 Well, hello everyone. My name is Chris Shrieve. I'm a laboratory instructor at Duke University and I'm here today to tell you a little bit about forensic entomology. So forensic entomology that we're going to be talking about is used in very different domains of the legal field all the way from civil lawsuits up through homicide investigations. I'm sure many of you were familiar with CSI or bones, all the great crime shows, and there's almost always a bug guy or a bug girl who knows all about the insects and how they relate to estimating time of death. We're going to talk about a few more everyday examples before we get to that exciting stuff at the end. So we'll talk about urban forensic entomology, the concerns things like bed bugs and fleas, and also property damage like termites. We'll also talk about stored product forensic entomology, which deals with grain and other food stores that are contaminated or destroyed by insects. And then last, we'll get to the medical legal side of things, which is things like the homicide investigations and using flesh eating insects to determine time of death. So first up, a quick word on urban forensic entomology. So in city environments or in urban settings, humans constantly come in contact with insects. Some of these insects are horrific pests, things like fleas, bed bugs, lice, and other awful things. So we have a variety of pests and parasites. The CDC estimates millions, up to 12 million school children every year are infected with head lice. So either you or someone you're sitting next to has probably had head lice at some point. And it's not a shameful thing. It's not because you're dirty and you don't shower. It's just because lice are everywhere. They've been evolving with humans for millions of years, and they're going to be around for a while, a lot longer. So we also have bed bugs. A lot of you have probably heard about the recent lawsuits in New York. People suing their landlords because the landlords can't get rid of bed bugs. They're really hard to get rid of. They're tied in the tiniest little places in your mattress, and they come out at night to bite you. Other insects like mosquitoes can spread terrible diseases. We have ticks that carry Lyme disease, and there's West Nile virus and other encephalitis diseases that are carried by mosquitoes. So epidemiologists often use insects to trace the pattern of an emerging disease. In addition to the pests and parasites, we also have your friendly co-inhabitants, insects that just kind of live in the same building. That includes roaches, ants, beetles, and termites, along with silverfish and other delightful things. So termites are especially problematic because they can destroy the wood that makes up the structures that we live in. So it's not just that they're coming into our homes and taking our food. They're actually destroying the home itself. So termite damage costs the U.S. approximately $5 billion every year. Roaches and ants often invade your kitchen or your bathroom, and they can carry disease-causing bacteria, even though the insects themselves aren't sick. Let's go on to stored product for insect entomology. So let's say you have a case of grain, and it's totally contaminated with beetles. You want to know who's responsible for that, because if you're trying to sell that grain and you can't, you're out a lot of money. So contamination can happen at various points, and we'll talk about some of the standard insects that are involved. So as you can see here, the Indian meal moth has a global distribution. It is one of the most widespread and annoying of all insects. They can eat almost anything, as larvae, from grains and flour to herbs, nuts. I had an entire bag of pistachio nuts go completely bad because it had meal moths in it, and they loved it. Unfortunately, it ruined my pistachios. And once the food source is contaminated, these moths are very, very difficult to get rid of. We also have a variety of beetles. The little beetle that you see on the screen is actually only about this big as an adult. So they're very tiny, but they stick out like a sore thumb in a pile of white flour. So if you see a beetle in your flower, just scoop it out and send it on its way. There are also a variety of flies and other caterpillars that eat fresh fruits and vegetables. And we'll talk about those in a second. So the FDA, as part of its job, sets a maximum allowance for insect contamination in a variety of food products. I've listed a few of these here. So you can see in peanuts, in a 100-pound bag, if you have 20 whole insects, that can still pass. If you have 21, it's not okay. So that's 100 pounds of peanuts is actually a lot of peanuts, and 20 insects is not a lot. So I think that's pretty reasonable. Imported black olives, the kind that you get sliced on your pizza. You can have up to 10% of them showing damage from fruit fly maggots before the FDA says you can't use those olives anymore. Mushrooms are even worse. If you see a mushroom out in the woods, you can be guaranteed that it's already covered in various fly larvae. Mushrooms are delicious and flies love them. So you can have up to 20 or more maggots of any size in 100 grams of canned mushrooms. That's not very much. But again, they're not going to hurt you. They're just there. The one that probably upsets you the most is looking at the number of insect bits that can be found in chocolate. But this is all because of the way chocolate is produced. They take a pod, crack it open, and they scoop out the beans, and in order to make chocolate from it, they have to grind them in a press. And that grinding is open, and tons of insects can fall in, and they get ground up. So it's not about finding, say, an entire beetle in your Hershey bar. It's about little teeny, tiny bits and pieces showing up in the cocoa beans. Frozen broccoli. They're little tiny plant-sucking bugs called aphids that show up all the time. And again, none of these things present health hazards. They're not going to poison you or make you sick. They just make you question whether you really want olives on your pizza. All right. Now let's get to the real meat of the story. So we're going to talk about what you normally think of when you think of forensic entomology, which is homicide investigations, cadavers, calculating the post-mortem interval and the time of death. So we can use insects to calculate this because insects have a characteristic development pattern. Some insects, like termites and grasshoppers and cockroaches, hatch as little bitty versions of the adult that they're going to grow into, and they go through a series of molts that result in just larger versions of the same