Marta Wolff: The Colombian scientist who fell in love with flies and helped solve several crimes with them.

For seven months—207 days—in 1999, entomologist Marta Wolff conducted an experiment in a remote pasture at the University of Antioquia in Medellín, where she left a metal box with a five-centimeter-diameter hole. Inside was a dead pig. The animal weighed 17.7 kilos and was killed with two gunshot wounds, one to the head and one to the thorax. At that moment, Wolff approached, accompanied by Alejandro Uribe, a biology student. They knew the body would enter a rigid phase, swell, undergo two more stages of decomposition, and end up as a pile of dried remains. They knew that various insects would enter through the hole in the box and devour the carcass. They didn't know, however, with certainty which insect species would appear or in what order. No one in Colombia at that time had the exact information. And so they embarked on their experiment. The first to arrive, after 15 to 30 minutes, are some ants and flies from the Sarcophagidae and Muscidae families, searching for food. Then the parade begins: two days later, another type of fly lays its eggs in the pig's nose and eyes. Seven days later, Calliphoridae larvae emerge from the ears. Then, the smell. A smell like a dark blow that never leaves the researchers' hair and clothes: it's the pressure of gases in the intestine. Also, seven days later, wasps and other predators arrive to eat the fly larvae. After thirteen days, beetles join in, and the smell of putrefaction no longer exists. From day 51 to day 207, the larvae transform into adult flies. The scene of death—which for insects has been food, survival—is over. Only clean bones remain. It is the first forensic entomology study in the country.

Throughout the experiment, Wolff and Uribe collected samples of the species and recorded each event with the same rigor with which the insects performed their work. They then took the samples to the university's Entomology Group laboratory and, together with two other biologists, identified them. In total, there were 2,314 insects, mostly flies whose larvae had begun to breed. Breeding larvae is not easy; it requires appropriate conditions and attention, but Wolff had a goal. The decomposition mechanism of a pig is similar to that of a human, so what happens to the dead body of one happens to the dead body of another, and Wolff wanted to determine what happened after the death of a person in Medellín.

By then, she had been a professor at the Institute of Biology of the University of Antioquia for two years, where, in addition to teaching, she founded the Entomology Group and the Entomology Collection, which is now one of the best curated in the country, with more than a million specimens. At that time, she was already a specialist in flies. Flies: the order Diptera, which, along with butterflies, beetles, and wasps, is the fourth largest group of insects. They are often associated with disease, garbage, insomnia, hives, and buzzing. Wolff does not. And not only because of the nearly 150,000 species that have been described, very few cause any of the above, but because they fascinate him.

She studied them as an undergraduate in Biology at the University of Antioquia. Also, while working at the Departmental Health Department of Antioquia, her curiosity about identifying bite marks based on the type of insect led her to medical entomology, the branch that investigates the links between insects, health, and disease. She continued studying them in her doctorate in Biological Sciences at the University of Granada, Spain, and her thesis was on the vectors of leishmaniasis, the disease transmitted by a tiny fly that hosts a parasite that settles on human skin.

All of this prepared her for a call, also in 1999. It was César Augusto Giraldo, a pathologist, a leading figure in forensic science, and director of the Northwest Regional Office of the Institute of Forensic Medicine. He suggested she work with the larvae that appeared in the corpses arriving at the Institute, which were usually removed with a hose. So it began.

Today, Marta Isabel Wolff Echeverri, 67, is known as a pioneer of forensic entomology in Colombia, a criminalistics tool that uses insects to determine the time elapsed since a person's death.

She's at home on the outskirts of Medellín, where she lives with two dogs her youngest daughter left her when she went to school. It's a house full of plants, with a laboratory she set up to raise forensically important larvae and an LP collection where Pink Floyd and Led Zeppelin have pride of place. She says her work isn't extraordinary—she doesn't discover who the killer is—but that it requires discipline. She has issued nearly 170 reports for Forensic Medicine, but prefers not to give details of the cases, in part to protect the victims and, in part, because she claims that in Colombia forensic entomologists should be able to participate more in investigations. This is the case in other parts of the world where forensic entomology has been practiced for centuries and helps resolve issues such as whether a body was moved from the place where it died, whether it was injected with toxic substances, whether it died behind closed doors or outdoors, in still water or while moving.

