FORENSIC
ENTOMOLOGY : THE USE OF INSECTS IN DEATH INVESTIGATIONS
Dr. Gail S. Anderson, Associate Professor
Diplomate,
American Board of Forensic Entomology
School of Criminology, ¶¡ÏãÔ°AV
8888 University Drive
Burnaby, B.C.
V5A 1S6
Tel.
(604) 291 3589 (wk)
856 4058 (hm)
252 5785 (pager)
Forensic (or medico-legal)
entomology[1] is the study of the insects
associated with a human corpse in an effort to determine elapsed time since death. Insect evidence may also show that the
body has been moved to a second site after death, or that the body has been
disturbed at some time, either by animals, or by the killer returning to the
scene of the crime. However, the primary purpose of forensic entomology today
is to determine elapsed time since death.
Forensic entomology was
first reported to have been used in 13th Century China and was used
sporadically in the 19th Century and the early part of the 20th Century,
playing a part in some very major cases. However, in the last 20 years,
forensic entomology has become more and more common in police investigations.
In 1996, some of us developed the American Board of Forensic Entomology, a
certification Board for Forensic Entomologists, similar to the Board certification
available for forensic odontologists and forensic anthropologists.
Most cases that involve a
forensic entomologist are 72 h or more old, as up until this time, other
forensic methods are equally or more accurate than the insect evidence. However,
after three days, insect evidence is often the most accurate and sometimes the only method of determining elapsed
time since death. Recently, I have also analyzed and testified in cases in
which elapsed time since death was only a few hours previous to discovery.
There are two main ways of
using insects to determine elapsed time since death : -
I - using successional waves of insects
II
- using maggot age and development.
The method used is
determined by the circumstances of each case. In general, the first method is
used when the corpse has been dead for between a month up to a year or more,
and the second method is used when death occurred less than a month prior to
discovery.
The first method is based on the fact that a human body, or any kind of carrion,
supports a very rapidly changing ecosystem going from the fresh state to dry
bones in a matter of weeks or months depending on geographic region. During
this decomposition, the remains go through rapid physical, biological and
chemical changes, and different stages of the decomposition are attractive to
different species of insects. Certain species of insects are often the first
witnesses to a crime. They usually arrive within 24 h of death if the season is
suitable i.e. spring, summer or fall
in Canada and can arrive within minutes in the presence of blood or other body
fluids. These first groups of insects are the Calliphoridae or blowflies and
the Sarcophagidae (the fleshflies). Other species are not interested in the
corpse when the body is fresh, but are only attracted to the corpse later such
as the Piophilidae or cheese skippers which arrive later, during protein
fermentation. Some insects are not attracted by the body directly, but arrive
to feed on the other insects at the scene. Many species are involved at each
decomposition stage and each group of insects overlaps the ones adjacent to it
somewhat. Therefore, with a knowledge of the regional insect fauna and times of
carrion colonization, the insect assemblage associated with the remains can be
analyzed to determine a window of time in which death took place. This method
is used when the decedent has been dead from a few weeks up to a year, or in
some cases several years after death, with the estimated window of time
broadening as time since death increases. It can also be used to indicate the
season of death e.g. early summer. A knowledge of insect
succession, together with regional, seasonal, habitat and meteorological
variations, is required for this method to be successful.
The insect egg is laid in
batches on the corpse and hatches, after a set period of time, into a first
instar (or stage) larva. The larva feeds on the corpse and moults into a second
instar larva. The larva continues to feed and develop into a third instar
larva. The stage can be determined by size and the number of spiracles
(breathing holes). When in the third instar, the larva continues to feed for a
while then it stops feeding and wanders away from the corpse, either into the
clothes or the soil, to find a safe place to pupate. This non-feeding wandering
stage is called a prepupa. The larva then loosens itself from its outer skin,
but remains inside. This outer shell hardens, or tans, into a hard protective
outer shell, or pupal case, which shields the insect as it metamorphoses into
an adult. Freshly formed pupae are pale in colour, but darken to a deep brown
in a few hours. After a number of days, an adult fly will emerge from the pupa
and the cycle will begin again. When the adult has emerged, the empty pupal
case is left behind as evidence that a fly developed and emerged.
