 Hello. Today we're going to move on to part two in our series on establishing the postmortem interval. So in part one we talked about the stages of decomposition and we talked about using pigs as proxies for modeling human decomposition. So today we're going to talk a little bit about forensic entomology and the environmental factors that can contribute to the time since death estimation. So let's take a look. So if you recall we started out by talking about the stages of decomposition and how they can predict PMI. So there's sort of a predictable pattern that we can see in the stages of decomposition and we talked about those. And also we have insect behavior and these correspond with these stages of decomposition. And also environmental factors can influence the postmortem interval. So entomology, this is how you can use insects to help forensic scientists estimate the PMI. Also sometimes called forensic entomology. Either way entomology is the study of insects. So this can be helpful in that species that are present on a body tend to develop in a certain series of stages. So it's a predictable interval of stages and also certain insects are going to colonize a corpse at certain times in the decay process. So as a result we can use this as a prediction. Here we have the basic insect life cycle. So most insects are going to start out, pretty much all insects are going to start out as an egg. And then they're going to develop into a series of larvae and then enter the pupa stage and then finally go into the adult stage. Then the adults will lay the eggs and it all starts over from there. But insect growth is actually going to be influenced by several different factors. So one of them would be temperature. So just like when it's hot outside and kids like to go outside and play, the same basic idea can be applied. Insects are more active when it's warm outside than when it's cold outside. Then food quality. If you have something that's protein rich and it's good for you, just sort of like the difference between junk food and good healthy food, you're going to see insects being more active when they have healthy, good protein rich food. Oxygen levels. So with oxygen levels, just like if you can't breathe, you can't grow. So if an insect is trapped in a bag or trapped in a glass or something like that, you'll see that the insect is not going to live for very long. But if an insect has lots of nice oxygen, then that insect can grow a little bit quicker and it'll be more active on the body. And then the day length or the season. So in the winter time we have shorter days and in the summertime we have longer days. And so we're going to see insects being a little bit more active during the summer months than in the winter months. They're also going to follow a common colonization sequence. So what that means is insects are going to come to a body and start living and breathing and surviving on this body in a certain set sequence. So we start out with flies. Flies are going to be the first thing that we see on a corpse, arriving on a corpse. And that's because they're going to be attracted to the odor's decomposition. They smell these odors and know that they have a protein-rich source that they can allow their eggs to grow and develop on. And so these fly development stages would be the most useful for estimating time since death or the post-worm interval. Then you have carrion beetles which are going to arrive within a few days. And then other beetles, dry beetles, carpet beetles if you will, are going to arrive during the drier stages of decomposition. And they're going to be interested in the dry, crunchy bits of a body. So the hair, they're going to be interested in the skin and the bone. So here we have a picture of a fly. This would be, if you notice, this fly has metallic coloring. So this would be sort of what you might expect to see in a common blow fly. And again, this is going to be attracted to that odor of decomposition and all the rich protein that we can find in a decomposing human body. And again, this fly is going to arrive really quickly after death, so within just a few hours of death. This is the life cycle of the black blow fly. So you can see here at about 70 degrees Fahrenheit, this blow fly will develop into predictable intervals. It will develop into predictable stages. So it goes through three different end stars or life cycle stages. And it's going to happen in about 24 hours or so. We're going to have eggs starting to hatch. It can take up to about 48 hours. And then you can see that through each end star, each stage, it gets a little bit bigger and it develops into a pupa finally. And then that pupa is going to sort of burrow into the earth, burrow into the ground. And then it's going to, over time, you'll see that it hatches into the adult fly. All right, so that's what we would commonly see during this initial decomposition phase. So that's what we're going to see on a body that's only been around for just a few days, only been deceased for just a few days. So these are some of the insects that we can expect to find during this initial insect activity, this initial decomposition. We see this is an adult fly. We have, normally we'll see blow flies or bottle flies at this stage. You can see the eggs. So those are sort of the white, kind of look like small bits of rice. The larvae, or the larvae, which are just a little bit bigger. These are going to be really moist for the most part in the early stages. And they're going, as they develop, they become sort of more tough and they can feed on different aspects of the body. So in the larva stage, in that first instar, they'll start out sort of only staying in a small pocket, a small area. And then later they'll actually be able to get through the skin and move on to different areas of the body. And then the pupa. And so here you can see these are the pupa sort of cases that are left behind after they have turned into the adult fly. So the pupa sort of burrow a little bit into the ground. And then you have that fly that emerges, but the pupa shell is left behind for us to observe. Then we have beetles. And normally we see carrion beetles. And these are going to arrive after just a few days. So the flies aren't necessarily gone yet, but we have other insects that are arriving as well. And they're going to be interested in the body at this stage of decay, the putrefaction stage of decay. So if you all recall, this is when the body fluids are really starting to expel from the corpse. That's when we see lots of odor. And this is when we're starting to see more and more insect activity. These are some of the insects that we might find on the body at this time period. So you can have the flesh fly or the house fly, which is pictured here. We have the flesh fly. We can also have beetles, including the hyster beetle and the rove beetle. Then types of predatory wasps, as you can see here. Then during the next state of decay, we're going to start seeing other types of beetles arriving. So during the stage of decay, if you recall, we have the tissue, the soft tissue, starting to get very hard, sort of leathery. We're starting to see some bone starting to penetrate through the skin and so on and so forth. A little less moisture going on. So we have insects that are drawn to less moist areas coming along. So we have beetles, like those seen here. So these are commonly called carpet beetles because they like things like carpet and cloth. And so they're going to be interested in the hair, the skin, and the bone. Here we see some of the other insects that we might expect on a body in the dry state of decay or decomposition. Flies like the coffin fly, which is pictured here. Mods like the clothes moth. And then cockroaches of varying types. And that concludes part two of our estimating the post-mortem interval series.