Get to Know the Scientist Studying How Parasitic Flies Stomach Bat Blood

Microbiologist Kelly Speer uses museum specimens to study blood-feeding insects and their mammalian hosts

An orange-colored fly, as seen from above and below
A close-up shot of a bat fly — a specialized parasite that spends most of its life siphoning blood from bats. Kelly Speer, Smithsonian Institution

The animal world is full of blood suckers — everything from ticks and leeches to jawless lamprey fish and vampire bats gulp down the crimson fluid. While blood-feeding itself is rarely lethal to the host, some blood feeders like mosquitoes transmit deadly diseases like malaria as they dine out. This makes it crucial for scientists to understand the blood-feeding behavior of insects.

One of these scientists is Kelly Speer, a microbiologist at the National Museum of Natural History who studies bat flies, a group of highly-specialized parasites that cling to bats and slurp up their blood. Speer, who is also a postdoctoral fellow at the Smithsonian Conservation Biology Institute’s Center for Conservation Genomics, is interested in understanding the community of microorganisms, known as the microbiome, inside of these parasitic flies. These bacteria help bat flies survive on nutrient-poor blood and impact how the flies spread diseases to their bat hosts.

This month’s Meet a SI-entist coincides with World Health Day, so we talked with Speer to learn more about her research and how understanding blood-feeding insects can have potential human health implications.

Smithsonian researcher Kelly Speer, who studies blood-feeding parasites and their mammalian hosts, holding a Jamaican fruit bat. Melissa Ingala, Smithsonian Institution

What about the dietary preferences of blood-feeding flies and other arthropods captures your interests as a researcher?

I'm really interested in how we can use parasites to learn more about their hosts like bats. Many parasites are blood feeding, so it was a natural extension to thinking about how the microbiome facilitates those [blood-feeding] interactions. The more I started to dig into it, the more I realized that the microbiome in blood-feeding insects is necessary for enabling this diet because blood is a pretty nutrient-poor diet. So these blood-feeding arthropods rely on bacteria to provision nutrients that are missing from blood meal.

As you mentioned, much of your work focuses on the microbiome inside of these blood-feeding animals. What information can you glean from the microbes inside of a fly’s gut?

Understanding the interactions between bacteria and blood-feeding flies tells us about this intricate, very specific dietary niche and how they occupy it. One of the things that I'm focusing on are the evolutionary relationships between these microorganisms and their fly host. It’s likely that different bacteria species provide the same function for blood-feeding insects, which reveals what traits are necessary for blood feeding to evolve.

We could potentially start targeting those specific bacteria in arthropod vectors that are harmful to humans. For example, researchers are already leveraging Wolbachia bacteria [a naturally-occuring microbe that reduces a mosquito’s ability to spread viruses] to control the dispersal of malaria by mosquitoes. If we can target certain bacteria that enable them to derive nutrition from blood meal, it could help keep people healthy.

Why are the historic specimens housed at the National Museum of Natural History so vital for your research?

Natural history specimens are essential for this type of research because I'm trying to look at transitions to blood feeding across many different flies. This type of sampling would be nearly impossible to do without a natural history collection. I'm sampling over 200 different flies belonging to around 30 species. And these flies are spread out around the world, so there's no possible way that I could do that sampling on my own.

So having this resource here allows me to study microbiome variation in flies from around the world. Deriving microbiome information from natural history museums is a new, very exciting frontier for the use of these specimens.

In addition to bat flies, Speer also studies other bat parasites like these blood-engorged bat ticks. Kelly Speer, Smithsonian Institution

While bats have become synonymous with spreading pathogens in recent years, your work explores how parasites infect bats in the first place. Do the relationships between parasites and bats have any potential ramifications for human health?

We do know that some bat parasites transmit pathogens to bats. For example, bat flies transmit bat-specific malaria and also a bacterial pathogen that’s related to the bacteria that causes trench fever in humans. The species of bacteria that infects bats and is vectored by bat flies doesn't infect humans, but it's a really interesting model to examine how things like habitat loss or habitat fragmentation impact arthropod-vectored pathogens of wildlife.

Interestingly, the microbiome of insects also plays a role in that. We know from mosquitoes that certain bacteria can prevent malarial parasites from invading the mosquito. I'm interested in seeing how the bat fly microbiome plays a role in how they transmit bat pathogens and if we can use bacteria to control the disease ecology of wildlife pathogens. This could potentially inform and prevent future pathogen spillover events from bats or other wildlife to humans.

Speer using tweezers to pluck a bat fly off a bat’s rear leg. Kelly Speer, Smithsonian Institution

In recent years, we have all become aware of the health hazards that animal diseases pose. In our current, pathogen-conscious climate, what would you like people to know about the importance of often-reviled animals like blood-feeding insects and bats?

While we must be cautious when it comes to the pathogens that spillover from bats to humans, bats are vital for healthy ecosystems because they eat harmful insect pests, spread seeds and pollinate important plants. We are never going to have strong ecosystems without bats. Fortunately, we can learn ways to coexist with them that keep us both safe.

What's really interesting about bats is that even though they can carry multiple pathogens, they rarely show illness. Their immune systems are being studied for this amazing capacity and they may yield valuable pieces of information for human health. And vampire bat saliva is so good at preventing coagulation of blood that we're trying to use it to develop new medicines for people who have blood clots. So, blood feeding is yielding some really interesting things for us.

In terms of blood-feeding arthropods, we need to control those that spread diseases, like malaria-transmitting mosquitoes. But I think we need to approach other blood-feeding insects, the ones that normally creep people out, with a little bit of curiosity. They can teach us about how different species interact, how wildlife communities respond to environmental change and we can use that knowledge to keep people safe and create healthy ecosystems.

This interview has been edited for length and clarity.

Meet a SI-entist: The Smithsonian is so much more than its world-renowned exhibits and artifacts. It is a hub of scientific exploration for hundreds of researchers from around the world. Once a month, we’ll introduce you to a Smithsonian Institution scientist (or SI-entist) and the fascinating work they do behind the scenes at the National Museum of Natural History.

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