“The body and the decomposers are telling you what happened,
If you can only understand the language." -Lord and Rodriguez (1989)
Since the inception of human species, man has tried to dominate this planet by sheer intelligence. This dominance led to the concept of noosphere and he started interfering with natural processes. But nature has her own ways and one of its finest intricacies is the food web i.e. the process of eating and being eaten. This cycle is so immaculate that even dead bodies of animals, including that of humans, are decomposed by other creatures with insects playing a predominant role. And who knew that one day these so called natural scavengers would act as witness to man's mud-paddling strategies for personal ambitions, jealousy and gains. Practical use of these organisms in solving crime led to the development of a separate branch of science now-a-days known as Forensic Entomology. Interestingly, when this branch of science was not even thought of, humans did use it as evidence as narrated in a Chinese story (from a 13th century book “Washing Away of Wrongs” translated by McKnight, 1981).
Quote - A worker lay dead in the paddy field, killed by blows from a sickle. The local law enforcement officer went out to where the man has been killed and called together all the field workers in the area. He told them to lay down their sickles in a row on the ground. The weather was hot and it was not long before flies began to congregate on one sickle in particular, probably because of invisible remnants of tissues still adhering to it. At the sight of this evidence the owner of the sickle confessed to the crime - Unquote.
This science emerged as a major discipline with passage of time in the developed countries and its role in criminal investigations became more and more relevant. Nowadays, forensic entomologists are hired by prosecutors and defenders like lawyers. Even some of the well known detective agencies like FBI of USA have employed entomologists as special agents. Hundreds of research papers dealing directly or indirectly with forensic entomology have been published so far and this number is increasing day by day. Four books dealing solely with forensic entomology are now available, namely - “A Manual Of Forensic Entomology” by Smith (1986). “Entomology and Death : A procedural guide” by Catts and Haskell (1990). “A Fly For The Prosecution : How insect evidence helps solve crimes” by Goff (2000) “Forensic Entomology - The utility of arthropods in legal investigations” by Byrd and Castner (2000). Bernard Greenberg, the legendary father of modem forensic entomology is currently writing a monograph on this subject (Personal Communication). The prestigious german research journal, Forensic Science International, is shortly bringing out “Special Issue on Forensic Entomology” that will include research papers by leading forensic entomologists of the world.
With increasing stress on human rights these days, importance of physical evidence in criminal investigations has a major role(Gebereth, 1980a and 1980b; Erzinclioglu, 1983, 1985a; Goff, 1993). Scientific investigations are going to replace the third degree methods all over the world. Insects can act as important forensic indicators in this regard. Even in a developing country like ours, according to the evidence act 138 of Indian Penal Code (IPC), “An evidence is real if supplied by material objects based on scientific documentation.” Undoubtedly insects do fulfill the conditions as laid down in this act. Unfortunately we have not made enough progress in this direction and potentially useful entomological data is going waste in our country. A sound knowledge about carrion fauna of an area is required before this entomological information can be put into practice for criminal investigations. The present proposal “Studies on the Insect Fauna of Decaying Rabbit Carcasses” is a step in this direction.
Forensic entomology proceeds on the common observation that exposed remains present a temporary and progressively changing habitat and food source for a wide variety of organisms ranging from microbes like bacteria and fungi to vertebrate scavengers. Out of these, arthropod fauna comprises a major element of the biota and insects form the most constant, diverse and conspicuous group. These six- legged creatures predominate the terrestrial and fresh water carrion fauna (Payne, 1965). He reported 522 species of animals from decomposing pig carcasses out of which 84% were insects. Goff et al. (1986) while studying carcass decomposition reported 140 arthropod taxa out of which 83% were insects. These insects are attracted in the first instance, to the body fluids oozing from natural openings and to blood or serum escaping from the wounds.
Cadavers are often fiercely contested by great number of insect species. The overwhelming majority are flies and beetles. Dipteran families Calliphoridae, Sarcophagidae, Muscidae, Sepsidae, Sphaeroceridae, Piophilidae and Phoridae and coleopteran families Histeridae, Staphylinidae, Silphidae, Cleridae, Dermestidae and Tenebrionidae predominate the scene (Reed, 1958; Payne, 1965; Braack, 1986; Goff et al., 1986; Goff, 1993; Tantawi et al., 1996). These insects form a complex food web within the carrion. This web gets more complicated because of the fact that many species have different adult food preferences from that of their larvae. Various workers have given different classifications of carrion insects, however, the one given by Smith (1986) has been adopted for the present studies. Accordingly the carrion insects have been grouped into following categories on the basis of their food preferences which obviously reflect their ecological role.
