What exactly does a person experience after death? Let the bugs tell you.
On January 12, 2001, an unnamed body was found in the wild somewhere in Jiangxi Province.
When the forensic doctors arrived at the scene, they found the scene somewhat unusual.
The body's torso was covered with thatch, but the position above the neck was empty—the killer cut off the dead man's head, leaving only a neat section. Who was the deceased? When was he killed? All these mysteries need to be solved through the mutilated corpse and its surroundings.
Forensics first looked at the tissue on the neck section of the corpse, which was already covered with a large number of maggots, about 1-1.2 cm long, and a large number of maggots were also gathered in the soil below the neck, but pupae and pupae shells had not yet been found.
Can these scalp-tingling critters really play a key role in solving the case?
After reading today's update, you will understand.
(Friendly reminder: there are a lot of insect pictures in today's update, and children's shoes with dense phobias are careful!) ）
As a part of nature, when people are alive, they are in close contact with the surrounding environment all the time, and when life is gone, this skin bag will eventually return to nature.
When death occurs, as long as the body continues to contact the external environment, all kinds of microorganisms and various insects will appear on the corpse, which not only helps the corpse to accelerate its return to nature, but also plays a role in helping to infer the time of death in the process of solving the case.
Friends who are familiar with Xiao Zhan and Lao Qin know that forensic doctors can usually judge the time of death by corpse spots, corpse zombies, corpse temperature and other corpse surface conditions. But these methods apply only when the corpse has not yet experienced serious corruption.
When the time of death of the deceased is too long and the physical surface corruption cannot assist in the judgment, the difficulty of forensic doctors to confirm the time of death will be greatly increased, and the insects will come in handy.
In order to accurately infer the time of death, forensic entomologists not only need to accurately identify various insects, but also need to be familiar with their habits, growth and development laws, such as when they will arrive at the corpse and when they will leave. This requires forensic doctors to know the succession of insect fauna on corpses.
This is not an easy task, because the type, number, residence time, etc. of insects on the corpse are also closely related to the environment, climate, species population, and even the cause of death of the deceased.
Although the insect fauna on the corpse varies greatly due to the interference of various factors, it is certain that it still follows a certain law, which is the driving force for forensic doctors to tirelessly study "forensic entomology".
So, how exactly does forensic entomology work?
Below, we will take you into a virtual body dumping site to see what kind of natural "visitors" will be ushered in the corpse over time when it is abandoned on the hot wild grass?
Okay, the wild grass where the bodies were thrown has been selected.
Figure 1 Source: Screenshot of the movie "Little Forest"
Nature has also secretly brewed, and when the anger completely disappears from this human body, the body is about to enter the following five stages:
Stage 1 Freshness
What is changing the body?
The freshness period is the period when the body dies and when the body is mildly decayed and emits a slight smell of decay, but the body has not yet begun to swell.
During this time, corpse spots and zombies will begin to appear within 1-3 hours. The body begins to stiffen, and then the autolysis of the organs begins to occur. At the same time, bacteria in the digestive system begin to multiply and erode the various organs in a certain order, and the first signs of decay are in the blind part of the right lower abdomen of the human body, where the naked eye will appear corpse green.
What are the visiting insects busy with?
During this time, the first to reach the body is the fly we know, and it can arrive within a few hours at the latest.
(Note: The flies we are familiar with belong to the taxonomic suborder Diptera annulatinaceae, which are subdivided into several families, such as Lisa, Hemp flies, Fruit flies, flies, flies, cheeseflies, and so on.) ）
Figure 2 shows the mercerized green fly and its eggs, is it very common? Source: Reference 2
Under ideal conditions (there are plenty of flies near the carcass), the silky green flies of the genus Dipteropterae would even arrive at the corpse within minutes (i.e., almost when the deceased had just stopped breathing) and begin laying eggs on the carcass (due to its rapid arrival, it is important for forensics to push back the time of death based on the development of such flies), and in the next few hours other flies of the family Lizydae also began to appear and lay eggs.
