Springwatch's Chris Packham and Kate Humble have visited the Norfolk Broads to see a number of its species, including the swallowtail butterfly.
The population of the butterfly, unique in the UK to East Anglia, is slowly on the up due to the rise in milk parsley in the fenland which they feed upon.
As more reed on the Broads is being cut for thatched housing, it has allowed the species' food source to grow.
"This is the place to come and see them without a doubt," said Chris.
Marsh areas are also now managed specifically for this species to maintain their numbers in the UK.
The swallowtail butterfly is Britain's biggest butterfly with a wingspan of up to 80mm (3.15in), but it is more common on mainland Europe.
These butterflies usually produce two to three broods from April to September.
During their visit to Hickling Broad and Horsey Mere Chris and Kate also spot the great crested grebe and the Polish konik.