Rats and other rodents and pests can make great archivists.
That's because they forage food and build dens, storing fabric, paper, animal bones, plant remains and other materials under floorboards, behind walls and in attics. There, these materials might dry out and remain undisturbed for hundreds of years. By analyzing the materials in these nests, archaeologists like me can learn more about the people who once lived nearby.
I studied a rat nest that was used by generations of rats over several decades and was found under the floorboards in the attic of the historic home at Bartram's Garden in southwest Philadelphia. In 1728, Quaker farmer and naturalist John Bartram began to plant his garden, which is considered the oldest botanic garden in North America. I studied thousands of plants collected by rats and learned how the Bartram family used these plants for food, medicine, trade and study.
Rat nests are common in historic structures, particularly homes like Bartram's that contained kitchens and buildings that were used for food storage. The rat nest was discovered during historic preservation work at the Bartram home in 1977. My analysis indicates that it was formed in the late 18th and early 19th century. The materials are representative of the plants rodents would have been foraging from the Bartram home and garden.
The plants I identified weren't restricted to those sold by the Bartram family. They included crops such as wheat, buckwheat, corn, parsnips and beans grown by the family to feed themselves; herbs such as lemongrass, basil and mint used for medicine; and many wild and weedy plants that were not intentionally grown but were nonetheless collected by the rats. By studying the plants foraged by these rats, I learned not only about the important scientific and commercial plants, but also about the food and medicine the family were eating and using, including imported snacks such as peanuts and Brazil nuts.
I am an archaeobotanist. Over the course of almost three years, I sorted through over 11 pounds (5 kilograms) of material from the rat nest. Archaeologists divide these kinds of samples using geological sieves. Then I used a microscope to sort and identify the plants therein. Archaeobotanists find various parts of plants, including seeds, chaff, fruit pits, nutshells and cobs. The plants I identified ranged in size from whole corncobs to weed seeds smaller than half a millimeter. To identify the species, I used reference manuals and comparative collections.
In the future, I plan to focus on the weedy plants recovered from the rat nest. Data from Bartram's Garden will help me and other scholars better understand the timing and details of this process.