Wearing a colorful blouse, short, curly hair, and a flair for words perhaps forged during thirty years as a teacher that will come to an end this July when she retires, Wolff talks about flies: the beautiful, the resilient, the useful, the adorable. And that's what she achieves: making others see them.

Their beauty isn't immediate. The butterfly shows itself, but you have to know how to see the fly. We need magnifying glasses for such small things. They're essential: they recycle, pollinate, and participate in the decomposition of a body. With only two wings, flies are successful organisms and ecologically the most diverse group on the planet. What does a syringe, sharp and hollow inside, look like? A mosquito's beak. Every fly you encounter is incredible. And those colors and that iridescence.

So why do they come out so badly?

In the urban area. Where do people see flies? In the house and in the garbage. They only know the fraction of flies associated with decomposition. No one stares at a flower to see if a fly will arrive, and it turns out that it does; their diversity is enormous. What makes some of them approach rotten meat or rotting fruit? They have a much more specialized olfactory system in their antennae than ours, so they perceive before we do that garbage smells bad, and for them, garbage is a substrate, food for their offspring. We attract them, but we repel them. And yet, in ancient times, they represented power because... what was the first thing to arrive at a corpse, regardless of whether it was beautiful, ugly, young, or old? A fly.

Wolff is German. Who was the first relative to arrive in Colombia?

His name was Raymond Wolff, and he arrived in Titiribí, Antioquia, in 1875. He was a metallurgical engineer and worked in the El Zancudo mines—the flies chase me—he settled down and got married. My grandfather was born in Colombia, then went to Germany to study music, but he came back, married my grandmother, and my father was born. My mother is from Venecia, in southwestern Antioquia, and that's where my three older sisters were born. Later, my father went to work in Pasto, where a brother and I were born. We returned to Medellín and two more children were born. There are seven of us, a lot.

Discipline. I'm very disciplined; I think it's the way to achieve what you want. Be early, submit on time. And in the academic field, rigor. I like things without tyranny because it's not necessary, but clear and well done.

Your second surname, Echeverri, is very Antioquian. What did you inherit from your mother?

A lot, a lot. My mother was an incredibly driven woman. I think she was the greatest influence on all my siblings. Before, my father wasn't as involved in my children's upbringing. My mother took care of everything. She came from a small town, married quickly, and accompanied my father to Pasto and other places. She had to start working quite late.

Her students also describe her as a caring teacher.

I'm very opinionated, to be honest. I'm also a mother of three, and I have kids who come to the lab so young and spend so much time with me. I'm demanding when it comes to learning, but at the same time I tell them to sit comfortably in the stereoscope so they don't get back pain. I make sure they're well-fed on field trips. If we have to sleep in a tent, it doesn't matter, but we should be well-fed and well-slept, and that's how we work because the outings with me are tough.

Were insects talked about in your house?

There were always animals in my house: a dog, a cat, turtles—we even had a fattened vulture in the yard—chickens, pigeons, a chavarrí. No insects, nothing. At school, they didn't teach us about insects, only about large animals. But I experienced the Jacques Cousteau phenomenon. Many of us are biologists thanks to him because they were the first videos that showed us nature, something that seemed so far away. We knew nothing about marine organisms, but we dreamed of getting to know them.

They were a joy I acquired at university. In my entomology course, I did a project with a classmate, Julio Betancur, a well-known botanist who works at the National University. It involved studying a tree and seeing what insects arrived. It was incredible for me. Later, I did my thesis with Professor Gabriel Roldán on aquatic insects. I had to tackle that without many reference collections, but I identified more than 50,000 individuals.

Flight. I think the most wonderful thing in nature is flight, and insects flew before any other organism. I'm amazed that they've been evolving for 400 million years. Can you imagine their capacity for adaptation? That's why insects are everywhere. Some drink blood, others plant fluids, others are capable of piercing a hard fruit. That doesn't come from nothing, but from adaptation.

Some transmit diseases. One of them is the leishmaniasis you studied.

