Blood vs. Carrion: Forensic Entomology Informs Human DNA Profiling

Introduction

Since the first DNA-based exoneration in 1989, DNA evidence has helped free over 600 people wrongfully convicted of crimes by 2024 (“The National Registry of Exonerations,” n.d.) [1] , demonstrating its application in criminal investigations, missing person cases, and mass casualty events is vital (Turngan et al., 2019) [2]. DNA is used in these cases because many bodily fluids, such as bloodstains, saliva, or semen, contain DNA that can be analyzed to identify who was at a scene. While humans share 99.6% of DNA with each other, the 0.4% difference allows for identification against a reference sample (“Fact Sheet: Human Genomic Variation” 2023) [3]. For example, blood could be drawn from a suspect (the reference sample) for DNA profiling and compared to the DNA profile of unknown bodily fluids retrieved from a murder scene. Unfortunately, DNA evidence from bodily substances at a scene cannot be retrieved most of the time, either because the perpetrator cleaned the scene, or simply because the crime left no samples to take. However, there is a source of DNA that is available at almost every crime scene: insects.

 An essential part of insects’ viability in forensics is their prevalence, as they live on every continent, in every environment (“What Is an Insect?” 2024) [4]. Insects are often associated with finding the postmortem interval, or the time since death, but their feeding habits can also help identify a human. Many common insects feast on humans in ways that turn them into DNA sources. This includes hematophagous (blood-eating) insects like mosquitoes, and necrophagous (carrion-eating) insects like flies (Durdle, 2019), that fed off of the bodily fluids of those present during or after a crime [5]. DNA of such figures can be extracted from these insects’ digestive tracts and used to build a DNA profile. This can be used to identify a victim when the body is either missing or too degraded to visually identify, or a suspect if the perpetrator left their own bodily substances at the scene (such as blood if the victim had fought back or saliva if the perpetrator was careless).  Due to this potential, researchers have begun to explore the use of insects with DNA analysis. This review aims to survey recent research on two aforementioned types of insects – hematophagous and necrophagous – in forensic science and compare them as DNA sources, emphasizing the efficiency of DNA collection for a DNA profile. As DNA analysis becomes more sensitive to smaller amounts of DNA, criminalists need to be aware of the prevalence and effectiveness of insects as a tool in DNA profiling (Lim & Majid, 2020) [6].

Hematophagous Insects

Hematophagous insects feed on human blood, which can be extracted from the insects to recover the DNA. The two most common members include mosquitoes, as the females must feed on blood for egg production (Ahmed et al. 2023), and wingless bed bugs, which infest beds, couches, and other resting furniture [7].

Mosquitoes

The species of mosquito and its subsequent feeding habits affect how long post-blood meal (PBM) DNA can be useful (Ahmed et al. 2023; Talebzadeh et al. 2023) [7, 8]. Post-blood meal is the time after blood has been ingested by an organism. Researchers have also noted that certain species of mosquitoes have preferences for gender, warmer bodies, and even animal species. In recent literature, mosquitoes that prefer female humans, stay near where they fed for a longer time, and feed for longer are more likely to be useful to forensic investigations. All of these behavioral habits contribute to a longer PBM, which is important because insects digest the blood they eat. Blood that has not been fully digested means a greater chance for viable DNA extraction, so forensic scientists can collect and analyze DNA with greater accuracy. The DNA that works best for forensic scientists exists on a time limit before complete digestion renders it unreadable. 

