Londoners are being urged to report sightings of a threatened stag beetle.
Campaigners say London is a hotspot for stag beetles - and is nationally significant for the population it supports.
The London Wildlife Trust said the survey would help them understand where the beetles are flourishing.
They can typically be found hiding among dead wood but seem to be scarcer in north London. The species is declining as parks are cleared of wood.
Traffic, human feet and cats are also driving the decline.
Mathew Frith, deputy chief executive of the trust, said: "These are magnificent and important insects, critical players in the recycling of dead wood into new soil.
"We urgently need an up-to-date estimate of the numbers of stag beetles in London so we can understand where they are flourishing and where they are doing less well.
"With this information, we can help improve conservation measures across London and help protect this fascinating beetle for the future."