Maggots
When a dead body is exposed in nature it soon becomes attractive to other forms of life.
Carnivorous animals will come to eat; insects will arrive to lay their eggs; crows, rats and mice may
come to peck or nibble at the remains. All this may sound macabre, but it is a fact of life; moreover,
it is a fact that can enable us to estimate the time of death.
Flies of one kind or another are usually the first to arrive at a dead body. Such a body,
exposed above ground during the warmer months of the year, will attract bluebottles and
greenbottles. The flies will lay their eggs in the natural body orifices (ears, nose, eyes, etc.) and the
maggots that eventually} hatch will feed on the muscle tissues of the remains. They will grow, shed
their skins, feed a bit more, shed their skins again, then feed and grow until they have extracted
enough nutrient: from the body to enable them to pupate. The last maggot stage will then leave the
body, burrow in the soil (or crawl under an object, such as a carpet, if indoors) and pupate. Its outer
skin becomes hard and it darkens and contracts, forming the pupa case, or puparium. Eventually,
the adult fly will emerge from j case and the cycle will start all over again.
As it happens, maggots of various kinds are very intensively studied creatures, not only
because of their forensic interest, but also for their relevance to medical and veterinary problems an
for the simple fact that, being easy to keep in laboratory color they are used for studies on
development and genetics. This knowledge is put to good use in forensic investigations.
The basic question that a maggot can help us to answer is this: "What is the minimum time
that has elapsed since death?" In other words, what is the time after which death could not have
occurred? For example, if we can estimate the age of a maggot being, say, five days old, then we
can say that death could not have happened later than five days before discovery of the body.
Knowing the age of the maggot cannot tell us the actual date of death, since we do not know when
the fly arrived at the body, only the minimum time that must have passed since the crime was
committed.
If we have reason to believe that the body had been exposed fly activity almost as soon as it
was dead, then we can say that the minimum time since death is the actual time of death. The
ability of flies to detect the odour of a dead body, even at the very earliest stages, is so well
developed that they will reach it well within an hour after death.
How does one determine the age of a maggot? Like all living things, with the exception of
birds and mammals, the rate of development of maggots is determined by the external temperature,
since they cannot control their body temperature internal physiological mechanisms, as we can.
Therefore, in on to estimate a maggot's age one has to have a very good idea of the temperatures
that prevailed during the course of its development. "So, one needs to take the temperature of the
maggots in the body, which can be many degrees above the surrounding temperature, adding
another complication to the estimation of time of death based on body cooling. In some cases, he
air temperature may be of the order of 20°C, whereas the maggot-infested body may have a
temperature as high as 40°C.
While it is an easy matter to measure the temperature of the maggots and the surrounding
air at the scene, it is much more difficult to estimate the temperatures that prevailed in the days
before the body was discovered. Consequently, one has to find another source of information,
which is provided by the meteorological offices. Unfortunately, this is only the beginning of the
solution.
As we have seen, it is important to make at least two sets of temperature measurements at
the scene, in order to establish the relationship between them. Despite the fact that we know a
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