Natural history treasures

The State Museum of Natural History Karlsruhe is a popular place.

When we visit, a flock of children gather around a tank holding live freshwater crocodiles. They call out excitedly to their friends to come and look.

Nearby, some French tourists admire a pack of stuffed wolves arranged dramatically around a dead bleeding deer and a man sits quietly sketching a stuffed hare.

There are exhibits of minerals, dinosaurs, geography and the insect world - enough to keep any child, and any adult, occupied for hours.

But although entertainment and science education are part of the function of a natural history museum such as this one, their main purpose is another.

Vast storehouses of scientific specimens

"The biggest number of specimens for research or scientific purposes are locked away in special collection rooms and that is where we are heading at the moment," says biologist and beetle specialist, Alexander Riedel, as he unlocks a heavy door at the back of the museum.

Inside the storage room, enormous rows of metal shelving reach up to the roof.

"In this room are more than 20,000 insect drawers and they contain about three million specimens of insects," says Riedel as he pulls out a drawer filled with ground beetles.

Each beetle is tagged with a label showing who collected it, the date and location of where it was collected, and some even have the altitude and GPS coordinates.

"You may have a hundred specimens and then you do further research and find out it is not one species but maybe two or three and then it is quite useful to have a large number and to see in which localities they occur."

Kept on ice

The beetles displayed here have been dried to preserve them. The method has been used for centuries. But drying specimens makes it difficult to study their internal structures - their muscles and soft tissues.

Another old method involved killing the beetles with a chemical, ethyl acetate - but that degrades DNA.

So the display boxes of the past are getting new neighbors - freezers.

Riedel unlocks another room and proudly gestures at the freezer standing inside.

It's his "treasure box" he says.

It contains most of the specimens he's collected in the past seven years - from when he stopped drying specimens and started collecting them in 100 percent ethanol (pure alcohol) instead.

"It's a bit messy," he laughs. And he's right - it looks completely different from the carefully displayed specimen boxes in the other storage room.

For Riedel and other scientists, though, these specimens, kept at -21 degrees, are much more valuable than their dried cousins because the DNA remains quite stable.

The process preserves the soft tissue extremely well, allowing scientists to X-ray the insides and do microtomography, which creates amazing images of the inside of the body.

"It means you can study the brain of a weevil (which is tiny) just in the same way doctors study the brain," Riedel says.

Karlsruhe also holds a large collection of fungi - but unlike the insects and other animals, the way moulds and fungus are collected and preserved has barely changed in hundreds of years.

Mycologist Markus Scholler unfolds a brown paper envelope from the fungi collection and takes out some dried mushroom dating back to 1904.

He scrapes off some pores, puts them on a glass slide and looks at them under a microscope.

"And they look as they looked 110 years ago, they are in fantastic condition," he says.

Why keep specimens?

It's collections such as these that enable scientists to compare the past with the present.

One famous example is the Chernobyl nuclear accident in Ukraine in 1986. It spread a cloud of radioactivity over parts of Europe, including southern Germany.

After Chernobyl, people were worried that mushrooms, which are known to accumulate heavy metals, might not be safe to eat.

Testing was conducted on several types of mushrooms to determine the concentration of caesium 137 - a radioactive isotope. But what the scientist needed was a comparison with levels before the nuclear accident.

Luckily, explains Scholler, a German university had mushroom samples from the year before the nuclear catastrophe, so scientists had a baseline to compare radioactivity levels.

"This is a good demonstration of how you can document environmental change," Scholler says. "You can look back to 1985 and you can also look back to the 17th century."

Many of the specimens at the State Museum of Natural History Karlsruhe are entered on a public database. Researchers and scientists outside of the museum can make requests to study certain specimens.

In the past, this has included requests to study rodent skulls to see how their teeth are worn down, and requests for Australian weevils for DNA sampling.

Some collections languish and just collect dust over decades - science has its trends and some areas of study fall out of fashion.

But museums shouldn't get rid of unpopular collections, says biologist Albrecht Manegold, who curates the mammal collection in Karlsruhe.

"For example, we have a collection of rotatoria - very small aquatic animals - and there are not many specialists for rotatoria. But it would be [wrong] to throw it away just because there is no scientist at the moment studying rotatoria. Maybe in twenty years time there will be interest," Manegold says.

The same goes for peregrine falcon eggshells. Back in the 1950s, it is possible only few people thought saving bits of peregrine falcon eggshells from the previous century would be of any use - until scientists found a use. A short while later, scientists were able to compare eggshells across a span of time, and through that, show the lethal effects of the chemical insecticide DDT.