In one study, it was found that polymerase chain reaction (PCR) could be used to amplify, or create more copies of, DNA in the Asian malaria mosquito (Anopheles stephensi) even after the mosquito gut had digested it, as it was detectable from up to 84-108 hours PBM (Talebzadeh et al. 2023) [8]. The researchers used the Alu elements, or “jumping genes” that are unique to primates. These elements are a type of DNA segment that are well studied in the human genome, which makes their use as a marker essential.  The 16S ribosomal RNA and cytochrome b (cytB) markers, from mitochondrial genes (mtDNA), were also used due to their features that allow for the reliable identification of blood meal origin. These features include, but are not limited to: maternal inheritance, very high copy numbers in each cell, lack of recombination. The accuracy of PCR replication was found to depend on the length and copy number of a loci for amplicons. Loci are the specific locations of a gene on a chromosome. Amplicons are the DNA that is used and produced when creating more copies of DNA. In other words, the length and the number of variations in repeats of a specific range of genes in our genome affect the accuracy that short strings of DNA are amplified by PCR. (Talebzadeh et al. 2023) [8]. 16S RNA had a significantly higher PCR success rate compared to cytB, the other mtDNA, due to its smaller amplicon. The Alu-repeat amplicons, with a higher copy-number amplicon, had a statistically significant difference in PCR success rate compared to cytB, but the 16S RNA was at about the same success rate as the Alu-repeat amplicons. The 50% success rate for PCR for the compact high-repeat DNA was 117 hours (Alu) and 113 hours (16S RNA). In comparison, the long low-repeat DNA had a 50% success rate for PCR at 86.4 hours. The researchers noted that in amplifying the regions of DNA collected from mosquitoes, the shorter amplicons and the higher copy number loci result in recovery with the longest PBM time. This implies that compact DNA containing many repeats is suited to surviving the digestive system of a mosquito. This information will be useful to researchers who conduct further research, as the reason why this is true remains unknown. In a case where there are no bed bugs and there is no body, forensic scientists should consider collecting mosquitoes around the area for evidence.

Another concern for research relates to the mosquitoes' feeding habits. Mosquitoes may also feed on multiple animals. This means that DNA from other hosts can contaminate the collection of human DNA, potentially degrading the latter’s recovery due to the composition of the non-human sources of blood. A different study found that common house mosquitos (Culex pipiens) that consumed mixed blood samples showed reduced PBM for good human DNA to be collected. In addition, female human samples resulted in the longest PBM where human DNA could still be collected (Ahmed et al. 2023) [7]. Compared to the typical duration of 60-72 hours for the species to fully digest a blood meal, the authors were able to obtain full profiles of 24 STR loci commonly used in forensics up to 36 hours PBM from mosquitoes fed only female human blood but only up to 12-24 hours PBM when fed a mix of male-female human blood or a mix of human and mouse blood. However, loci from mixed blood groups degraded at a faster rate than single blood groups past their respective full-profile window. The researchers of this experiment note that human female blood may have a different composition compared to human male and mouse blood, which allows for it to take longer to degrade (Ahmed et al. 2023) [7]. More research must be done to explain why human female blood lasts longer in mosquitoes. While this research does provide evidence for common house mosquitoes to be used in a forensic case as a source of human DNA due to the blood the mosquitoes feed on, the consideration of mixed blood increasing degradation must be taken into account. Mosquitoes are a useful backup tool for forensic scientists when better sources of DNA are unavailable, but they must be aware of the possibility of mixed blood samples within mosquitoes. 

Although mosquitoes are a possible source of human DNA, they may feed on more than one person or contaminate a location that is not relevant to an investigation (Durdle 2019) [5]. Because of this, researchers have turned to bed bugs due to their ability to produce highly accurate DNA profiles as an alternative. (Durdle 2019; Schal et al. 2018) [5, 9].

Bed Bugs

Bed bugs feed on human blood throughout their life cycle (Schal et al. 2018) [9]. This means that there is a higher chance of finding a bed bug that has fed on the human of interest for a forensic case, leading to a higher chance of being able to extract DNA for amplification and profiling. However, bed bugs will only feed on a living host, so their use could be restricted, which is why mosquitoes may be used as a backup (Schal et al. 2018; Durdle 2019) [5, 9]. As will be seen, bed bugs have mounting evidence that DNA can be extracted from them with much longer PBM times, compared to mosquitoes. As with mosquitoes, the efficiency of DNA extraction PBM times varies based on what variables the researchers are focusing on. 

