From the Jha Lab: Using Pollen to Solve Crime

Crime scenes are often the stuff of fascination for many, ripe for the various outputs of fiction. What might be somewhat less glamorous than many TV shows would suggest are some of the crime-solving tools available to forensic investigators. Enter forensic botany and palynology. Forensic botany is the science that connects plants to criminals and/or crimes, and palynology is the study of pollen and spores in a geological or archaeological context.

Researchers in the lab of Dr. Shalene Jha investigate ecological and evolutionary processes and work with pollinators such as bees. Through this, they also are able to assist forensic investigations. Gabriella Pardee is a post-doc in the lab for Dr. Shalene Jha, and is using pollen forensics to track moving organisms and determine biogeographic origins.

Biodiversity Center: Can you explain how pollen would be present at a crime scene and the role of pollinators in this process?

Gabriella Pardee: Pollen is everywhere. It is produced in large quantities by almost every flowering plant on Earth and gets released into the environment through wind and water and is moved around by animals. Each flowering plant species produces pollen grains with a unique and complex morphology, allowing pollen to be traced back to the plant species it came from. Pollen grains are too small to see with the naked eye (most grains are under 200um) and are coated in a sticky substance, which allows grains to easily and inconspicuously attach to many surface types, including rubber, fabrics, hair, fur, metal, and skin. Every time you go outside, you are likely picking up hundreds, if not thousands, of pollen grains on your clothing without even realizing it. These pollen grains can last for many years because they do not decompose due to their hard outer layer. This means that pollen can be perfectly preserved in amber thousands of years after it was released or be used to solve a crime many years after it was committed.

Given these characteristics, pollen can be an important tool in helping investigators determine where a crime occurred and who committed it. For example, since each plant species produces a unique pollen grain, investigators can place a suspect at the scene of the crime by matching the types of pollen found on his/her clothing with the flowering plant species present at the crime scene. Further, if investigators are trying to locate a missing person or object, they can examine the pollen collected from a suspect’s clothing to create a unique location of the likely area where the crime may have occurred.

Since pollinators are reliant on flowering plants for food and nesting resources and collect pollen on their bodies almost every time they visit a flower, pollinators can help us characterize plant communities across the landscape. Further, since pollinators are highly mobile organisms, tracking their movement by swabbing their body for pollen can provide us with a greater understanding of how pollen can be picked up and transported to different locations.

BC: When did people begin to understand that pollen could be used to help forensic investigations?

GP: The first known case of using pollen to aid with forensics investigations was from a crime that occurred over 60 years ago in Austria. A man went missing near Vienna, but the police could not locate his body. Their main suspect in the case would not confess to killing the missing man, so the police decided to bring in a palynologist (a person who studies pollen) to examine the mud on the suspect’s boots. The palynologist found that the pollen of the suspect’s boots contained spruce, willow, and alder pollen, along with 20-million-year-old fossil hickory pollen. This hickory pollen could have only come from one specific area, which contained exposed sediment from the Miocene age. This allowed investigators to home in on a location 20km north of Vienna. When the police brought this evidence to the suspect, he ultimately confessed and led the authorities to the missing man’s body, which was found in the same area that the palynologist identified through the pollen.

Since this first case, pollen has been used in homicide, missing persons, narcotic, and terrorism cases throughout many countries, including the United States.

BC: Are there any disadvantages or difficulties of using this technique?

GP: The biggest disadvantage of using pollen to help solve crimes is the difficulty of identifying pollen species. The main identification technique is through light microscopy where pollen is identified under a microscope using morphological features, such as shape, size, surface structures, and internal details. Though this process sounds pretty straightforward, pollen can be incredibly difficult to get accurate species-level identification because some pollen is visually very similar to other species. Therefore, pollen identification requires someone with a strong knowledge of palynology and taxonomy to be able to see the minute features of pollen. Unfortunately, there aren’t many trained palynologists who can help with pollen forensics, which might explain why pollen forensics isn’t widely used despite its success rate for solving cases.

An alternative identification method that is slowly gaining more traction is using DNA metabarcoding. With this method, a short section of DNA from a specific gene or genes is collected from pollen. This section is then compared with a reference library containing sections of DNA from known plant species to be able to match the pollen with its plant species. While it might be easier to accurately identify pollen using DNA over light microscopy, it is a considerably more expensive method.

BC: How does the Jha lab assist with palynology and/or forensic botany specifically?

GP: The Jha lab is part of a federally-funded Multidisciplinary University Research Initiative (across 5 institutions) that identifies pollen using DNA extraction to better understand pollinator foraging behaviors, pollen/pollinator origin, and pollination. This metabarcoding skillset can not only be used to provide greater resolution to plant-pollinator interactions but it is also applicable to pollen forensics such as tracking movement of organisms to identifying biogeographic origin.

The past summer, Camila Cortina, a graduate student in the Jha lab, and I conducted a study in which we attached sterile patches of fabric to our pant legs and walked through prairies and community gardens throughout the greater Austin area to pick up pollen from the sites. We then swabbed the fabrics for pollen and are using these data to compare the two different identification methods described above to gain more information on how these two techniques differ in their abilities to characterize the pollen community throughout Austin. Further, we collected bees within each of our study sites and will swab them for pollen to build pollen-transport networks to better understand bee foraging behaviors.

BC: How did you become interested in this field?

GP: I actually had no idea that pollen could be used in forensics until I joined the Jha lab last March. Before I joined the lab, my research focused more on bee conservation and plant reproduction. In my previous postdoc position at the University of Minnesota, I become interested in working with pollen when I conducted a study that that examined which plant species bees preferred to visit within tallgrass by swabbing bees for pollen, then identifying the pollen using light microscopy. When I first looked at pollen under a microscope, I was mesmerized by how different the pollen looked, depending on the plant species it came from. This project made me want to learn more about pollen movement and tracking, which is what drew me to the postdoc position in Jha lab. As someone whose favorite book genre is murder mystery and listens to way too many true crime podcasts, I’ve really been enjoying working with the Department of Defense and FBI through the Jha lab to develop better pollen identification techniques so that pollen forensics can become a more widely used method of solving crimes.