Slightly later than the Lycopodidae, the Hemp-Fly family also arrived very quickly (miraculously, most species of the Hemp-Flies were oviparous).
Figure 3 shows the fly Image source: Reference 6
Of course, there are more than these two families of flies that appear on corpses, but the lilies and the family Hemp flies are the most common in corpses, which is of great significance for inferring the time of death. Of course, there are other insects that appeared during this period, and I will not list them all here.
Tips: Insect sex can be determined by the spacing between the two compound eyes of adults, many species of female flies with a larger forehead width than the male flies. As shown in Figure 4:
Fig. 4 Thick ring-toothed femoral fly, female on the left and male on the right Source: Reference 6
Phase II · Swelling phase
During this period, the corpse continued to decay, the decay gas increased significantly, the whole body began to swell, the rotten vein network gradually became obvious, and the smell of decay was stronger. The well-known "giant view" appeared in this period.
Fly (Diptera) species flourished, while large numbers of beetles appeared carrying mites.
During this period, maggots (fly larvae) continue to develop, reaching their peak in numbers, and the number of adult fly worms also reaches a peak, so you will see countless spectacular scenes of flies dancing around.
Figure 5 shows maggots of different insect ages Source: Reference 1
At the same time, attracted by the smell of decay, there are also a large number of various beetles of Coleoptera (in fact, in the fresh period of the carcass, when the flies begin to lay eggs, adult beetles that feed on maggots and eggs have begun to appear), they feed on maggots or carrion and lay eggs on the carrion, and the beetle larvae also feed on maggots or carrion (some species of beetles only eat carrion, some only prey on maggots and fly eggs, and some have both).
For example, Yan Jia. Insects of the family Yanjia family mostly have the habit of lying down at night, often hiding under corpses during the day, and coming out at night, adults and larvae feed maggots and pupae.
Figure 6 shows several kinds of Yan Jia (inexplicably think a little cute what is going on... Source: Reference 5
Another example is the burial armor. The name fuseric beetle derives from a special habit of insects of the family Funeraceae: they like to dig up the soil beneath the carcasses of small animals, thus burying the corpses in the soil. They lay their eggs on cadavers, some species of funerary couples work together to protect and feed their offspring, adults feed on carrion, fly eggs and maggots, and larvae feed on fluids regurgitated by their parents.
Figure 7 shows several kinds of burial armor (true and beautiful and indispensable) Source: Reference 2 and Reference 5
Interestingly, burial armor also brings mites. Mites have no wings and usually rely on hitchhiking with beetles and flies to reach the corpse. Mites prey on fly eggs, if the burial nails bring enough mites, many fly eggs will not be able to hatch, so the burial shells can enjoy more carrion, mites and burial shell populations will reproduce better, the two cooperate very happily.
Figure 8 shows a burial armor hitchhiked by several mites (the small bugs on the back of the burial armor are mites) Source: Reference 1
A large number of beetles and mites on the eggs of the fly will delay the colonization time of flies (diptera insects), if the forensic doctor who investigates such a scene, only focus on relying on the law of fly succession to speculate on the time of death, it is easy to make mistakes, generally also need to pay attention to the species and number of other insects, in order to finally get a relatively accurate inference.
The third stage is the decay period
The decaying gas continues to be produced until it is excreted through the holes of the anus and maggot bites, the body is no longer swollen and completely integrated into the environment, and its decay process begins to accelerate, and the smell of decay is strong.
Fly larvae and beetle larvae will complete the succession here. Other non-scavenger insects began to appear, and competition among predators became increasingly fierce.
In the early stages of decay, adult fly-like insects flew away one after another, occupying the corpses of maggots that were raised white and fat, and the number of beetles and their larvae also reached a peak.
At this time, maggots will gather together to form maggot clusters, and there will be a spectacular scene of "countless maggots rolling" on the corpse. And if you take a thermometer to measure the temperature inside the maggot mass, you will find that the inside is several degrees higher than the outside.