Extraction of DNA from bed bugs is much more efficient and reliable, as DNA can be recognized as human for up to thirty days PBM (Lim and Majid 2020) [6]. Bed bugs tend to have more intermittent feeding habits, which may be why bed bugs are linked to longer PBM detection of DNA compared to other insects. Researchers of one study found that female tropical bed bugs (Cimex hemipterus) can provide about 66.67% success rate of identifying the blood consumed as coming from a human after 14 days PBM. At 30 days PBM, the success rate drops to about 33.33%. In addition, the researchers found that the D18S51 marker, which is used to determine if the DNA is from a human, is a better marker than the HRV1 marker, another human DNA marker. The HRV1 marker could not provide a success rate after 5 days PBM (Lim and Majid 2020) [6]. This study shows that bed bugs, specifically the tropical bed bug, can be used as a source of DNA to determine that a human was the victim of bed bug feedings for up to 30 days PBM. Bed bugs tend to stay where they feed, so investigators may use this as evidence to link the human that was fed on to the bed bug’s location, which could be a crime scene. Crime scenes are not always apparent and there are not always bodies available for forensic scientists to discover evidence. In these cases, DNA is a useful tool since the DNA in the blood that the bed bugs feed on can be used against reference samples. Furthermore, if there appear to be bloodstains in a location, investigators can look for bed bugs to confirm that the bloodstain was more likely to be human than a different animal. Other studies can then shed light on matching DNA from blood to a reference DNA profile. 

The common bed bug (Cimex lectularius) is another candidate for DNA typing of humans. Schal et al. found that with short tandem repeats (STR) analysis, identification was possible between 72-108 hours PBM depending on whether it was male, female, or mixed blood samples [9]. The female samples allowed for identification after the longest time PBM. At 96 hours, the female blood samples were the only ones to show about 35% of samples having complete profiles. The male blood samples had dropped to 0% by 96 hours and the pooled blood samples had dropped to 0% by 84 hours (Schal et al. 2018) [9]. STR analysis uses the short repeating patterns in human DNA to create a human DNA profile and has become the standard for forensic DNA typing (Keerti and Ninave 2022) [10]. As with the mosquito study by Ahmed et. al, bed bugs feeding on female humans tend to produce higher percentages of samples with complete profiles (Ahmed et al. 2023; Schal et al. 2018) [7, 9]. Regardless of the type of insect, female blood appears to be different from male blood, allowing for a higher chance of complete profiles. This pattern of results is a possible field of future study in using insects as DNA sources. In addition to creating STR profiles, the researchers investigated STR autosomal markers of different molecular weights, or the mass of a molecule. Lower molecular weights in markers, such as the D3S1358 marker, can be recovered at greater amounts for longer PBM times (Schal et al. 2018) [9]. This might be linked to the process of gel electrophoresis, where heavier molecules do not travel as far across the gel due to them being heavier and larger. The opposite is true for lower molecular weights. However, the researchers do not explain why this pattern occurs, suggesting an area of future study. Another pattern from the mosquito studies was that shorter amplicons tended to result in better recovery of DNA through PCR with longer PBM times. In addition to STR autosomal profiling, bed bugs have been found to provide Y-STR profiles, which are specific to human male DNA.

Y-STR profiles are based on the short tandem repeats on the Y chromosome, which makes Y-STR profiles specific to human males. Y-STR profiling is important for cases where it is necessary to be able to differentiate between male and female human DNA. From common bed bugs, complete Y-STR profiles were able to be made in one study for human male blood only after 72 hours PBM and for mixed human male and female blood after 60 hours PBM (Meiklejohn, Schal, and Lodhi 2025) [11]. These PBM numbers are similar to previous studies, indicating that there is a certain time range that investigators could utilize when collecting evidence at a scene. This research tracked the loci for Y-STR profiling and found that shorter loci tended to have more DNA compared to medium or long loci (Meiklejohn, Schal, and Lodhi 2025) [11]. This matches with previous studies and serves as a pattern for future research to try to understand. Y-STR profiles are possible with bed bugs, although the researchers acknowledge that bed bugs were immediately stored at cold temperatures and in ethanol after feeding, which means that blood collected from bed bugs in an active crime scene may not provide the same accuracy. Future studies could look into how temperature affects DNA collection and analysis. The behaviors and biological adaptations of bed bugs can be linked to the fact that human DNA can be detected for longer PBM compared to mosquitoes, which makes bed bugs the insect of interest for forensic scientists. 