thing. This usually takes weeks or months, sometimes even years, to reach adulthood. Other insects, and these are the ones that are primarily used for forensic entomology, go through what we call complete metamorphosis. They have four different life stages, and when they hatch from the egg, they look nothing like the adult is going to. They're either a larva or a grub or a caterpillar or a maggot. So they go through a series of molts getting bigger at each one until they go through a metamorphic molt, which changes their shape completely, and they pupate. And after that, the pupa turns into an adult, so there are two major transitions in complete metamorphosis. Some species can go through this process in a matter of days, some species it takes weeks, and a few species it can take decades to go through an entire life cycle. So it's really, really variable. Here's an example from a species that I work with at home. I grow these every summer just because it's fun. I've been doing it since I was your age. So you start with eggs, the eggs hatch into small caterpillars, and the smaller caterpillars grow and grow and grow until they're about that big. And then they spin cocoons over winter, and in the spring they come out as these beautiful adults that you can see here. So why do insects have to go through so many stages? Why not just hatch and turn into a bigger adult? What's up with all this molting? So because insects have a hard outer shell, they have to molt to get bigger. The outer shell can only stretch so much, and then they have to make a bigger skin inside of that one. So they fold it up and eventually pop out of the old one and crawl out, and then they can get bigger as they grow. So once a caterpillar, or a larva, or a maggot reaches full size, it knows it's ready to go through metamorphosis, and it will initiate a very different molt. So instead of just becoming a bigger caterpillar, it will turn into something that's becoming the adult. So we can use these stages to calculate time of death, or at least the postmortem interval, and we also have to take into account the factors that affect growth rate. Temperature, food quality, oxygen level, and day length, or the time of year. So in general, the relationship between temperature and development time is that the higher the temperature, the faster the insects develop. Insects are cold-blooded, so their temperature is directly tied to the environment around them. The trade-off, of course, if you grow really quickly, is that maybe you reach adulthood before you got as big as you could have. So adult size tends to be a little smaller if you grow really quickly. The advantage, of course, is that you're already an adult, while everybody else is still munching away as a larva. Food quality also has a major role in determining development time. Think about it. If you're eating nothing but junk food, you're not going to grow big and strong, like your siblings who are eating really good nutritious vegetables and proteins and that kind of thing. So if insects are on really poor quality food, it can actually make them molt in place, so they're not getting bigger, they just keep shedding their skin, and they don't develop. Oxygen levels are also a critical factor in development time. Insects are very, very sensitive to the amount of oxygen around them. This is actually how they know that it's time to molt, because the tracheal system, a rigid network of tubes, is a given size for any instar. And as the larva grows, the tracheal system gets farther and farther apart. So the cells in the middle aren't getting as much oxygen as they need, and that's what triggers a molt. So they can grow a bigger tracheal system and support a larger organism. Many insects are very, very aware of what time of year it is. If you have a three-month development time, you know that you don't really want to start that in, say, October. You want to do it in July or maybe April. So the generational timing is very, very tied to the seasons and the time of year, because that is also linked to temperature and food availability and these kind of things. So knowing the time of year and the location, you can estimate what organisms or what insects should be around at that time and how fast they should be developing. So let's talk about the forensically relevant insects. Flies are very widespread. They're usually the first to find a body because they find it by smell. We also have beetles that are usually late to the party, but they show up and they'll help bury the body and help slow decomposition as they eat and they lay their eggs and raise their families there. We also have ants, which are not a major factor in large bodies, but for smaller bodies like mice and squirrels and rabbits, ants can do a lot of work trimming away parts of the body. So we have a group of flies called flesh flies because they eat flesh. The larvae dig through the rotting flesh and scrape with their jaws to liquefy the flesh in front of them and then absorb it. Because they're tunneling through, it has to stay moist. You can't tunnel through jerky, for example. It's really tough and dry. So the corpse has to stay moist and the maggots have to breathe through their tails. Because think about it, if you're digging a tunnel, the only open airspace is behind you. So these flies actually have spiracles. Their breathing system is in their tail. Here's the other end. Here's the head. You can see those scraping jaws in the front. Great for picking away at the flesh right in front of you and slowly eating your way through. So the name sarcophagus means flesh eating. So the flesh flies are classified in the family sarcophagidae. Another group of flesh eating flies are called the blow flies and they're named in Greek for their brilliant colors. They're usually shiny blue or green and they're named californidae. And they're really beautiful adults despite their kind of gross larval development. So a typical fly life cycle includes an egg stage, three larval instars, a pupa, and an adult. So this can take anywhere from a few days to several months depending on the species. For a lot of fly species, the exact timing has been worked out very precisely. So we can use that to calculate time of death. For example, I've got this wonderful image and this information from the National Institutes of Health. So at 70 degrees, the black blow fly has a very, very predictable life cycle timetable. You can see it takes 23 hours from the time an egg is laid to the time it hatches, 27 hours for that first larval instar, and then it molds to the second instar and then to the third. And notice that the third instar is much, much longer. That's where most of