Bluebell thieves are stripping woodlands of their wild flowers before they have a chance to bloom.
Police were called to a wood in Bourne near Peterborough after passers by saw men digging up bluebell bulbs.
By the time officers arrived they had disappeared, but not before clearing a patch of bulbs.
Ian Butterfield, of English Heritage, said bluebells were restricted to older woodlands and thieves could deprive future generations of the plants.
Cambridgeshire Police said there was often a rise in such thefts at this time of year as unscrupulous traders tried to cash in on the demand for spring flowers.