Both bed bugs and mosquitoes require more in-depth research in their quality of analysis of human DNA for identification and to determine what other environmental factors may affect DNA extraction. Bed bugs appear to contribute more accuracy in DNA analysis compared to mosquitoes, but mosquitoes are not restricted to pieces of furniture dedicated to resting. Both bed bugs and mosquitoes need to be options for forensic scientists as any DNA evidence could be of importance to a case. Bed bugs and mosquitoes have shown promise as vectors of human DNA, but their feeding behaviors restrict them to use with live hosts. In forensics, there may be a deceased victim, which leads to necrophagous insects as potential human DNA sources.

Necrophagous Insects

While hematophagous insects can serve as human DNA sources for live hosts, necrophagous insects can provide information about deceased individuals and may be used to identify an unknown body, identify if there are two different DNA profiles in a location or on a body, or link a victim to a suspect. Flies of varying species have shown great potential for this purpose. 

Flies are well known for being decomposers. Forensic scientists have realized the great benefit of flies for the collection of DNA in the possible identification of cadavers. Unlike bed bugs, flies feed on various biological substances, which makes them uniquely versatile in the types of cases they can be used for. Flies do not only feed on blood. They can feed on flesh, saliva, and other biological matter. Different species of flies feed on different materials, which can be seen from the differences in fruit flies and blowflies. Fruit flies tend to eat fruit and sugary substances, which is why they are often found in households around fruit. Blowflies feed on decaying flesh, making them the ideal species of fly for forensic scientists. Cases where no bed bugs or blood are present at a crime scene would benefit from flies. However, a downside that forensic scientists must keep in mind when collecting DNA from flies is that they may have mixed samples of DNA due to feeding on more than one source of human biological fluids. 

Most research has found that the early life stages of flies yield the most DNA for collection and detection (Deymenci et al. 2023; Chamoun et al. 2020; Durdle 2019; Powers, Oorschot, and Durdle 2019) [5, 12, 13, 14]. According to Chamoun et al., human Y-STR DNA was recovered after fourteen days of decomposition from larvae and pupae of Chrysomya albiceps, the banded blowfly or the green bottle fly, with pupae mostly being collected after day eleven of the pig body being left outside [13]. Larvae were mostly collected up to day ten, as this is the first stage of an insect’s life cycle, with pupae being the next stage. After day eleven, most of the larvae have grown to the pupae stage (Chamoun et al. 2020) [13]. DNA can be extracted from the blowflies that are feeding on a deceased victim. The study that was specific to blowflies also noted that larvae were found underneath the ground around and under the body of the pig subject. This suggests that not only can DNA be extracted from the flies in their adult form on a body, but if the body were to be removed from the scene before a forensic team could collect evidence, the larvae and pupae of the flies could allow for DNA extraction. For this study, the more specific human Y-STR DNA was the target for DNA extraction, as this type of DNA is useful for possible rape cases (Chamoun et al. 2020) [13]. Y-STR DNA allows for the identification of male individuals. For sexual assault cases, blowflies can be a powerful tool to narrow down the suspect pool for investigators as the suspect may have left semen or blood at the scene. Blowflies are just one species of many that have been aiding forensic scientists in this way. Another species of fly has been used for even more specific and physical profiling. 

