How do worms move through hard soil, and how far can ants see?

We explore the curious questions that science can answer

If the soil is rich in food, or compact, worms will in effect eat their way to the surface (Getty/iStock)

How do worms penetrate hard soil in summer?

Earthworms are largely crevice burrowers, so they seek cracks in the soil into which they can squeeze. They move through such crevices by peristaltic locomotion, bulges passing backwards along the body acting as temporary points of attachment in propelling the animal forwards. If the soil is rich in food, or compact, they will in effect eat their way along.

In compact soil, much of the material that passes through the worm is deposited as casts on the surface. In less compact soil a large part is deposited underground. During cold or dry weather many species burrow deeply, cease feeding, curl into a ball and wait for warmer or dryer conditions to return.

The walls of worm burrows get compressed as a result of the worms’ movements, and coated with mucus and urine. Also they may be smeared with worm casts. This creates a smooth coating, which may be more comfortable for the worms than the soil alone. Except under extreme conditions, such as a herd of cattle passing by, there is no danger of worms getting crushed.

Do badgers hibernate?

No – they even give birth in January.

Why are my cat's eyes so bright at night?

Nocturnal animals such as cats – and fishes that live in deep water – have a shiny backing to the retina, a layer of cells called the tapetum. Their eyes seem to glow if a light shines into them. The tapetum reflects light back onto the receptors, making vision more effective in low light conditions. In hoofed mammals like deer, the tapetum contains glistening fibres of connective tissue. In cats, it contains shiny crystals of guanine.

Can dolphins kill sharks?

Yes. Sharks don’t have any bones in their bodies but are made up of cartilage, which is very flexible. Dolphins have very strong noses, which they can ram into the shark’s body to cause haemorrhaging. The shark then bleeds internally until it dies.

Why don't you see seagulls in the Mediterranean?

Actually, you do. But the Mediterranean has a lack of fish compared with places such as the North Sea. This means the number of all sea birds is lower. But there is one gull species called the Mediterranean gull, which looks like our black-headed gull, and one called the Audouin’s gull, whose breeding area is confined to the Mediterranean.

 How far can ants see?

There is no simple answer to this question. Some worker ants have well-developed eyes and can leap from branch to branch. Others have greatly reduced vision and some have no eyes at all.

If I crush an ant that is crawling in my kitchen, other ants clear its corpse away. Why? Do they subsequently eat it?

Most social insects have a well-documented behaviour called necrophoresis which involves the recognition and removal from the nest of dead nest-mates and other decomposing materials. Worker ants recognise the corpses by a number of chemical breakdown products: research by EO Wilson, the famous myremecologist (studier of ants), showed that if the “dead ant” chemical is sprayed on a live ant, workers will quickly carry it out of the nest, just as they would a corpse. The live ant then cleans itself off quickly and re-enters the nest – sometimes to be removed a second or third time if it hasn’t cleaned itself properly.