Each of these developmental
stages takes a set, known time. This time period is based on the availability
of food and the temperature. In the case of a human corpse, food availability
is not usually a limiting factor.
Insects are 'cold blooded',
so their development is extremely temperature dependent. Their metabolic rate
is increased with increased temperature, which results in a faster rate of
development, so that the duration of development decreases in a linear manner
with increased temperature, and
vice-versa.
An analysis of the oldest
stage of insect on the corpse and the temperature of the region in which the
body was discovered leads to a day or range of days in which the first insects
oviposited or laid eggs on the corpse. This, in turn, leads to a day, or range
of days, during which death occurred. For example, if the oldest insects are 7
days old, then the decedent has been dead for at least 7 days. This method can
be used until the first adults begin to emerge, after which it is not possible
to determine which generation is present. Therefore, after a single blowfly
generation has been completed, the time of death is determined using the first
method, that of insect succession.
PROCEDURE
The first and most important
stage of the procedure involved in forensic entomology involves careful and
accurate collection of insect evidence at the scene. This involves a knowledge
of the insects behaviour, therefore it is best performed by an entomologist. I am always willing to come to a scene if
it is possible. Unfortunately, the entomologist is often not called until
after the body has been removed from the death site. I usually see the remains
at the morgue, and in some cases, do not actually see the remains at all, so my
evidence is dependent on accurate collection by the
investigating officers.
COLLECTING, PRESERVING AND
PACKAGING SPECIMENS.
For further details, a video on insect collection is available from R.C.M.P. “E” Division Training – (604) 264 3619.
COLLECTION
Samples of insects of all stages should be collected
from different areas of the body, from the clothing and from the soil/carpet etc. Insects will often congregate in
wounds and in and around natural orifices.
The two main insect groups on bodies are flies (Diptera) and beetles (Coleoptera).
Both types of insect look very different at
different stages of their lives.
Flies can be found as:-
- eggs (in egg masses usually)
- larvae or maggots (in a range of sizes from 1-2 mm to 17 mm)
- pupae and/or empty pupal cases
- adults.
EGGS - are very tiny, but are usually laid in clumps or masses, and are
usually found in a wound or natural orifice, but may be found on clothing etc. They can be collected with a
child’s paint brush dipped in water or with forceps. Half should be preserved
in 75% alcohol or 50% isopropyl alcohol. The rest should be placed in a vial
with a little damp tissue paper to prevent dehydration. If it will be more than
a few hours before the entomologist receives them, they should also be given a
small piece of beef liver. Make sure there is tissue or sawdust present if
liver is added, to prevent drowning. They need some air. Newly emerged maggots
can escape through holes, so a paper towel held over the top of the vial with a
rubber band is excellent, as long as the vial stays upright! (No lid other than
the paper towel is needed).
Eggs are only of value when no maggots or later insect stages are present.
If maggots are already present, don’t worry about the eggs.
If no maggots are present, and the only insect evidence is eggs,
then the eggs are very important and the time they hatch will be vital.
Therefore, observe the live eggs
every few hours and please note time when they first start hatching and the
approximate percentage (e.g. 1015h
10% hatch, 1220 h 50% hatch, 1550 h 100% hatch).
MAGGOTS - collect a range of sizes. Maggots will be found crawling on or near
the remains and may be in maggot masses.
The masses generate a lot of heat, which speeds up development. Therefore,
please note:-
Þ
the
site of maggot masses
Þ
the
temperature of each mass (thermometers can be acquired cheaply at drugstores)
or if no thermometer available, please estimate size of mass.
Þ
label
which maggots come from a particular mass.
Large maggots are usually older so are most important, but smaller maggots may
belong to a different species so both large and smaller maggots should be
collected, with the emphasis on larger maggots.
Collect samples of maggots from different areas of the body and the surrounding
area, and keep them separate.
As mentioned before,
third instar larvae leave the food source to find a suitable area in which to
pupate. They may wander some distance from the body so the soil for a metre or
two around the body should be carefully sifted. Some may burrow down into leaf
litter, so the soil below the corpse should be checked for several centimetres.
If the remains were on a slope, the body fluids will seep downhill and insects
will be found here, feeding on the fluids. This means that a very intensive
search of the corpse, the clothes and the surrounding area must be made in
order to get the entire picture.
