“If all mankind were to disappear, the world would regenerate back to the rich state of equilibrium that existed ten thousand years ago. If insects were to vanish, the environment would collapse into chaos.” E.O. Wilson, father of the modern naturalist movement.
In this series of blogs, Te Papa entomology curator and forensic entomologist Julia Kasper looks at some of her favourite ways insects help humanity. Together with Auckland-based MSc student Xenia Okeremi, she explains how flies can help solve crimes.
Attitudes towards insects are often negative, and extensive efforts are made to kill them when damage to crops or health is involved. Insects such as mosquitoes, fleas, and lice are widely reviled even though very few species directly harm humans. No more than 1,000 insect species can be considered pests. That is 0.1% of the one million species of insects described so far! Mostly, insects provide benefits to us. They are a source of food, textiles, and medicine and are valuable models for studying biological processes, including genetics, physiology, and biomimicry. The importance of insect ecological services can’t be understated, with the annual global economic impact of pollination, recreation (e.g. fishing), dung burial, and pest control estimated at $USD 153 billion. Insects do a lot for us and deserve our gratitude and respect.
When did Forensic Entomology become a thing?
Forensic Entomology is the study of insects applied to legal investigation. The first documented use of forensic entomology was in the 13th century in China conducted by Sung Tz’u, who was known as the death investigator at the time. In a rice field, a man was killed, and his stab wounds suggested a sickle, commonly used by fieldworkers, as the murder weapon. Tz’u called all the workers together and asked them to set their sickles in front of them Only one sickle was attracting flies, sensing traces of blood. The owner of the sickle then confessed to the crime.
In Europe, people didn’t understand much of the life cycle of insects until the 17th century, but it wasn’t until the dawn of the 20th century when entomology was applied in the field of forensics. During the autopsy of a mummified child found in a chimney in 1855, a French doctor named Bergeret, noticed the presence of larvae and numerous pupae and determined an approximate time when the eggs would have been laid for larvae to be found on the corpse. This was used to help get an understanding of how long the body had been in the chimney and which of the four possible tenants were living in the house at the time that the body was placed.
Mégnin, another French doctor, formulated a theory on the predictable ecological waves of insect life on corpses, which he published in his book La Faune des Cadavres in 1894. To this day, the principles of Mégnin’s work form the basis of forensic entomology.
What happens after death?
Different insect species are found on a corpse at different stages in the decomposition process and the decomposition can be split into five stages. The fresh stage, in which the chemical breakdown attracts insects within the first 10 minutes after death, lasts for two days.
The bloated stage is highly attractive to insects and lasts approx. a week, followed by the active decay stage when proteins and ammonia start to ferment. The carcass temperature drops, and the larvae leave the body to pupate, indicating the beginning of advanced decay stage, which persist until 10-23 days after death. Left behind is a carcass made up of bone, cartilage, hair, bits of tissue. The final stage, the dry remains stage, starts at day 18 and continues past day 90. This stage is comprised of mainly just bones. As the remains start to dry out the insect population is dominated by beetle species.
The succession of insects settling on a corpse always follows a certain pattern and is therefore predictable, because carrion flies and other necrophagous (corpse or carrion eating) arthropods are attracted by different emitted chemical volatiles. These let an insect know if the decomposition stage of the body is right for it or its offspring to use as a food source.
However, the time periods of the insect succession are extremely variable and depend on multiple external factors, such as temperature, habitat, and exposure of the body.
In order to utilise insects for medico-legal matters, a thorough knowledge of all relevant species is necessary, including life histories and duration of their lifecycles.
The most common insects on a corpse are Diptera (true flies) of the families Calliphoridae (blow flies), Sarcophagidae (flesh flies), lesser houseflies (Fannidae) and house flies (Muscidae).
The life cycle of a fly includes the egg, then three larval instars (maggots) that need to shed their skin to grow, the pupa and the adult fly. Development time is influenced by external factors such as temperature, with warmth hastening the process.
How can FE help to solve a crime?
Today, forensic entomology is applied not only in criminal case investigations, but also in civil areas, such as insect infestation of food products or dwellings.
Within a criminal context, forensic entomology is useful in finding locations of events important to a case, or if wounds are present. It can also be utilised in cases of child and elderly neglect or abuse, in cases of drug abuse, and to track the country of origin for drug shipments.
But mainly forensic entomology is used in cases to determine the minimum postmortem interval (PMI) of a body (the estimation of the minimal time that has passed since death occurred).
Once a corpse has been found, the insects must be collected immediately. This is usually done by the police or ESR (Institute of Environmental Science and Research) in New Zealand. The entomological evidence is then sent to a forensic entomologist, like Julia. After receiving the specimens, she needs to identify the species.
The development rates of the species must be known, so Julia can calculate the PMI, measuring the size of the larvae…
… and taking the ambient temperature over the past few weeks, and many more factors into account:
How well is FE researched in New Zealand?
The study of carrion insects within New Zealand and Australia was initially focused on fly strike in sheep and as the topic became more popular during the 1980s, these studies evolved to incorporate practical forensic entomology. This led to New Zealand’s first known forensic practitioner, who used his casework to study all insects that were found on corpses across the Auckland region between 1981–1983. However, the first systematic field study, also for the Auckland region, was only published in 2007.
The major contributor to FE in NZ was Dallas Bishop, who has recorded the species found on bodies from 1993 to 2021 and which have been used to calculate PMI. Unlike previous studies, Bishop covered all regions of New Zealand. More studies have followed in recent years, as it has become evident that forensic entomology is still poorly understood in the New Zealand context.
The insects known to settle on a body can wildly vary geographically due to differences in present biota and climate. This is even more relevant for New Zealand with its remote location and unique flora and fauna. The species endemic to Aotearoa New Zealand and relevant for forensic entomology haven’t been investigated in depth. Additionally, the fact that there were barely any mammals that could provide a scavenger meal for millions of years would have a strong effect on the necrophagous fauna. While insects introduced to New Zealand, such as Calliphora vicina or Lucilia sericata, are more abundant around humans and well-studied overseas, they would have adapted to New Zealand’s unique conditions over time.
Given the large effect that climate has on insect growth, the application of overseas research data from is limited for New Zealand. That’s why Xenia is currently rearing blowflies under different conditions to improve the accuracy for PMI calculation in New Zealand.
Are there any maggots at Te Papa?
Yes, we have an “Insectarium” which is basically a bug nursery, like most natural history museums. Live insects make attractive display material for outreach activities, such as public programming and education here at Te Papa:
Having the opportunity to keep live insects is also necessary to support certain research projects. Sometimes we only know one life stage of a species, sometimes even only one sex.
To identify and describe all developmental stages (egg, larvae, pupa adult male and female), rearing is often the only realistic possibility to see those undocumented stages. For example, many larvae of Diptera are either completely unknown or we cannot match them to adults of the same species. Read about projects that include rearing of fly larvae for taxonomic reasons:
However, a species is more than its morphological features. In order to study a species, we need to know more about its functional biology. This can be extremely difficult in the field, and systematic studies are necessary – for example the attraction to certain volatiles (host recognition) of mosquitoes or the fungus gnats, mentioned above.
Our insectarium is also used to rear blowfly larvae to support the Institute of Environmental Science and Research (ESR) and the New Zealand Police.
But that’s not even the end of our bug exploitation. We use necrophagous beetles for our collection management as this video discusses:
Highlighting the benefits of insects is fascinating, how has forensic entomology advanced human understanding in criminal investigations? Regards Telkom University Jakarta