A range of activities is taking place across the UK to mark International Day for Biological Diversity.
Activities ranging from "walking with wolves" to dragonfly spotting will help people to join the worldwide action on a local level, say organisers.
The event is part of a campaign to highlight the loss of species and ecosystems due to human activity.
It marks the highlight of a collection of events this year, the UN International Year of Biodiversity.
Five race-against-the-clock events, or "BioBlitzes", invite people all over Britain to find and identify as many grasses, mammals, insects, trees and birds as they can in 24 hours.
Older children and adults can learn to identify and record animals through pond-dipping, bug-hunting and bird-watching activities, with storytelling, puppet-shows and wildlife games to entertain the smaller ones.
"It's a fun way of encouraging children to recognise and care for the richness of the environment around them," said Hilary Makin, organiser of the Lepe Country Park BioBlitz in Hampshire
The Grant Museum of Zoology in London invites visitors to explore some of the world's weirdest and most wonderful wildlife, including flying lizards and giant starfish.
Volunteers in Coventry can actively help improve the habitat for the severely threatened water vole, with activities organised by the Warwickshire Wildlife Trust.
An off-road safari over the highlands of Scotland will take visitors off the beaten track for three hours of history, geology and wildlife.
As part of a full schedule of events at the Natural History Museum, a competition is being launched to find a new young Natural History reporter.
The Darwin Prize, open to those aged between seven and 14, "provides an arena for children to talk passionately about biodiversity, a subject that many are already very enthusiastic about", explained Marie Clements from the Museum.
Local wildlife enthusiasts all over the UK can also take part in a week-long "Hide and Seek" survey by The Wildfowl and Wetlands Trust (WWT) to help investigate the importance of wetlands for local species.
The action does not stop when the Sun goes down. People all over the UK are invited to spot bats as they take to the night sky, as part of the International Night of Biological Diversity.
The wide range of activities this weekend is taking place just months before world leaders gather in Nagoya, Japan, to set new targets to tackle the rate of decreasing biodiversity.
The many events and activities will "help people understand how crucial biodiversity is, and to discover the connections between themselves and the world around them", say organisers.