If elegance is your thing then consider the ash-black slug. Its nightly forays through the forest in search of fungi are the epitome of grace, a stately glide not only along the woodland floor but up and along the mossy branches of trees.

If size is your thing, then the ash-black slug must get your vote. Britain’s biggest slug is one of the largest land slugs in the world. The ash-black slug can grow up to 30cm (11.8in) in length, although most measure up at a still impressive 10-20cm.

This magnificent gastropod (meaning “belly-foot”) is a keeled slug with a pale-coloured ridge running along its back contrasting with its dark-grey colouration. It has a pale stripe along its foot as well.

Slugs are disliked for devouring gardeners’ lettuces but the ash-black slug is not a garden pest but an ancient woodland dweller. Here it feeds on fungi, algae and lichen and lives for an unusually long time, up to five years.

The ash-black slug’s elegance in motion turns into something stranger when it is mating time.

Ash-black slugs are hermaphrodites, so each individual is male and female at the same time. They can reproduce alone but prefer to find a partner, attracting them with a trail of scented slime as they glide up into the trees.

When they find a partner, the pair perform a twirling dance, eventually suspending themselves with mucus from a branch. A striking pale blue corkscrew-like appendage unfurls from the side of each slug’s head. Each corkscrew is actually its penis, and it is as long as the slug’s body.

The slugs pass a package of sperm to each other, and fertilise it themselves. Eggs are laid in the damp woodland floor and young emerge anytime from autumn to spring.

African savannahs may have their “big five” charismatic beasts but on Dartmoor national park there is a “little five” including the ash-black slug. The wet woodlands on the fringes of Dartmoor are a stronghold for the creature.

Threats include natural ones such as the blue ground beetle, which is Britain’s largest ground beetle. Its 3cm size is tiny compared with the slug but it ferociously attacks the bigger animal.

The ash-black slug is not endangered but unfortunately appears to be in decline, possibly because increased air pollution is reducing the ubiquity of sensitive lichens that are a key part of its diet.

So do different, vote slug.

• Welcome to the Guardian’s UK invertebrate of the year competition. Every day between 2 April and 12 April we’ll be profiling one of the incredible invertebrates that live in and around the UK. Let us know which invertebrates you think we should be including here. And at midnight on Friday 12 April, voting will open to decide which is our favourite invertebrate – for now – with the winner to be announced on Monday 15 April.

Weak government climate policies violate fundamental human rights, the European court of human rights has ruled.

In a landmark decision on one of three major climate cases, the first such rulings by an international court, the ECHR raised judicial pressure on governments to stop filling the atmosphere with gases that make extreme weather more violent.

The court’s top bench ruled that Switzerland had violated rights of a group of older Swiss women to family life, but threw out a French mayor’s case against France and that of a group of young Portuguese people against 32 European countries.

“It feels like a mixed result because two of the cases were inadmissible,” said Corina Heri, a law researcher at the University of Zürich. “But actually it’s a huge success.”

The court, which calls itself “the conscience of Europe”, found that Switzerland had failed to comply with its duties to stop climate change. It also set out a path for organisations to bring further cases on behalf of applicants.

The Swiss verdict opens up all 46 members of the Council of Europe to similar cases in national courts that they are likely to lose.

Joie Chowdhury, an attorney at the Centre for International Environmental Law campaign group, said the judgment left no doubt that the climate crisis was a human rights crisis. “We expect this ruling to influence climate action and climate litigation across Europe and far beyond,” she said.

The facts of the three cases varied widely, but they all hinged on the question of whether government inaction on climate change violated fundamental human rights. Some of the governments argued that the cases should not be admitted, and that climate policy should be the subject of national governments rather than international courts.

The plaintiffs attending the hearing in the court in Strasbourg, some as young as 12, celebrated after a member of a panel of 17 judges read out the verdicts. The climate activist Greta Thunberg joined a gathering outside the court before the hearing to encourage faster action.