When collected, the
sample should be divided into two – half for preservation and half kept alive.
A proportion (approximately half) of
the larvae should be preserved immediately
for two reasons. Firstly, to show the entomologist, if s/he is not present at
the scene, what stage the larvae were when collected, as if they are then
placed on meat, they will continue to develop, giving a misleading impression
to the entomologist when they are examined. Secondly, to produce as evidence in
court.
If there are lots of maggots on the body, preserve approximately half of all
sizes.
If there are only 20-30, preserve 1 or 2
Preserve the specimens by immersing them in hot water for a few minutes, then
putting them in 75-90% alcohol or 50% isopropyl alcohol. If no hot water
available, put straight in alcohol.
DON'T FORGET THAT HALF SHOULD BE KEPT ALIVE. A sample should contain
about 100 maggots (of each size if possible). DO NOT PUT TOO MANY MAGGOTS IN
ONE VIAL – they are air breathers so make sure they are only 1 maggot thick
in the bottom of the vial.
The living specimens should be placed in a vial, with air and food (preferably
beef liver), as for the eggs. There should be only enough maggots to cover the
bottom of the vial. Too many in one vial will drown. A small piece of paper
towel in the vial will help to prevent drowning.
PUPAE and EMPTY PUPAL CASES - these are extremely important and are easy to
miss. They are often found in clothing, hair or soil near the body. Pupae like
dry, secure areas away from the wet food source in which to pupate so pockets,
seams and cuffs are likely hiding places. If the remains are found indoors,
they may have traveled some distance and be under clothing, rugs, boxes etc. They range from 2-20 mm, and are
oval, like a football. They are dark brown when completely tanned. An empty pupal
case is very similar but is open at one end, where the adult fly has emerged.
They need some air, so secure a paper towel over vial as for eggs, as although
the pupae are immobile, if they emerge during transit, an adult can get out of
anything! A piece of tissue in the vial will help to avoid breakage as they are
quite vulnerable. This can be very slightly moistened with water, but be
careful not to drown them. The moisture isn't necessary if the journey is not
long. DO NOT PRESERVE PUPAE! They
won't grow, so the reasons for preserving larvae do not apply, and it is almost
impossible to identify a pupa until it emerges as an adult. I also cannot
determine its exact age until I find out the day on which it emerges. If a pupa
is found when a pale colour, it is just entering pupation, so please keep that
specimen separate and label as pale coloured, as it will darken in a few hours.
Such a specimen can be aged to a matter of hours.
ADULT FLIES - are less important. They are only of use in indicating which species of
insect are likely to develop from the corpse, as you cannot determine whether
an adult has developed on the corpse, or has just arrived from somewhere else
to oviposit, unless it emerged only an hour or so earlier. If an adult has crumpled wings, it may have just emerged, so IS still important as it can be linked
to the body. It should be collected, labeled as such, and kept separate. Adults
can be collected by net or by using an inverted vial. They can be left in the
vial without air or food, as I will kill them as soon as I receive them. The
presence of empty pupal cases, however, indicates that an insect has developed
on the corpse and reached adulthood. This can be very important as it indicates
that at least one generation of flies of this species has completed development
on the corpse.
BEETLES - can be found as adults, larvae or grubs, pupae and also as cast
skins. All stages are equally important. They move fast and are often found
under the body, and in and under clothing. They can be placed in vials with
some air. They are cannibals so should not be placed in the same vial!! It is
often simplest to put the beetles directly into alcohol.
OTHER INSECTS - other insects will be
present, such as cheese skippers. If you are not sure whether it’s an insect,
collect it anyway and place in a vial.
OTHER SAMPLES - Soil and leaf litter samples will also be useful. About half a coffee
can size of soil from under or very
near the body is useful. If the soil below the body is extremely wet, it is
better to collect the soil from near the remains. Half fill the can, leaving
room for some air.
LABELING - Insects collected from one part of the body should be kept separate
from those from another area. Different species should be kept separate as
beetle larvae feed on fly larvae! If they look different, separate them. Each
vial should be labeled with :-
·
area
of body/soil
·
date
and time of collection
·
name
of collector
·
stage e.g. larvae, so that if the specimens
are pupae when I receive them. I will know that they developed into the next
stage during transit.
