Entomologists at an insect collection in country New South Wales have a party trick they like to play.

Visitors are given a pair of 3D glasses and asked to first close one eye and then the other while looking at a tray of small beetles, pinned to the cardboard of a specimen tray.

As if by magic, the beetles change from plain brown to vibrant, sparkling gold and green and then back again, as the viewer wearing the glasses closes each eye in turn.

The explanation, given by Dr Ainsley Seago, technical manager of the New South Wales Department of Primary Industries (DPI) insect collection, is that the beetles are using a tricky system called "a circulatory polarised multi-layer reflector".

"There are number of optical and photonic mechanisms that beetles have evolved that are years ahead of anything humans have created," Dr Seago explained excitedly.

The self-described "bug nerd" is part of the intriguing story of the collection, housed at the Orange Agricultural Institute in central west NSW.

Dr Ainsley Seago and Peter Gillespie at the Department of Primary Industries insect collection, housed at Orange, NSW. ( ABC Central West: Melanie Pearce )

Collection dates to 1890s

The NSW DPI collection, which totals an estimated 650,000 specimens from all over the world, was recently valued at $100 million.

Specimens have been obtained through a range of means: from donations by private collectors to the confiscations of illegal insect importations at Australia's ports and airports.

There are whole drawers full of ticks taken from humans, dogs, cats, rabbits, rats and just about anything else unfortunate enough to have encountered one of the potentially paralysing parasites.

The collection's creepy crawlies are stored in 270 green metal cabinets, housed in a climate-controlled, fire-door-protected room with an overpowering smell of the preservative naphthalene.

This tarantula was confiscated after someone tried to import it as a pet. ( ABC Central West: Melanie Pearce )

The collection is large but also significant because it is one of the oldest in Australia, having been started by the-then Department of Agriculture in the 1890s.

Peter Gillespie, collections curator at the NSW DPI, said then, as now, the key aim of the collection was to help farmers deal with pests and parasites in their crops and livestock.

"Agriculture was the backbone of the country ... but a lot of people didn't know what was here [and] we'd deliberately or inadvertently brought in a number of things that impacted on agricultural production," he said.

Earliest specimens

The earliest specimens in the collection were gathered from all over the state by keen bug collectors on horseback or using Cobb and Co coaches.

One of the most prolific collectors was Walter Wilson Froggatt who travelled to some quite inaccessible places, such as west of Brewarrina in outback NSW.

His legacy lives on in the spidery handwriting on the labels attached to the specimens he collected while the state's chief entomologist for about 40 years from the 1890s.

Mr Gillespie said as well as setting the foundations for the collection, Froggatt was also an early ecological warrior and was one of the only dissenting voices against the introduction of cane toads into Queensland.

This insect collection dates from the 1890s and is one of the oldest in Australia. ( ABC Central West: Melanie Pearce )

Bugs with history and hidden stories

Mr Gillespie said the insects in the collection act as a window to the past; for instance, some come from locations once vegetated but which are now all "steel and concrete".

"All collections are ultimately a biodiversity inventory; they point to a particular species being there at a place in time and collected by someone or other," Mr Gillespie said.

Dr Seago said what fascinated her were the stories behind individual specimens.

"I love pulling out a beetle specimen that was collected say, in North Africa in World War II, and I can kind of guess at the story behind that," Dr Seago said.

"I think who was this hapless soldier out fighting Nazis in the middle of the desert who saw a beetle and thought 'I've got to have that and take it home' and now it's in our collection."

Giant stick insects are part of the collection at the NSW DPI's Orange Agricultural Institute. ( ABC Central West: Melanie Pearce )

Significance of collection today

Insects may not always grab the public's attention, or the research dollar, until it comes to the more aesthetically pleasing specimens, such as the iridescent butterflies.

But that does not deter bug fanciers such as Mr Gillespie and Dr Seago who said even the more common-looking insects were making a big difference economically and scientifically for Australia.

Mr Gillespie said the collection was a biosecurity and agricultural aid because it could be used to identify an insect and determine whether it was found in a particular area.

"We facilitate trade decisions; [for instance if] Australia wants to sell a crop to somewhere in south-east Asia, they want to buy it so long as it's free of diseases X or Y or pest Z," Mr Gillespie said.

Dr Seago agreed that not everyone might be as fascinated by bugs as she was, but many saw the value in collecting and studying them.

"While people might not look at this little brown beetle and say 'wow, that's exciting', they will say 'what's this thing eating my truffles or my lucerne'," she said.

"We have a whole group of growers and industry groups who are very interested in our findings."

Work is currently underway at the NSW DPI to increase the amount of information available to the public via a digital database.