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Chorus line

Ever since finding a millipede in my bath, I’ve wondered why this creature has so many legs. What advantage do they provide and how did it get them?

• Millipedes and earthworms have similar lifestyles. Both burrow in soil, eating dead and decaying vegetation, but they have evolved very different methods for forcing their way through the soil. Worms use the strong muscles in their body walls to build up pressure in the body cavity, and so develop the forces needed to push forward or widen a crevice in the soil. Millipedes, however, use their legs to push through the soil. The more legs the animal has, the harder it can push.

Millipedes are different from centipedes. They have very large numbers of short legs because Long legs would be a liability in a burrow. Centipedes, which spend their time on the surface or among leaf litter, have fewer, longer legs. They have little need to push, but have to run faster than millipedes.

Millipedes, centipedes and earthworms all have long, slender bodies, divided into large numbers of segments. Except at the two ends of the body, all the segments are built to more or less the same design. Similarly, many products of human engineering are built largely from a series of identical modules. For example, identical seats and windows are repeated many times along the length of a bus. The advantage of this is that one design will serve for all the seats, and one machine can make them all.

In the same way, the repetition of segments in animals reduces the quantity of genetic information needed for development. Millipedes presumably evolved from an ancestor with fewer segments and correspondingly fewer legs, simply by changes in the genes that specify the number of segments.

R. McNeill Alexander

Emeritus professor of zoology

University of Leeds, UK

Jennifer Eccles

Why do some people develop freckles? What causes the freckles to appear, why do they often disappear in adulthood, and why are some people and skin types more susceptible than others?

• Freckles usually appear following exposure to the sun. In order to protect the skin from sun damage, special cells produce a pigment called melanin, which reflects and absorbs harmful ultraviolet rays.

In most people, the distribution of melanin-producing cells is even, creating an all-over, even tan. However, some people have relatively few of these pigment-producing cells and they are not uniformly distributed. A freckle is nothing more than an unusually heavy deposit of melanin at one spot in the skin. People with fair skin – usually people with red or blond hair – not only need greater protection from the sun but are also more likely to develop freckles. Freckles often disappear in adulthood, as the skin builds up all-over protection from the sun after repeated exposure.

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Cutting bills

How do puffins hold a dozen or so floppy sand eels or minnows in their beaks? I see so many photographs of puffins with their apparently sharp, bolt-cutter beaks holding a neat line of fish. If I try picking up fish one at a time, as I presume puffins do, with scissors or even my fingers, I find it impossible. How do they get them all in a neat line and then avoid cutting them in two?

• I think puffins hold their fish with their tongue while catching more of them with their beaks. It would be difficult to hold sand eels with fingers or scissors because fingers and scissors don’t come equipped with a tongue.

Neil Ramsay (aged 11)

Bearsden, Strathclyde, UK

• Puffins can catch more fish when they already have some in their bills because they hold those already caught in place with their tongues. The fish are not severed because they are not gripped by the sharp edges of the bill.

Birds’ tongues are more useful for this purpose than mammals’ because they are stiffer. They are supported by a bony skeleton, and are often adorned with spines and other protuberances that make it easier to grip food. As a result many species share the puffin’s ability to deliver several prey items to the nest in one visit – observe blackbirds on a lawn during the breeding season or tits visiting a nest full of young.

Birds’ stiff yet flexible tongues are used in all sorts of other ways. The tongue is the basis of the pump action that flamingos use to filter-feed. A woodpecker can push its tongue deep into tunnels in trunks to capture a grub. Watch a canary feeding on millet: it uses its mandibles to crack the outer husk, then holds the seed between the edges of its mandibles and rotates it by using its tongue, so that the thick outer husk as well as the inner papery coat on the seed are removed.

J. J. D. Greenwood

Director, British Trust for Ornithology

Thetford, Norfolk, UK

This week’s question

Pretty in pink

I read once that flamingos evolved their bright pink hue as camouflage to hide them from predators against the sunrise and sunset – the times when they feed. Is this true? And, more interestingly, how do they attain their colouring?

Partinger Hammond

Auckland, New Zealand