Wildlife experts are warning that rare species of bumblebee could face extinction if hundreds of thousands of homes are built in the Thames Gateway.
Four rare types of bumblebee live in the Thames Gateway area
Four types of bumblebee which are among the most endangered species in the UK thrive on wild flowers in the area.
"We recognise they are rare and yet they still seem determined to build on these sites," said Ben Darvill of the Bumblebee Conservation Trust.
A government spokeswoman said building would be environmentally sustainable.
The Thames Gateway area, covering east and south-east London, and parts of Kent and Essex, is set for 120,000 new homes by 2016.
The Department for Communities and Local Government (DCLG) said 90% of development would be on previously developed land.
But Professor Ted Benton, of the University of Essex, says in his book Bumblebees that the development will be "catastrophic".
He urges the government to do more to ensure the bumblebees survive.
"As well as being very beautiful insects, they are also incredibly important pollinators of the majority of our wild flowers and a lot of our crops," said Mr Darvill.
"Without bumblebees you are talking about reduced crop yields and sweeping changes to the countryside."
Britain and Ireland have 25 native species of bumblebee, of which three have already become extinct nationally.
Five are listed on the UK biodiversity action plan as endangered species and four more are scheduled for inclusion
A DCLG spokeswoman said: "We need to build new homes for our ageing and growing population.
"If possible, wildlife will be reintroduced to the sites following construction and the relevant habitat checks being carried out."
But environmentalists say if the rare species lose their habitat they cannot be reintroduced at a later date.