Or dengue, which is transmitted by mosquitoes, but it's because people left water in a vase or a coconut in the yard. I worked with almost all the diseases: malaria, dengue, leishmaniasis, Chagas, and bites you recognize. When I graduated, they needed someone for a project at the School of Medicine on leishmaniasis vectors, so I started working with Iván Darío Vélez Bernal, whom I married and with whom I had my three children. Later, I joined the Antioquia Health Section in the medical entomology laboratory and completed my doctorate in Spain, also on leishmaniasis vectors.

How did you do as a scientist in Spain?

It was wonderful work, lots of fieldwork, lots of collecting. By the time I was doing my doctorate, I already had my first daughter, Valeria. She was born here, but we took her to live there with Iván. Valeria was less than a year old, and I took her to the lab on Saturdays and Sundays because I had no one to care for her. I sat her with a box of crayons while I worked. Back then, they called us "sudacas," but perhaps being white, redheaded, and having that last name protected me, and that's unfair because those are things you don't choose. The only difficulty I had was that they took part of my thesis to give it to someone who had been there longer. And that was done by a man.

One day, I arrived to work with some vines and found a chain with a padlock. Suddenly, he thought that because I was a woman and a foreigner, I was more vulnerable. We still defended ourselves. I filed the appropriate complaints, the man was demoted from his job, and I was able to graduate.

From those years a milestone in his career emerged: larval therapy.

Everything is linked to medical entomology, to understanding that insects are associated with a dynamic of health and disease. When people consume something that has rotted, they get sick. Flies don't. They evolved their digestive systems to feed on rotten meat full of bacteria that are deadly to vertebrates, but their fecal matter is sterile; there isn't a single bacteria. That's why maggot therapy is used. Fly larvae eat the rotting tissue, and because they have a wealth of digestive enzymes, they inject saliva that softens and cleans a human ulcer. It's less painful than a scalpel and much more effective.

When she returned to Colombia, she continued her studies in medical entomology and enrolled at the University of Antioquia. When did you know you wanted to be a professor?

Since I was at the Antioquia Health Department, because many people came with questions. That I'd been bitten by a bug, that I'd seen a little animal like that at home. They'd call, and I liked to answer. In the lab, they'd call me "Marta's line." I'd say, "Describe it for me," "Don't kill it, take it out like this," or "That bite is typical of so-and-so." I've always liked teaching, but it didn't start with students, but with people on the street. Then the university call came.

At the same time, you began a unique investigation in the country. What is forensic entomology?

It's the interaction or use of insects as a tool to find information and resolve situations. There are several lines of research. One is forensic science, where you can use an insect to estimate the post-mortem interval. Another line deals with stored food in which a worm appears, and you determine its origin. And another deals with homes where there are, for example, termites. In forensic entomology, you reconstruct an event to understand what happened, to say, "This came from here."

You work on all three lines, but especially on forensics.

I was just starting out at university with the leishmaniasis mosquitoes. It was around '99 that we started exploring this subject, watching footage on the stereo to identify species.

What did you encounter at the beginning?

In forensic entomology, one works with fly larvae that are collected and bred, but in Colombia, we didn't know which species of flies feed on vertebrate bodies. There wasn't any such work, nor were there any specimens in collections. What was done before? A body infested with larvae was hosed down before performing the necropsy.

Why do flies come to a corpse?

They are the first to arrive at the body of any dead animal, whether it be a person, an orangutan, or a squirrel. Why? As soon as it begins to decompose, the body generates subtle gases that humans don't perceive, but flies, which are always patrolling, pick up the scent in the air. These first flies, which are usually from a very pretty family called Calliphoridae—metallic green, blue, and violet—arrive at the body and seek out the softest regions and cavities so the larvae are protected from other animals and the sun and don't dry out. Our cavities are the nose, the corners of the mouth, the tear ducts, and if the person isn't clothed, the anal region. They immediately lay eggs or deposit larvae. From the egg, a larvae measuring two millimeters emerge, which begin to feed on flesh. A corpse is meat.