HANDLING - most specimens are fairly fragile and are probably best picked up
with gloved fingers which are often gentler than forceps if you are not used to
them. Very tiny or delicate specimens can be picked up using an artist's brush
dipped in water or alcohol depending on what you are about to do with them.
Make sure all the vials are very well sealed!
PACKAGING - The insects should be taken
to the entomologist as soon as possible. They should be couriered or hand
delivered to maintain continuity. They should be packaged in a cardboard box as
this has lots of air. Each vial can be taped so that it remains upright. The
whole box must remain upright.
I need to know many other
factors about the death site :-
HABITAT -
general
- is it woods, a beach, a house, a roadside?
vegetation
- trees, grass, bush, shrubs?
soil
type - rocky, sandy, muddy?
weather
- at time of collection, sunny, cloudy?
temperature
and possibly humidity at collection time
elevation
and map coordinates of the death site
is
the site in shade or direct sunlight?
mention
anything unusual, such as whether it's possible that the body may have been
submerged at any time.
REMAINS - I need to know :-
presence,
extent and type of clothing
is
the body buried or covered? if so, how deep and with what (soil, leaves, cloth)
what
is the cause of death, if known? in particular, is there blood at the scene?
or
other body fluids?
are
there any wounds? if so, what kind?
are
drugs likely to be involved? this may affect the decomposition rates
what
position is the body in?
what
direction is the body facing?
what
is the state of decomposition?
is
a maggot mass present? how many? this will affect the temperature on the body
what
is the temperature of the centre of the maggot mass(s)?
is
there any other meat or carrion around that might also attract insects?
is
there a possibility that death did not occur at the present site?
IF THE BODY IS REFRIGERATED AT THE MORGUE before the collection (it
is much better to collect at the scene, but sometimes that is not possible)
then I also need to know the exact time that the body went into the cooler, and
the exact time it came out.
PHOTOGRAPHS, or a video of the
scene, the body in situ and the site
after removal of the body are also extremely useful.
When the insects reach the
insectary, the immature specimens are measured, and examined, then placed in a
jar containing a suitable feeding media. In the case of blowflies, this is
usually beef liver, which is placed on top of sawdust. When the insects reach
the prepupal stage and leave the food source they will burrow into the sawdust
to pupate. The insects are checked daily and when they pupate they are removed
and placed in a petri dish with damp filter paper. The date of pupation and the
date of emergence is noted for each specimen. When the adults emerge, they are
killed and pinned, then placed in an insect box. Each insect has a detailed
label. Any adults collected directly from the corpse are immediately killed and
pinned.
The reasons for raising the
immatures are two-fold. Firstly, larvae are very difficult to identify to
species, but adults have many more diagnostic features. Secondly, the dates of
pupation and emergence are used to help calculate the age at the time of
collection.
Other important information
used to determine elapsed time since death include :-
weather records from the nearest weather station, including temperature and
precipitation
the
distance between the death site and the weather station
This method of determining
elapsed time since death using insect evidence can be demonstrated using an
actual case. Human remains were found in mid October. Most of the head region
was missing as death was due to gunshot wounds. The upper portion of the body
was almost skeletonized, but the lower area, clad in tight clothes, appeared
almost fresh. There were several large maggot masses on the corpse which
generate their own heat for a while due to the frenzied activity. The
temperature of the largest maggot mass was 20oC,
even after the body had been refrigerated at
4oC for two hours. All sizes
of larvae were collected and three pupae. These were pale in colour so had only
just pupated. No puparia were found. The mean temperature at the death site was
15oC.
Two species of blowfly
emerged, Calliphora vomitoria and Phormia regina. Both are common species that are amongst the first
to arrive on a corpse. The oldest stage of
Calliphora vomitoria collected was just entering the prepupal stage of the
third instar. This was determined from size, no. of spiracular slits (breathing
holes) date of pupation and behaviour, in that the largest specimens
immediately left the beef liver and entered the sawdust, indicating that they
had stopped feeding. At the temperature of the deathsite, 15oC, Calliphora vomitoria takes a minimum of 9.3 days to reach the
beginning of the prepupal stage of the third instar. So these insects were a
minimum of 9 days old when collected on 12 October, meaning that they were laid
as eggs on or before 4 October. As there was blood at the scene, the insects
probably arrived very soon after death. Therefore death must have occurred on
or before 4 October.