1. Necrophagous Species : These species feed on corpse tissue and are further subdivided into :
(a) Sarcosaprophages : These species feed on decomposing flesh and this group also includes arthropods which imbibe blood or the fluids which bathe the tissues as a thin film (e.g. Calliphoridae, Sarcophagidae, Muscidae, Dermestidae).
(b) Coprophages : Species that are attracted to the rumen contents of herbivorous mammals e.g. Scarabaeidae and Muscidae.
(c) Dermatophages : Species feeding on dried skin, hair, ligament and bones e.g. Dermestidae, Tineidae.
2. Necrophagous - Predaceous Species : Insects that feed on both the corpse and its inhabitants e.g. ants (Formicidae), silphid beetles, clerid beetles and some blow fly larvae.
3. Predaceous Species : Arthropods that feed only on carrion entomofauna, especially dipterous larvae e.g. Histeridae, Staphylinidae.
4. Parasitic Species : Insects that parasitize fly larvae and pupae e.g. endoparasitic wasps.
5. Adventive or Incidental Species : Arthropods that use carrion as a concentrated resource extension of their normal habitat e.g spiders, centipedes, millipedes, mites etc.
Carrion is a specialized ephemeral habitat of tremendous ecological importance. It supports a characteristic assemblage of insects which are attracted to it due to their well developed sense organs. For instance, calliphorids can arrive within few minutes (Payne, 1965; Tullis and Goff, 1987) or even few seconds (DeJong, 1995) following corpse exposure. If given access, the females will oviposit on carrion within first few hours (Hall, 1948; Catts, 1992) or few minutes (DeJong, 1995) after death. These flies have a strong physiological drive to go to their food resource or oviposition site. Norris (1959) trapped Chrysomya rufifacies and other Australian blow fly species four miles from the release points within 24 hours.
The flies and beetles achieve their success in this transient habitat through quite different sets of preadaptations. The dipterans typically have short lived and very mobile adults which are able to search for the suitable habitat over a large area in a short time. The coleopterans are less mobile as adults, but longer lived, and are able to search for much longer time, so that a comparable area can be covered. Coleopteran larvae tend to develop at a slower rate than their dipteran counterparts, but their mouthparts are better adaptable to different kinds of food : an advantage in the rapidly changing conditions within the carrion (Tantawi et al., 1996).
Out of all the insects visiting a dead body the maggots of blow flies (Calliphoridae) and flesh flies (Sarcophagidae) are responsible for the maximum consumption of terrestrial carrion (Fuller, 1934; Payne, 1965; Putman, 1977 and 1978; Braack, 1981; Early and Goff, 1986). Adults of these flies use carrion for feeding, mating and breeding. Blow flies lay eggs while flesh flies deposit larvae in natural body orifices. These larvae quickly invade most of the regions of the animal body (Putman, 1978). The proteolytic enzymes in the larval excreta poured directly into the carrion material further aids in liquefaction of the carcass. The mechanical action of their tunnelling through the tissue increases aeration and helps in dissemination of microorganisms. So both these mechanisms initiated by dipteran larvae serve to increase microbial activity and hasten rate of decomposition. Payne (1965) observed that pig carcasses left uncovered and freely exposed to insects lost upto 90% of their weight within one week during summer month in contrast to screened carcasses made inaccessible to insects which gradually dried out over a period of 100 days.
Sarcosaprophagous fly maggots have high growth rates which enable them to complete their development before the resource vanishes. The amount of metabolic heat generated by large maggot masses in carrion elevates the temperature of the medium above ambient temperature. This speeds up the development of maggots and ameliorates the effect of severe cold climatic conditions (Evans, 1936; Deonier, 1940; Digby, 1955; Kamal, 1958; Payne, 1965; Davison, 1971; Ash and Greenberg, 1975; Vinogradova and Marchenko, 1984; William and Richardson, 1984; Early and Goff, 1986; Nishida et al., 1986; Tullis and Goff, 1987; Greenberg, 1991; Catts, 1992; Catts and Goff, 1992; Turner and Howard, 1992; Tantawi et al., 1996).
