This week’s top city stories from around the web celebrate ducks and worms, and think about transformations in Hong Kong and Medellín. We’d love to hear your responses to these stories and any others you’ve read recently, both on Guardian Cities and elsewhere. Share your thoughts in the comments below.

Keep on running

Time magazine this week shared a list of US cities ranked according to “health and community fitness”. And the healthiest, fittest city in the country? For the second year in a row, it is Washington DC, which seems to have scored well due to its “above-average access to public infrastructure”. Other healthy cities include Minneapolis, San Francisco and Portland. But who’s at the bottom of the list? Indianapolis came in last, with Memphis and Oklahoma City close behind.

Hong Kong transformations

How does the creation new public transport infrastructure impact the socio-economic character and local identity of a neighbourhood? Isabella Rossen studied the case of Kennedy Town’s Catchick Street in Hong Kong after a new metro station opened in December 2014. Her piece in Proto City explores the gradual changes that have taken place – turning it from a quiet, largely elderly and working-class area full of light industrial uses to a busier neighbourhood with new shops, bars and restaurants, populated increasingly by expats and young professionals.

“What tended to be social spaces for local Chinese residents are being replaced by commercial spaces for newcomers to the neighbourhood,” explains Rossen, after discussions with residents. The changes are happening alongside the recent demolition of traditional tenement blocks in favour of high-rise towers.

Duck lanes

Now, this is certainly the cutest city-related story of the week. As CityMetric reports, to raise awareness about the need for cyclists and pedestrians to safely share narrow towpaths with each another and surrounding wildlife, the Canal & River Trust has installed temporary “duck lanes” along waterways in London, Birmingham and Manchester.

The campaign has painted segregated lanes on the towpaths, along with an image of a duck and the hashtag #sharethespace. If the pictures are anything to go by, the ducks are taking it very seriously.

Medellín

“Medellín is a city with a story to tell,” explains the BBC’s Peter Day, “and it is not altogether pleasant.” Taking a look back at the city’s history, and discussing its future with its mayor, Aníbal Gaviria, Day explores Medellín’s transformations. These developments – including parks and public transport innovations – have moved the city away from its reputation as the world’s murder capital and towards a place providing inspiration for other global cities, attracting the term “social urbanisation”. (Which, Day adds, “a non wonk might characterise as taking marginalised people seriously”.)

Medellín now looks ahead to another urban improvement scheme, which has proved both costly and contentious: burying its central highway artery.

Worms: helping the planet

Some unexpected good news ... about worms. According to CityLab, a new study has found that worms actually help fight climate change. Apparently, microbes in soil produce 10 times more carbon emissions than humans do – but worms feed on these microbes, thus reducing emissions. CityLab suggests urban dwellers help the creatures combat climate change by “vermicomposting” in their own back gardens. But if that’s too much, some cities in North America – including Toronto, Seattle, San Francisco, and New York – are collecting residents’ organic waste for worm-assisted composting.

What do you think of the duck lanes? Will you start vermicomposting in your back garden? Share your thoughts in the comments below.