Using the same techniques
for Phormia regina, the oldest
specimens of which were in the pupal stage when collected, it was calculated
that Phormia regina was oviposited no
later than 3 October. Therefore, using the two insects together, it can be
shown that death occurred on or before 3 October. Other police evidence later
showed that death had actually occurred on 3 October.
OTHER USES FOR INSECTS IN FORENSIC SCIENCE
·
the body may have been moved
after death, from
the scene of the killing to a hiding place. Some of the insects on the body may
be native to the first habitat and not the second. This will show that not only
was the body moved, but it will also give an indication of the type of area
where the murder actually took place.
·
the body may have been
disturbed after death, by the killer returning to the scene of the crime. This may disturb
the insects cycle, and the entomologist may be able to determine not only the date
of death, but also the date of the return of the killer.
·
the presence and position of
wounds, decomposition
may obscure wounds. Insects colonize remains in a specific pattern, usually
laying eggs first in the facial orifices, unless there are wounds, in which
case they will colonize these first, then proceed down the body. If the maggot
activity is centred away from the natural orifices, then it is likely that this
is the site of a wound. For example, maggot activity on the palm of the hands
indicates the probable presence of defense wounds.
·
the presence of drugs can be determined using
insect evidence. There is often not enough flesh left to determine drug
presence, but maggots bioaccumulate so an can be analyzed to determine type of
drug present.
·
insects can be used to place
a suspect at the scene of a crime. For instance, an insect inside a cocklebur was used
to connect a rapist to the rape site.
·
civil cases also sometimes use insect evidence.
·
child or senior
abuse/neglect.
Some insects will colonize wounds or unclean areas on a living person. This is
called cutaneous myiasis. In these cases, the victim is still alive, but maggot
infested. A forensic entomologist will be able to tell when the wound or abuse
occurred. For instance, in the case of neglected children, the onset of maggot
infestation will give a minimum time interval since the child last had a diaper
change. Such cases occur particularly in young children and seniors.
Although forensic entomology
can be very effective in determining elapsed time since death, it has its
limitations :-
1. - The temperature of the death site is obviously a very important factor,
but few criminals are thoughtful enough to kill their victim right underneath a
weather station! In most cases, the weather records come from several miles
away. We are trying to overcome this by setting up a miniature weather station
at the death site after discovery, to compare these data with that from the
weather station, in order to determine the difference between the two sites, if
any. Also the microclimate of the corpse itself will be slightly different from
the surrounding area, especially if a maggot mass is present. Therefore, it is
extremely important to know whether masses are present.
2. - Forensic entomology in Canada
is seasonal, that is, it is only
commonly used in spring, summer, and fall when insects are abundant. It is of
less use in winter, unless its very mild, as there are no or very few insects
present. This can be a limitation, but can also be an advantage as I can sometimes
show that a victim found in spring was killed the previous fall if insect
evidence is present.
3. - The results are not immediate,
as it takes time to rear the insects. DNA evidence is now being developed to
speed up identification of immature specimens.
4. - The body may have been disposed
of in a way that excludes insects e.g.
a) freezing - if the body
was frozen for a period of time before being placed outside on, for example, 8
May, the insects would only invade then, giving the misleading impression that
death had occurred on 8 May. However, other forensic experts would be able to
determine whether or not the body has been frozen, and insect evidence will
still determine time of exposure.
(b) burial - if the body is
buried deeply, then most insects will be excluded. However, most criminal
burials are not very deep, as the aim is merely to conceal the body, and most
insects will dig down to the body, particularly if there is blood soaked in the
soil. Therefore, insect evidence can still be used. We have an estensive
database for buried bodies in B.C.
(c) wrapped - if the body is
wrapped or packaged in some way the insects may be excluded, but the wrapping
must be completely secure. A body part was found sealed in a garbage bag which
had been tied securely at the top, but the remains were maggot-infested, and
showed severe insect damage. The adult females had probably laid their eggs at
the knot, and the minute first instar larvae had crawled in.
5. - More research is needed. Insect succession varies from geographic region
to region and the species and time of colonization must be developed for all
areas using this type of evidence. Research has been conducted in British
Columbia in a variety of habitats, seasons and geographic areas to develop a database
for this Province. Similar databases are presently being developed for Alberta,
Saskatchewan, Manitoba and Nova Scotia.
