Malaysian Scientists Recover Human DNA From Bed Bugs Up to 45 Days After Feeding

A Hidden Source of DNA in Tropical Bed Bugs

Scientists at Universiti Sains Malaysia (USM) have recovered human DNA from tropical bed bugs up to 45 days after the insects fed, opening a possible route for criminal investigations when bloodstains or other biological evidence are missing or have been removed.

The research focuses on Cimex hemipterus, a species common in Southeast Asia, Africa and parts of South America. Under controlled laboratory conditions, researchers obtained complete human genetic profiles immediately after feeding and partial profiles weeks later. Some of those partial results provided enough information to predict hair, skin and eye colour.

The work began with bed bugs collected from cushioned seats at Kuala Lumpur International Airport in 2014. Over the following decade, USM entomologist Abdul Hafiz Ab Majid and his team, including postdoctoral researcher Lim Li, investigated whether the blood inside these insects could become useful forensic evidence.

The findings, published in scientific journals and highlighted internationally, represent the first documented forensic application involving this tropical species. Earlier forensic studies had concentrated on Cimex lectularius, the common bed bug associated with temperate regions.

For investigators, the attraction is straightforward: an insect hiding near a bed or inside furniture may contain human genetic material even when there is no visible blood nearby. USM has also developed collection and laboratory procedures and tested specimens from infested sites in Penang, Malaysia.

As of July 5, 2025, the technique remains a research development requiring further technical and legal validation before routine courtroom use. The central challenge is turning DNA recovered from an insect into evidence that investigators can interpret reliably, particularly when the insect has fed on several people.

How the Researchers Tested the Blood Meals

USM scientists allowed bed bugs to feed on human volunteers under controlled laboratory conditions. They then extracted DNA immediately after feeding and at intervals of five, 14, 30 and 45 days.

The team used two established genetic methods: Short Tandem Repeat (STR) analysis and Single Nucleotide Polymorphism (SNP) analysis. Both are used in forensic science, with STR testing supporting identification and selected SNPs providing information about physical traits.

Associate Professor Abdul Hafiz Ab Majid described how the results changed as the insects digested their meals:

Right after feeding, we could recover full genetic profiles using STR and SNP methods. And even 45 days later, we were still able to retrieve partial profiles—enough, in some cases, to point to hair, skin and eye colour.

Digestion gradually breaks down the human DNA inside a bed bug. That explains why complete profiles were available immediately after feeding while later samples yielded less genetic information. A partial profile contains results for only some of the DNA markers being examined.

The research developed through several stages:

• 2014: Scientists collected bed bugs from cushioned seats at Kuala Lumpur International Airport.
• Over the following decade: The USM team studied how well the insects preserved human DNA after feeding.
• Laboratory testing: Researchers examined samples immediately after feeding and after five, 14, 30 and 45 days.
• Field testing in Penang: Scientists applied collection and analysis procedures to insects from infested locations.
• By July 5, 2025: The work had produced laboratory findings and a practical protocol, with further validation still needed for routine forensic use.

Why Bed Bugs Can Preserve Useful Clues

Bed bugs are familiar as pests that cause itchy bites and stubborn infestations in homes, hotels and public spaces. Their feeding habits also make them potential collectors of human DNA.

Nymphs and adults require blood meals to grow and reproduce. Both male and female specimens can therefore be relevant to an investigation. Mosquitoes offer a contrast because only females feed on blood.

Bed bugs are also wingless and tend to remain close to their feeding sites, retreating into nearby cracks and crevices after a meal. That behaviour gives investigators a reason to examine insects found around an area of interest, where their blood meals may contain DNA from people who were present.

The length of time DNA survives is another attraction. Human DNA in mosquito blood meals typically degrades within 26 hours, compared with the recovery of human DNA from bed bugs up to 45 days after feeding in the USM work. Forty-five days equals 1,080 hours, illustrating the much longer period examined in the bed bug research.

Rising bed bug infestations worldwide, particularly in cities and travel hubs, also increase the likelihood that investigators may encounter the insects at crime scenes. Their value would be greatest where conventional biological evidence is absent, damaged or deliberately cleaned away.

What STR and SNP Tests Tell Investigators

STR analysis examines short sequences of DNA that repeat. The number of repetitions varies greatly among individuals. By checking several locations, known as loci, a laboratory can build a genetic profile for comparison with a person's DNA. STR analysis is a standard method for human identification in forensic laboratories worldwide.

SNP analysis looks at changes in single letters of the DNA sequence. Certain SNPs are associated with characteristics such as eye, hair and skin colour. This can help produce investigative leads about appearance, while SNP analysis can also provide information about ancestry.

The two methods answer different practical needs. STR results help laboratories compare genetic profiles. Selected SNP results can help investigators assess physical characteristics, including when the DNA is degraded or incomplete.

USM researchers used both methods on DNA extracted from bed bugs. They also used HIrisPlex-S, a web based system that predicts physical traits from SNP data. In the experiments, the predictions matched the known characteristics of the human volunteers.

A prediction about appearance gives investigators a lead to examine. Its usefulness depends on which genetic markers can still be recovered from the insect. As digestion reduces the available DNA, the amount of information available for either comparison or trait prediction also falls.

Taking the Method From Laboratory to Penang Sites

The USM team developed a practical protocol for collecting, preserving and analysing bed bugs from potential crime scenes. Published in Forensic Science International, it sets out procedures intended to protect the human DNA inside the insects while reducing contamination from their outer surfaces.