The common green bottle fly has provided evidence that the DNA collected from insects can be utilized to predict the hair and eye color of a suspect or a victim (Deymenci et al. 2023) [12]. The common green bottle fly is an early settler on a decomposing body, which makes this species of fly of particular interest to forensic scientists. Many necrophagous insects, including the common green bottle fly, have a crop in their larvae form, which is a place for food storage when the food requires more time to digest. This biology allows for extraction of DNA from the crop, but the digestion of DNA is still an issue. In another study, maggot debridement therapy (MDT), where maggots were used to feed on the dead tissue of chronic diabetes patients, was used for ease of collection of larvae from volunteers. The researchers were able to successfully genotype 83.33% of samples. Of those samples, 56% accurately predicted hair color, and 68% accurately predicted eye color (Deymenci et al. 2023) [12]. While the results show that the researchers can only accurately predict hair and eye color a little over half of the time, the DNA from necrotized tissue can be used to form a genotypic profile from which a prediction can be made. The genotype profile can be more accurate than the phenotype profile since the genotype is the set of alleles inherited for a gene whereas the phenotype is the physical manifestation of the genotype. The genotype refers to the sequence of DNA that the individual has for a particular region of DNA, while the phenotype depends on both the genotype and other factors. The phenotype may be affected by the environment, making it more difficult for an accurate profile to be made. The prediction of physical characteristics may help investigators narrow their search to a group of individuals. Often, victims are decomposed to the point that they are unrecognizable. There may also be a case where the body was only partially recovered, making it more difficult for identification. In a case with a missing person or a mass disaster that resulted in multiple bodies, this information could help investigators with creating a sketch of the victim for identification.

These research articles reveal that as DNA technology becomes more sensitive and accurate, flies provide a great opportunity to collect DNA for analysis when a corpse is not physically present, or for when the DNA of the decomposing body is too degraded to be useful. The DNA extracted from flies can even be used to begin to predict the physical appearance of a victim or suspect, which would be useful to law enforcement in gaining direction for an investigation. 

Conclusion

Currently, there is compelling evidence to support the use of insects as DNA sources in forensics. The two main types of insects that forensic scientists have researched for this application are hematophagous and necrophagous insects. While hematophagous insects have been shown to produce the most complete DNA profiles, necrophagous insects can be used in cases where a decomposing body is the only source of human biological substances. Among hematophagous insects, bed bugs are the most reliable for providing accurate DNA profiles over the longest periods of PBM time, but mosquitoes should still be considered a backup for when bed bugs are not available as mosquitoes have shown promise in creating DNA profiles as well (Lim and Majid 2020; Schal et al. 2018; Talebzadeh et al. 2023; Ahmed et al. 2023) [6, 7, 8, 9]. Flies are a great candidate for DNA analysis as they feed on bodies in earlier stages of decomposition when DNA is less degraded (Powers, Oorschot, and Durdle 2019; Chamoun et al. 2020) [13, 14]. As DNA analysis techniques continue to advance, it is crucial to further explore DNA collection from various sources, particularly from insects, whose abundance aligns with their increasing use in research.

About the Author: Mackenzie Anselmi

Mackenzie Anselmi is a fifth year Biological Sciences Major graduating in December 2025. She is interested in forensic science as a result of watching Sherlock and taking a high school Forensic Science class. She wrote this review for UWP 102B with her instructor Russ Carpenter. Throughout her college classes, she has found herself drawn to genetics as it connects to her many passions, including forensics and psychology. She hopes to use her knowledge to research how genetics relates to our mental health and the choices that people make.

Author’s Note

I am interested in becoming a forensic scientist with DNA as my specialty. There are so many cases out there, cold cases and new ones, where DNA could have saved people associated with an investigation a lot of time and pain. Innocent people are often dragged into cases that do not have DNA evidence. Families of victims usually wait a long time to get justice or do not get it at all. Yet, DNA evidence is still not perfect. I wrote this piece for other undergraduates who are going into the forensic master’s program specifically to emphasize the importance of DNA in this field and other ways to view its use. For other undergraduates in science, I would like them to walk away with the knowledge that often there are tools in a field that have been used before, like insects in forensics, but that they must think out of the box to find new, interesting ways of using those tools to help others with common problems in their scientific field.

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