6. Drugs - the presence of drugs may
affect the development of the insects. Work is planned to determine effects of
common narcotics on insects in Canada
In conclusion, INSECTS ARE EVIDENCE! Forensic
entomology is a very useful method of determining elapsed time since death
after 72 h, and can be used earlier. It is accurate to a day or less, or a
range of days, and may be the only
method available to determine elapsed time since death. I have successfully
defended this evidence in court many times. It is vital that the insects are
collected properly and its accuracy depends on this and on suitable conditions
for insects.
COLLECTION OF INSECT EVIDENCE
DR. GAIL S.
ANDERSON, Forensic Entomologist - contact via
:
Pager - 604
252-5785 (24h), (604) 291-3589 (office) or (604) 856-4058 (home)
Police case
number Date Time
Date found Time found
Location found
Officer in
Charge tel.
Collecting
officer tel.
Weather
conditions at collection time (rain and temp.)
DEATH SCENE
Rural
forest ..........., tillable
field ..........., pasture ..........., brush ..........., roadside
...........,
barren
area ..........., beach ..........., gulley .........., ditch ..........,
(water present?, how much) ..........,
Please
describe
Urban
closed building ...........,
open building ..........., vacant lot ..........., pavement ...........,
trash container
..........., closet ..........., on
carpet ..........., on hard floor ...........,
Please
describe
Aquatic
pond
..........., lake ..........., creek ..........., river ..........., irrigation
canal ...........,
submergence
level ...........,
Ground body
resting on
on
soil directly? ..........., sandy ..........., rocky ..........., muddy
..........., other ...........,
on
vegetation? ..........., describe type and
height
DESCRIPTION OF
REMAINS
clothing
burial? How
deep? what
is covering?
wounds? type where?
Body position
Exposure
full
sunshine partial
sunshine how
long/day? shade
Stage of
decomposition
PHOTOGRAPHS
General scene ..........., habitat surrounding body
..........., body ..........., wounds ...........,
maggots mass (s) ..........., insect activity
..........., ground beneath body after removal ...........,
INSECT
EVIDENCE
Are there any
maggot masses
(very large no. of maggots all together in a ball)?
If so, how
many , where ,
temp. of centre
Description of insect evidence - e.g. maggots, pupae, adult beetles, larval beetles etc.
Samples :- collect from the body
itself, and from the ground (soil or carpet) below and around the body. If on
soil or loose material, the insects may be several centimetres down, and on any
surface may be up to 50-100 cm away from the body. Older maggots will crawl
away from the body to pupate, so may be still maggots, or may be pupae, which
are 5mm-1cm long, red-dark brown, and look somewhat like a chocolate rice
crispy. It is very important to know whether pupae or empty pupal cases are
present and to collect them. They are quite delicate - do not preserve them.
Only preserve maggots. Only some maggots should be preserved, at least half should
be kept alive. Preserve them by immersing in hot water for a few minutes then
putting them in alcohol (90%) if available, or freeze them, if available.
Sample :-
wounds
........., face ........., genitals, if exposed ........., general body
area ........., under body .........,
where
body meets ground ........., clothing ........., in pockets, cuffs etc. .........,
from
soil around body .........., from soil when body removed ...........,
please search soil beneath body for maggots,
beetles, pupae or empty pupal cases.
If remains were refrigerated at morgue, and
collection was performed at autopsy :-
Time and date
body entered the cooler :-
...................................................................
Time and date
body removed from cooler :-
...................................................................
Exhibit no. |
site
collected from i.e. area of body or soil |
Time/date
collected/ preserved |
type e.g. maggots, beetle larvae, flies,
beetles |
Approx.
number maggots preserved - DO NOT KILL PUPAE! |
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Keep maggots and beetles (adult or larvae) separate.
Keep samples from different sites separate.
Put live maggots in vial with very small air-holes,
a piece of paper tissue, and some food, preferably beef liver (about 1 cubic
inch). Only put about 100 large maggots in one container, up to 200 small ones
are O.K.
Signature of
Collector
[1] In its broadest sense, forensic entomology is the study of insects involved in any legal action, and can include urban and stored products entomology.