
Ant party The waggle dance of bees has been well reported, but how do ants know to gather in large numbers when one of them, presumably, has discovered a tasty morsel in my kitchen? Does it report back to the nest and organise a foraging party?
n Ants forage randomly. On their way back to the nest with food they leave a pheromone trail that other ants will randomly encounter and identify as “pointing” to a food source, according to the concentration of pheromone at each point. The more food, the more pheromone, and the more ants will pick up the trail. It’s a fascinating and simple system they have used for millions of years. Pheromones evaporate over time, preventing areas becoming saturated and confusing. Many studies have modelled ant foraging behaviour; some are impenetrable, but others can make very interesting reading. Ants are generally unwelcome in the house, and the best way to prevent them coming in is to follow a homeward-bound individual to its point of entry and dowse about a square metre around the area with boiling water, followed by a small amount of anti-ant powder. I carried out a comprehensive study of ants while at college and, although insects in general are
fascinating, I think ants are the most interesting of all – especially the way they nod to each other when passing on a route, just like truck drivers do. Tony Holkham Boncath, Pembrokeshire, UK n Ants communicate with one another through pheromone release. The pathfinder forager ant leaves pheromone trails from the spot where the tasty morsel is residing in your kitchen all the way back to the colony – hence it is able to organise a foraging party. Other ants follow the pheromone trails and also reinforce it, but once all the food is consumed, they stop leaving pheromone trails and disappear from your kitchen floor. One in five foragers are pathfinder ants that can detect previously marked pheromone paths for up to 48 hours. It would perhaps be advisable to clean your kitchen daily. By email, no name or address supplied
This week’s question Finger fightback
I got a tiny cut on my finger last night and within half an hour it was warm and it hurt. The following day it was fine but it set me wondering how fast our bodies can detect an infective agent and slam into defensive action. Can anybody answer this? Jana Svoboda Corvallis, Oregon, US
Why are orangutans orange? A new collection: the usual insight, ingenuity and wit – this time with full colour photographs Available from booksellers and at newscientist.com/orangutans