Figure 11 (Roll It Over!) Maggots Source: Reference 2)
(It is speculated that the formation of "maggots" and the reasons for the high temperature of the center are as follows: maggots feed, constantly exercise and aerobic metabolism will continue to produce heat, and the way they are gathered together can preserve more calories, which is more conducive to the growth and development of larvae.) It is also a synergistic collaboration so that maggots can more efficiently eliminate carrion and develop faster. Ps: Too high temperatures can cause damage, inhibit development, and even lead to individual death, so it is speculated that the emergence of the phenomenon of "maggot rolling" is that they are constantly entering and leaving the gathering area to achieve the purpose of regulating body temperature. At this time, the coleoptera beetle (dù) also began to appear, feeding mainly on the skin, muscles and bones of corpses.
Figure 12 shows two species of beetles Source: Reference 5
By the end of the decay, the white, fat, three-year-old maggots began to pack up and leave the corpse in a big way, ready to find a comfortable place to pupate quietly. Adult beetles are also leaving, and their larvae are pupating.
Figure 13 shows babies waiting to metamorphose Source: Reference 1
It should be noted that the insects that appear on the corpses are not only scavengers, but also insects that prey on them. For example, the scavenger beetle described above. In addition, insect-eating arthropods such as spiders and scorpions may also appear.
For example, the cryptoptera insects that reach the corpse during the swelling period have been feeding on the larvae of maggots or other beetles, and when they leave the corpse to prepare for pupal, the cryptoptera even tracks all the way and continues to prey on them.
Figure 14 shows several types of cryptopteratophans Source: Reference 5
Figure 15 shows a cryptid beetle that is feeding on a beetle pupa (and sure enough, where there is a worm, there is a river and lake...). Source: Reference 4
The fourth stage is the drying period
Most of the tissue of the corpse has been eaten clean, leaving only hair, bones, and a small amount of dry, hard soft tissue.
Most of the insects have left, and the remaining beetles are mainly some skin nymphs, and some mites that prefer dry environments (these species of mites are also often found in places that have not been inhabited for a long time, such as storage rooms, houses that have not been inhabited for a long time), ants, etc.
Stage V : Wreckage Phase
The body was further eaten up and nearly bone-white.
There are basically no insects staying here, only some species that inhabit occasionally.
So far, we have witnessed a process of corpse change that makes people feel sad, and nature's degradation of corpses has come to an end. The visiting insects, thriving on the remains of the creatures, complete the cycle of nature.
But how does the succession law of these insect fauna help solve the case? Let's move on.
In the movie "The Silence of the Lambs", the police extracted a pupa from the throat of the corpse, which was identified as a grimace moth of the Lepidoptera family. The grimace moth, on the other hand, lives only in Asia, and there is no such species in the region.
This means that the pupae has been artificially stuffed into the corpse, and it must have been kept by someone, and the criminal must have a channel to obtain it. This discovery provided a very valuable clue to the subsequent cracking of the case.
Figure 16 A pupae extracted from a corpse in "The Silence of the Lambs" Source: Screenshot of the movie "The Silence of the Lambs"
But what makes "forensic entomology" a big show is more in the field of judging the time of death.
Death time, also known as postmortem interval time (Abbreviation: PMI), in the field of "forensic entomology", it is actually a superposition of two time periods: one is the colonization time (English abbreviation: TOC), which means the time when a person dies and the adult worm comes to lay eggs; the other is the insect development calendar (Abbreviation: PIA), which means that it is calculated from the moment the egg is laid, until the time the insect develops to the stage of your collection.
The basic formula of forensic entomology is PMI = TOC + PIA
namely
Time of death = colonization time + insect development calendar
I believe that you have also seen a lot of suspense film and television dramas, the most common insect used to infer the time of death, that is, fly larvae, that is, maggots. In fact, maggots can be the priority object of forensic doctors for good reason.
