Inside the world of preserved animals in jars

Written by Angie Lo (July 2023)

In a wing of the Natural History Museum lie the preserved animal collection rooms: large, industrial-style chambers with jarred specimens lining shelves or stored in cabinets. On the floor are also huge fluid-filled metal tanks, housing more gargantuan animals like swordfish. Oliver “Ollie” Crimmen, one of the collection’s curators, has been managing the collection’s fish sections for fifty years. Even after all that time, though, Ollie still shows a sense of wonder for the specimens around him, eagerly pulling out a starfish from its jar. “[They’re] a sort of frozen time capsule of beautiful things in nature,” he says. “I still find new things I’ve not seen before.”

The preserved animal in the jar is an ever-popular icon of science, appearing countless times in film, illustration, TV, and more. In these depictions, they’re often portrayed as mysterious and sometimes scary—sitting in a dim, empty laboratory, glassy eyes staring eerily through the fluid. But in reality, working with these specimens is unexpectedly wondrous and vibrant—and filled with some pretty cool surprises.

Preserving specimens in fluid lets scientists examine their features in extreme detail, allowing them to discover things they wouldn’t have otherwise—ranging from the animals’ physiology to the diseases which affect them. Many fluid-preserved specimens are stored in huge collections: this has the benefit of providing a “big picture” of specimens that helps researchers understand more about biodiversity, and study specimens in the context of place and time. 

In this way, the collections act like archives, earning them the nickname “libraries of life”. And the Natural History Museum holds one of the most iconic libraries, which boasts 22 million specimens including finds from Darwin himself.

This huge collection is a valued hub for a large stream of visitors. Upstairs near Ollie’s office, two visiting scientists have taken samples from jarred animals, and are observing them intently under microscopes. And it’s not just science researchers who come: one particularly interesting visit, Ollie recounts, was from the swimgear company Speedo, who inspected the hydrodynamic skin of sharks to replicate in an Olympic swimsuit design. There are also artists who use the specimens as inspiration. “We had a lady here who took the giant squid [in the collection] and painted it in squid ink,” says Ollie. The NHM also hosts tours of the collection for interested museum-goers wanting a behind-the-scenes look.

James, one of the other fish curators, explains more about managing the collection. “It has to be constantly monitored,” he says. One thing he especially makes sure of is that the alcohol in the jars, which preserves the specimens, isn’t evaporating out of leaks. Otherwise the animals will start deteriorating: “Occasionally, very rarely, you find this specimen that’s in like three inches of black gunge,” he says. “And so that’s something we need to watch for.”

Then there’s the task of adding new specimens to the ever-growing collection. Sometimes they’re collected by researchers, but they also get donated by members of the public. One of the NHM’s most impressive specimens, a glycerin-preserved blue marlin displayed in the main hall, was found washed up on a beach by a group of walkers out with their dog.

Before parting, James shows one last cool thing: a CT scan of one of the collection’s preserved anglerfish. “[It shows] a huge fish inside the anglerfish’s stomach, and I was able to work out what it was just by looking at the scan.” he says The ability to CT scan preserved specimens is a new development–and James is excited to see what more the future has in store for specimen studies.