the growth happens. Insect growth is an exponential process, which means you start out small and you get a little bit bigger. But then you can get a little bit bigger and by the third instar, you're growing at an exponentially increasing rate. So you're getting bigger and you're getting bigger faster. So this is where most of the growth takes place. After that, the body size is set. The pupa doesn't grow and the adult doesn't grow. So whatever growth is going to happen has to happen during the larval period. And these times are very precise given a steady temperature. So here's a question for you. Given that we know the exact timing of blow fly development and we can extrapolate from that to give an approximate time of death, why is it only an approximate time of death? Think about it, talk about it with your neighbor for a minute, and then we'll go on. Alright, so what do you think? Really, all we find out by calculating when those first eggs were laid is when the flies found the body. It doesn't really tell us how long the body was there before that. Let's say it was raining for three days and the flies weren't out. We can't take that into account just from the development time. Alright? So let's talk about some other insects that could help us out in those situations. So beetles don't really mind if it's raining. So they'll find a body within a few days and they'll start to dig underneath it to lower the body into the ground. This slows decomposition. Beetles would rather eat flesh than rotten mush. But they'll lay their eggs there and they'll grow entire colonies of beetles. Sometimes dozens or hundreds of beetles on a single body. The beetle that you see right here with the yellow shield on its back. That's very common in North Carolina. If you go in the woods and you find a pile of, say, bear scat or a dead body, you'll often find carrion beetles digging on it or eating it. They're really cute and kind of fun. Other beetles are better at cleaning the dry bits, the hair, the fur and the skin of a desiccated body. These are the domestic or the carpet beetle family. Here you can see in this picture, these beetles are being used to clean the last bits of flesh from a deer skull for use as a museum specimen. We're also going to mention ants just because they're important in recycling little bits and pieces, especially of small bodies. Other insects, spiders, birds, mice, they tend not to go for large bodies like, say, a human, but they could and they can do some significant damage to the body in terms of taking it apart and they carry it back to their nest. So rather than just eating the body at the site, they actually carry it away so that presents an extra challenge for forensic entomologists. So the typical sequence, as we've just discussed, flies are almost always first on the scene. They can smell a dead body within minutes or hours of death and they'll start to lay their eggs and the development cycle starts. Carrying beetles arrive later, usually within a few days, and they start to feed as the body decomposes. Once a body is completely dried out or, say, the exposed bits start to get dry, the carpet beetles will start to dig in and they'll lay their eggs and grow there. So let's talk about a few factors that affect how quickly the insects get there. We've already mentioned weather. If it's raining, insects aren't going to be as active, so it'll take them longer to find the body. Temperature also matters. This time of year, when it's really cold, flies aren't as active, but during the summer, they can find a body really quickly because they're constantly flying around looking for one. The degree of exposure of the body also matters greatly. This is one of the reasons that ancient humans started burying their dead is to slow decomposition and prevent insect activity from destroying the body. Location also matters a lot. If you're in a dry environment, very different insects are going to colonize the body than if you're in a really moist environment or a woodland environment or, say, a swamp or a marsh. They're a completely different set of insects will start colonizing the body, including aquatic beetles and other bugs. So let's talk about an example. Let's say you find a small cadaver in the woods. Say it's a squirrel. Squirrels die, it happens. Sad but true. And you notice lots of medium-sized maggots on it. What would you do to determine exactly when that squirrel died? Discuss it with your classmates, and we'll come back in a second. All right, so who's got ideas? Let's talk about the first thing we need to do. We need to take those maggots and get them to somewhere where we can keep the temperature constant because we know the development time most accurately at a constant temperature. So rather than looking at the fluctuations of day and night, let's bring them inside where we can keep them at a steady temperature. So there's the first thing we need to do. And after that, we just have to wait. And what are we looking for? We're looking for that first maggot to go through metamorphosis, so that first maggot to pupate. We know that at 70 degrees, a larva will pupate eight and a half days after the egg was laid. So we can subtract eight and a half days from the day that first larva pupates. And we can say that's the general guideline. That's about how long this maggot was on this cadaver. So the cadaver must have been there at least eight and a half days. So that gives us a rough time of death. We also have to take into account what the average temperature was for the last eight and a half days, especially the time that we had outside. And there's a fancy calculation called the accumulated degree hours, or accumulated degree days, that can tell you exactly how the temperature has affected development time. So we know, for example, if it's been warmer than 70 degrees, development has gone faster than that. So we know eight and a half days is an overestimate for the time of death. It may be closer to seven or even six. If it's been much cooler than 70 degrees outside, we know that the larva's development was slowed down before we found them. So eight and a half days is an underestimate. They were actually there maybe nine or 10 days ago. So using that calculation, we can come up with a fairly exact date of death. We can't get it down to the hours, but we can at least get it down to a specific day, which can make or break the difference in an investigation. So that's all I have for slides. I hope you've enjoyed this little foray into forensic entomology. If you have any questions, feel free to contact me through your other instructors. I'm happy to answer any questions, and I hope you enjoyed. Thanks.