Reason 1: Once the fly eggs on the carcass are hatched, the larvae feed only on the carcass to meet the needs of growth and development (because the source of nutrients required for its development is single. Suppose it also preys on other insects, which is an additional uncertainty);
Reason 2: The vast majority of flies do not lay eggs on live bodies (thus avoiding misestimations about the time of death);
Reason 3: The growth and development rate of the larvae is highly correlated with the outside temperature (how long it has developed can be reversed when the temperature changes and larval development stages are known);
Reason 4: Its species and development stage can be determined more accurately. (There are many kinds of flies, the developmental laws of different species are not the same, if the species is determined wrong, it will lead to errors in speculation; the same is true for the development stage, and the stage confirmation is wrong, which will also lead to errors).)
For these reasons, maggots are hot favourites in the field of "forensic entomology". However, due to its too many species (for example, there are more than 1300 species in 5 subfamily and 47 genera known to the lily family alone), even professional forensic entomologists cannot recognize them all, and for ordinary forensic workers, it is remarkable to be able to identify the level of the family, and to determine its species more specifically, you can only rely on professional entomologists.
So, going back to the case at the beginning of the article, the maggots with a cross-section of the neck of the headless corpse became an important clue for the forensic doctors to infer the time of death, and they took samples to observe and examine the maggots at the scene, and finally calculated that the death time of the deceased was 16 days ago.
This clue has played a very important role in the circle of the suspect, and after the murderer was arrested, the time of the killing he confessed was only one day different from the time previously calculated.
Life is like a meteor that crosses the boundless darkness in the eternal long night, and it comes from the boundless darkness and returns to the boundless darkness. It is fortunate to be able to give birth to an individual with consciousness from this cold universe, and in the last moment when it is about to return to this vast universe, this skin bag can also nourish many other small beings and have a wonderful encounter with them, which is actually a kind of fate.
Seeing this, I believe you have a preliminary understanding of forensic entomology.
So, in practical applications, how does forensic doctors calculate the time of death? Before answering this question, let's challenge a real-world case:
On June 15, a body was found somewhere. The best developed on the carcass was the neo-luteo larvae, on which forensic doctors extracted the species's third-instar larvae. Now from the nearby weather station to measure the local daily average temperature in recent days, through correction, estimate the average temperature of the scene in recent days (the site temperature is not equal to the temperature data of the weather station, so it needs to be corrected to improve the accuracy of the estimate, the correction method is not detailed here). This is shown in the following table:
It is now known that at similar temperatures, the effective accumulated temperature of the species from the development of the fly eggs to this stage is K = 65.2 days, while the initial developmental temperature of the larvae is 12.5 °C.
I ask you: On what day did the deceased die?
Does it feel like there are many terms and one black eye?
It doesn't matter, we have prepared an advanced version of the forensic entomology practical guide for readers with strong calculation ability and exploration, please click on the second picture in today's update to see if you have the potential to become a forensic entomologist! (The terms in the title will be introduced in the second picture and text)
So, what other interesting stories about insects solving crimes have you seen in TV series or novels? Feel free to leave a message in the comments section to share with us.
References: [1] Forensic Entomology: The Utility of Arthropods in Legal Investigations, Jason H. Byrd & James L. Castner; ISBN: 978-0-8493-9215-3;[2] The Science of Forensic Entomology, David B. Rivers,Gregory A. Dahlem; ISBN:978-1-119-94036-4; Hu Cui. Forensic Entomology[M].Chongqing: Chongqing Publishing House, 2000;[4] Biology of Rove Beetles, Oliver Betz, Ulrich Irmler, Jan Klimaszewski; ISBN: 978-3-319-70255-1; [5]《The Book Of Beetles》，Partice Bouchard; ISBN:978-1-78240-232-9;[6]Chen Lushi. Chinese cadaver flies[M].Guizhou:Guizhou Science and Technology Press,2013. [7] Source of the title of this issue: "Silent Lambs" Stills Editorial Board of this issue: Main Manuscript - Tooth Tip; Reviewer - Lulu Xiu / Bao Bao; Quality Inspection - Adin; Consultant - I Am Around You / Lao Qin
This article is an original article and will not be reprinted without authorization