The protocol covers several steps:

• Collect specimens from infested sites, including insects that are alive or dead and male or female.
• Preserve specimens in 70% ethanol and store them at minus 20 degrees Celsius to limit DNA degradation.
• Sterilise the surface of each insect to remove external contaminants before extracting DNA.
• Use STR analysis to generate human genetic profiles from the extracted material.

Surface cleaning matters because the research aims to examine DNA from a blood meal inside the insect. Removing material on the outside helps reduce the chance that external contamination will complicate the laboratory results.

Field tests in Penang extended the work beyond insects fed under controlled conditions. Most specimens yielded enough human DNA for partial or complete STR profiling, showing that useful genetic material could also be recovered from insects collected in everyday environments.

The field results give the laboratory findings a practical foundation. They also expose a central difficulty: insects collected from an infested location may contain blood from more than one person, making their genetic results more complicated to interpret.

When One Insect Contains DNA From Several People

Bed bugs may feed on multiple people. An insect collected from a shared environment can therefore carry a mixture of human DNA rather than a profile from a single donor.

In the field samples, researchers often detected more than two alleles at certain genetic loci. An allele is a version of a genetic marker. Finding more than two at a location was an indication that the sample contained genetic material from multiple human sources.

Mixed profiles complicate the task of deciding which genetic results belong to which person. Investigators would need laboratory interpretation that accounts for those mixtures before using the findings to support a case.

Time adds another difficulty. Digestion progressively reduces the completeness of the profile, so a specimen may contain both a mixture of donors and missing genetic information. Partial profiles can still provide useful leads, but they may fall short of the requirements for legal admissibility.

The potential value is nevertheless concrete. Insects hiding in furniture or crevices could preserve genetic material after other traces have disappeared. That could give investigators an additional route to explore in a complex case, especially where there is little biological evidence to collect.

Why Routine Courtroom Use Still Needs Work

The USM research used polymerase chain reaction (PCR), a technique that copies selected DNA targets so they can be examined. The tests targeted one region at a time. These tests are slower and less efficient than the multiplex kits used in accredited forensic laboratories, which examine several targets together.

Wider adoption requires standardised procedures and validation across different testing systems. Laboratories need methods that can handle degraded DNA, mixtures and specimens collected under conditions outside a controlled experiment.

Legal acceptance is another part of that process. Bed bug evidence must undergo rigorous validation and gain acceptance within the forensic and legal communities before it can become a routine courtroom tool. The USM team is collaborating with forensic specialists to refine the methods.

No timetable for completing that process was given. For now, the research points to a possible supplement to conventional evidence and, in some circumstances, a possible alternative source when conventional biological traces are unavailable.

The work also brings together several disciplines. Entomologists study the insects and their feeding behaviour, geneticists examine the human DNA, and law enforcement specialists assess how the results could be collected and used in investigations.

How Blood Feeding Insects Have Helped Before

Forensic entomology is the use of insects in criminal investigations. Much of its established work involves flies and beetles, including using their presence and development to help estimate time of death or locate remains.

Recovering human DNA from blood feeding insects is a newer area. Mosquitoes and lice have previously been studied as possible sources of genetic material from the people they fed on.

Mohamad Anil Shah Abdullah, chairman of the Penang Crime Consciousness and Public Safety Society, described why bed bugs could be useful when a scene has little conventional biological evidence:

Sometimes, there's no blood or fluids at the scene. Insects like flies and mosquitoes have been used before but bed bugs don't fly. That makes them useful.

He also pointed to a case in Finland in 2008 in which police retrieved a suspect's DNA from a mosquito found in a stolen car. The example illustrates the investigative possibility of examining a blood meal inside an insect.

USM's work extends that approach to the tropical bed bug. The species matters because earlier bed bug research focused on Cimex lectularius. Studying Cimex hemipterus makes the work relevant to regions where the tropical species is common, including Southeast Asia, Africa and parts of South America.

What the Findings Could Change for Investigations

Investigators searching an infested location may eventually have another item to collect alongside conventional biological traces: the insects themselves. The USM protocol offers a starting point for preserving those specimens and examining the DNA inside them.

Bed bugs' tendency to stay near feeding sites gives the research a spatial dimension, while the survival of DNA for weeks gives it a temporal dimension. Together, those features could help investigators explore who had been present at a location and the period relevant to a case, alongside other evidence.

The retention period could also be useful in investigations where substantial time has passed before a scene is examined, including some cold case work. Its practical reach will depend on the condition of the specimens and how much human DNA remains recoverable.

As infestations spread internationally, procedures developed in Malaysia could be adapted elsewhere, especially in regions where Cimex hemipterus is common. The immediate achievement is a combination of laboratory recovery, testing in Penang and a published collection protocol. Turning those results into routine evidence now depends on resolving the technical and legal challenges.

Key Points

• USM scientists recovered human DNA from tropical bed bugs up to 45 days after feeding.
• Complete profiles were recovered immediately after feeding; later samples yielded partial profiles, sometimes sufficient for predictions of hair, skin and eye colour.
• The research began with insects collected at Kuala Lumpur International Airport in 2014.
• Most specimens tested from Penang sites provided enough DNA for partial or complete STR profiling.
• The collection protocol includes 70% ethanol, storage at minus 20 degrees Celsius and surface sterilisation before extraction.
• Mixed human DNA, digestion, testing procedures and legal validation remain challenges before routine courtroom use.