And then other bugs appear…

The larvae begin to feed and soften the tissues further so that beetles, for example, can enter. Also, during decomposition, and thanks to the work of flies, salty liquids are released, attracting bees, butterflies, and ants. Many insects come to eat the larvae or feed on the body, and the flies make the body more attractive. They prepare it for others until only skin and bones remain.

So you come in as a forensic entomologist and what do you do?

The first step is to collect the larvae of the pioneer species, that is, the first ones to arrive and ordered by the Medical Examiner's Office. I place part of it on meat in a small, mesh-lined jar and raise them until the adult fly emerges, which I'll use to identify the species. I fix the other part, suspend its growth, and store it in alcohol. These are the ones I'll use to calculate the post-mortem interval. To achieve this, I have to receive information from the necropsy and conduct a number of preliminary studies to relate the morphology of the larva (in alcohol) with that of the adult (raised). I create growth curves based on the larvae I raise, and I know that to reach two millimeters, a species I've already identified took two hours, for five, eight hours, and for twelve, which is the mature larva, 20 hours. So I can go to court and say with evidence—and not because I feel like it—that a larva found in a body was probably five hours, five days, or three weeks old.

So, rather than the time of death, your opinion is about the size of the larva?

I can't say, "They killed him at three in the afternoon," because only the person who did it knows that. But, based on scientific evidence, I can give an estimate of how many hours that larva took to reach a certain size, and then I can extrapolate. That can help a prosecutor resolve the case. It's one more piece in a case.

But the matter gets complicated because the data varies from place to place.

Because it's not just the insect, but the insect and its environment. There are generic ones, but there are species specific to certain environments. There are species specific to Bogotá. What's going on? A body is found in Puerto Berrío, but with a fly from Bogotá. That fly is telling me the body was moved. With the students, we identify the species that arrive at decomposing bodies in different areas of the country. We work from ground zero in dry forest to moorlands like Chingaza.

Your identification of the species in Medellín is pioneering work in Colombian forensic entomology. What was the pig experiment like?

The model for forensic work is the pig because we're very similar in some ways. In a corpse, the first thing to grow are the bacteria that generate gases, which is why the body swells. We have more or less the same bacterial decomposition mechanism with pigs and we share the same intestinal flora. In Medellín, we worked with a pig that weighed almost 18 kilos. We had all the necessary permits. With Forensic Medicine, we got a police officer who shot it, and we immediately began sampling. The idea was to check every day what was happening to the pig, what was coming in. Everything was stored in alcohol to make the babies.

They spent seven months doing that experiment, how could they stand the smell?

I tell the students: "If we were working with roses, it would smell like roses. Since we're working with rotten meat, it smells like rotten meat." It's that simple.

How does a fly detect whether there is poison or drugs in a body?

If there's poisoning or an overdose, this accumulates in a part of the larva called the fat body and in the skin inside. So when the larva molts as it feeds and grows, one can recover the skins and determine what chemical was in the body. This is called entomotoxicology. When the body is so decomposed that blood or urine can no longer be extracted, the insect is there.

Do you remember a forensic case that impacted you?

There was a very difficult one involving a six-year-old girl. I've always enjoyed studying the marks an insect leaves on the skin; that's also forensic entomology. Flies and other organisms reach a corpse, feed on the surface, and leave a lesion similar to a cigarette or acid burn. Then I received the photographs of that girl's case.

They dumped the body in a vacant lot, and ants quickly arrived, biting the skin and leaving red marks. The problem was that they thought the girl had been burned with a cigarette before she died. But it was the ants. At the time, I also had a six-year-old daughter, and I was deeply moved.

And how do you face death?

I had that question at first. I asked Mark Benecke—a German forensic entomologist—and he told me something literal: a dead body has no expression. A corpse is expressionless.

Once you have the report, what next? Do you pass it on to the Forensic Medicine Department, and they pass it on to the Prosecutor's Office?

And are you involved in the rest of the investigation?

Unfortunately, in Colombia, there's no more participation. You go to court to give your opinion, but I don't like it much because of the human aspect. You meet with both families, and both are sad. If I could do it without having to deal with that, I'd continue, but you see the pain, and you're also exposed. I support whoever selects me as a coroner because I think it's important, but the sadness is that everything has become centralized.

