The specimens form part of one of the biggest insect collections in the world - second only to that of the Smithsonian Institution in Washington - and their removal is the most complex ever undertaken in Britain.
Over 18 weeks the museum hopes to ship out its entire collection of insects and spiders to eight locations, seven within the grounds of the museum and one at a warehouse in south London.
Here they will be stored temporarily until a £65.5m building at the museum's home in South Kensington is finished ready for their return in 2008 when many will return to public display.
The collection has a rich history, the oldest specimens dating back 300 years and some being brought back to Britain by such scientific luminaries as Charles Darwin and Alfred Russel Wallace, the 19th-century naturalist who, like Darwin, travelled the world in search of rare creatures.
Professor Nigel Fergusson, a museum entomologist who is helping to co-ordinate the move, said the shipment was a logistical nightmare because many of the specimens were old and delicate. "It's a huge project and an incredible responsibility," he said. "The specimens are unique and extremely fragile."
The collection, which includes spiders, is held in 7,250 museum cabinets, containing more than 140,000 drawers holding some 32,000 individual microscope slides for the smaller items. The largest specimen is a 3ft 6ins-tall hornet's nest from China. The smallest specimen is the barely visible fairy fly with a wingspan of less than 8/1000 of an inch; the largest insect is a moth with a wingspan of almost a foot.
Some one million species of insects have been formally described by science and three-quarters of these are defined as "type specimens" kept by the Natural History Museum, Professor Fergusson said.
"The insect collections form an irreplaceable library of life supporting research on human health, biodiversity, conservation and the environment around the world."
Fourteen million specimens alone form the Lepidoptera collection of moths and butterflies which will be stored in Wandsworth, south London. In addition, the removal men have to shift a library of 75,000 bound volumes and 33,000 scientific drawings.
Pests, humidity and fire threatened the collection in its old building which dates from the 1930s. The new Darwin Centre Phase Two will by contrast be an environmentally controlled "cocoon" seven stories high, Professor Fergusson said.
More than £59.6m has been pledged to build the next phase of the Darwin Centre, with funding coming from the Heritage Lottery Fund, the Wellcome Trust, the Garfield Weston Foundation and GlaxoSmithKline, the drugs company.