The KlimaSeniorinnen, a group of 2,400 older Swiss women, told the court that several of their rights were being violated. Because older women are more likely to die in heatwaves – which have become hotter and more common because of fossil fuels – they argued that Switzerland do its share to stop the planet heating by the Paris agreement target of 1.5C (2.7F) above preindustrial levels.

The court ruled that Swiss authorities had not acted in time to come up with a good enough strategy to cut emissions. It also found the applicants had not had appropriate access to justice in Switzerland.

But it also rejected the cases of four individual applicants who had joined the KlimaSeniorinnen.

“I’m very happy,” said Nicole Barbry, 70, a member of the KlimaSeniorinnen who had come to Strasbourg. “It’s good that they’re finally listening to us.”

The Portuguese children and young people – who because of their age will see greater climate damage than previous generations – argued that climate-fuelled disasters such as wildfires and smoke threatened their right to life and discriminated against them based on their age.

The court did not admit the case, deciding that the applicants could not bring cases against countries other than Portugal and adding that they had not pursued legal avenues in Portugal against the government.

“Their [the Swiss] win is a win for us, too,” said Sofia Oliveira, a 19-year-old applicant in the Portuguese case. “And a win for everyone.”

The French case, brought by the MEP Damien Carême, argued that France’s failure to do enough to stop climate change violated his rights to life and privacy and family life. Carême filed the case when he was the mayor of Grand-Synthe, a coastal town vulnerable to flooding. The court did not admit the case because Carême no longer lives there.

The ECHR rejects about 90% of all applications it receives as inadmissible but fast-tracked the three climate cases to its top bench because of their urgency. It delayed hearings on six more climate cases to get a result on the rulings on Tuesday.

The rulings will influence three other international courts that are examining the role of government climate policy on human rights.

Charlotte Blattner, a researcher at the University of Berne who specialises in climate law, said the court had delivered a bold judgment in favour of a viable future. “The nature and gravity of the threat of climate change – and the urgency to effectively respond to it – require that governments can and will have to be held accountable for their lack of adequate action,” she said.

Opinion on Stoney Middleton is divided. Henry Salt, an animal rights campaigner and friend of Gandhi, relied on the village for his wildflower fix when he lived near Chesterfield. He regularly walked seven miles across the moors to get to Stoney’s dramatic gorge, the nearest limestone within his reach. But it was not, he decided, “one of the pleasantest of Peakland villages”. Though “naturally beautiful”, he wrote, it was also “sadly deformed”.

Knowing something of its rich human history – the highwaymen, thwarted lovers, crystal meth cooks and Hollywood stars – I reckon the village can look after itself. Approaching Middleton Dale, on the other hand, a little to the west, I could appreciate Salt’s perspective. Centuries of quarrying tore chunks from this valley, and blasting out a turnpike in the early 19th century bequeathed the village a busy main road that must annoy those living near it. (In better news, the turnpike’s tollbooth, now a listed building, has been a notable fish and chip shop for the best part of a hundred years.)

Nature has done her best to heal the damage. When the fish and chip shop opened in 1926, the dale’s scars were more obvious. Now they’re cloaked in scrubby woodland, which in early summer is warmly vibrant. This spring, though, after weeks of unseasonable cold, upper branches have remained bare, while trunks have been wreathed in dark ivy, only somewhat lightened by emerging drifts of dog’s mercury – classic ground cover on a limestone woodland floor. Dropping into the dale from above can provoke a chill foreboding as the walls close in.

Today, though, the dale seemed lit up. Rafts of rock cress, having found a toehold in cracks and on ledges on the gorge’s rock faces, were now in blossom, smothering the bulging limestone buttresses with drifts of white flowers. It was so startling that I pulled off the road to marvel at this glorious transformation. The plant’s leaves were freshly green, snag-toothed and narrowing to the stem, the flowers’ cruciform petals arranged around lemon yellow anthers, the whole arrangement filling the void above my head to light the way.