I supported the Forensic Medicine Department in Medellín and with them I conducted more than 170 reports. I didn't go to the scene, but they sent me the larvae. We worked like this until the Forensic Medicine Department said no more, they would send everything to Bogotá. There are few people trained in forensic entomology in this country, and on top of that, it became centralized.

What is the situation now?

They don't send samples or they don't collect them anymore. Before, they always collected them, and I constantly received live larvae that I kept in the lab's freezer. So, what a shame, because we've conducted years of research and have a huge reference collection, but we're stuck. We're at a standstill because the Forensic Medicine Department closed that. Why? I don't know.

The insect tool in forensics is enormous, and we're wasting it. Look at mass graves. In the graves, there are flies whose larvae can dig up to two meters deep to find a body. Those larvae could date things, help bring a situation to a close, or help us understand our social history. But they were erased because someone didn't like it, or because it's just plain crazy to work with worms.

At the university, you've taught entomology courses and workshops for prosecutors, police officers, and forensic doctors. Is there a response?

Very good. People want to learn so they can solve problems faster. The difficulty lies in the institutional aspect.

Your work is supported by the Entomological Collection the group has been building. Why is this important?

When I arrived as a professor, I needed tools to work, so I founded the research group, the laboratory, and the collection. It's a heritage collection, and our job is to take care of it. Each insect is a treasure, a piece of evidence, and a window to the past and the future because it warns of what will happen if its environment is altered.

Is there a particularly beloved fly in the collection?

We have a beautiful individual, the Batrachophthalmum quimbaya, which has elongated eyes. It's extremely rare; we only found a male in a forest that had been preserved for over a hundred years in Quindío, where no one had touched it. It has extremely high standards and is saying, 'This is a fragile environment and I am its representative.' We never found it again.

Her colleagues praise her for her persistence, for example, in undertaking the first monumental Catalog of Diptera of Colombia. What was it like?

It was a desire to showcase, to position a group that has been looked down upon due to ignorance. It was a titanic task that allowed us to survey what was in the country and say: "We don't just have beautiful beetles, but also spectacular flies; here's the list." And to encourage people to see that the mosquito isn't just the dengue mosquito and the garbage fly, but that in Colombia we have more than 3,000 species, most of which are native to forests.

Have you suffered from sexism as a female scientist?

I've experienced it, yes, and in my work at the university. Men push us aside, but there are also women who consult a man, even when they know it's another woman who knows the subject. It still happens: they ask a man about mosquitoes or medical entomology with me by my side, because they need a male role model, regardless of whether it's their field or not.

Professor, you announced your retirement, is it official?

Yes, I'm retiring as of July 1st.

Continue working with the group. I set up a lab at home because during the pandemic I had PhD, master's, and undergraduate students. I have the equipment, I put a camera on the stereo, we take photos, and we publish. The idea is to spend more time with my children. When I got divorced, they were very young, and if their father couldn't take them, they would go with me to the lab on Saturdays, Sundays, and vacations. Now they're adults, and we want to be together, but I'm also going to keep producing because I have a lot of pending work.

We're involved in a Belgian-led project called "The Tree of Life." They're working in South America: they're looking for a very old, large, and well-preserved tree in each country, and they're studying everything from the roots to the last leaf. They're also studying insects, birds, fungi, and lichens. In Colombia, they found this tree in Putumayo and invited us to look for flies.

There is also his farm, the second home of the Entomology Group.

Oh yes, it was a wonderful thing that happened in 2003. I got it with some money my mom lent me, and I went with the most wonderful group, the kids from the lab. Every December we have the end-of-year sancocho there. We held a planting festival, and now we have a forest that was declared a Civil Society Nature Reserve. The region is devastated by agriculture, contaminated water, and hunting, but we built a small refuge.

What is the name of the farm, now a reserve?

We called it 'The Fly', for obvious reasons.

Finally, is it true that you are afraid of cockroaches?

Panic! Especially the ones in the houses. And that's even though Colombian cockroach specialist Andrés Vélez trained with us in the group. But yes, how sad, it makes me feel something!