During its decomposition and ageing the carrion passes through a series of characteristic physical and chemical changes and in the absence of vertebrate scavengers, a temporal heterotypic succession of arthropod species occurs (Hanski, 1987). While carrion decomposition is a continuous process, many workers have divided it into separate successive stages. Although there is considerable variation in the naming and duration of these stages, yet the general mechanism of decomposition and arthropod succession do not differ greatly. As a rule, 4-5 stages of decomposition are distinguished, though their number may vary from 3 to 8. The idea of using seral stages to identify and delineate temporal patterns in decaying carcasses under rapid invasion and succession by arthropods was first introduced by Megnin (1894) and followed by Johnston and Villeneuve (1897). These early carrion investigations were undertaken to aid forensic pathologists in devising a system to age human cadavers in medicolegal cases. Many subsequent carrion ecologists, in turn followed and expanded this theme, assigning decay stages which corresponded to observed physical and chemical changes in the carcass. They used different animal models ranging from lizards and toads (Cornaby, 1974), Rabbits (Chapman and Sankey, 1954; Mc Kinnerney, 1978; Tantawi et al., 1996) Cats and Dogs (Illingworth, 1926; Reed, 1958; Burger, 1965; Jiron and Cartin, 1981; Early and Goff, 1986), Pigs (Fuller, 1934; Bornemiszza, 1957; Payne, 1965; Payne and King, 1968; Tullis and Goff, 1987; Hewadikaram and Goff, 1991; Shean et al., 1993; Anderson and Van Laerhoven, 1996; Van Laerhoven and Anderson, 1999) and even elephants (Coe, 1978).
Besides their importance in medicolegal applications, well defined decay stages serve to understand the process of decomposition in a better way. These enumerated stages are convenient means of summarizing decompositional patterns and their boundaries are believed to be in close agreement with the changes in arthropod community composition. Thus, the priorities of many carrion researchers have been first to define decay stages and then to describe the carrion arthropod communities in correlation with these stages.
In ecology, succession is defined as the temporal sequence of colonization and species replacement or addition that occurs after a site is disturbed. In the words of Beaver (1984), “Only certain species are able to establish themselves initially. The early occupants modify the unit so that it becomes less suitable for further recruitment of ‘early succession’ species and more suitable for recruitment of ‘late succession’ species.” Most species present during the early stages are specialists in a specific habitat type, and these are mainly the sarcosaprophagous fly larvae. They usually develop rapidly and are present in the community only for a short time. During succession, there is a trend towards more generalized species, able to breed in a wide range of habitats. These generalists are mainly represented by beetles (Coleoptera) present in carrion over a much longer period.
While carrion is often rich in species diversity, only few are true carrion feeders and have a significant role in the decomposition and release of carrion materials. These are mainly the fly maggots and dermested beetles (Putman, 1983). Braack (1987) gave an excellent explanation for this phenomenon. According to him, succession at carrion, to a very large extent, results from the addition, not replacement, of species to the community present at the carcass. The addition of species is due to new resources becoming available as a result of the action of fly maggots within carrion. The emergence of these maggots stimulates the arrival of large numbers of predatory histerid, and staphlinid beetles. The activity of maggots leaves a liquid deposit on the carcass which attracts moisture seeking muscids and other flies. The continued feeding effort of the maggots rapidly exposes the rumen content in initially undamaged carcass which is then utilized by beetles. The departure of maggots creates space for more individuals of species of clerids and dermestids. Hence, a large number of species depend directly on the fly maggots as a food source or indirectly on the influence of maggots on the carcass. The presence of maggots, therefore, and their duration of stay, is a prime factor in determining succession at carcass.”
The science of forensic entomology is based on the analysis of those insects which sequentially colonize a corpse as decomposition progresses and on the rate at which the various stages of their progeny develop. This entomological information can be useful during criminal investigations in order to determine the following :
Time of Death : There are two basic approaches to the application of entomological data for estimating the time of death. During earlier stages of decomposition, the time elapsed since death or postmortem interval (PMI) may be determined by calculating the time required for a given species to reach the particular stage of development recovered from the corpse at the time of discovery. The insects involved in this approach are mostly dipterans, especially those belonging to the families Calliphoridae and Sarcophagidae. The most advanced stage of development which in turn shows the longest period of association with the corpse is used to estimate the minimum possible PMI. After the initial stages of decomposition are over and when the Calliphoridae and Sarcophagidae have departed, estimates are generally based on the interpretations of arthropod succession patterns.
Mode of Death : A dead body having external injuries is more attractive to insects than one having none. So, depending upon the degree of degradation brought about by maggots, an entomologist may be able to suggest the possible mode of death, e.g. strangulation or mutilation (Anderson, 1997). Another application is in the cases where death has occurred due to intake of drugs. A chemical analysis of the maggots found on the dead body can reveal the specific drugs, specially helpful when no human tissues are available for sending to the laboratory for other tests. During experimental studies large number of poisonous chemicals have been recovered from maggots that feed upon animals which died due to intake of such chemicals. To name few, Cocaine (Goff et al., 1989), triazolam, oxazepam, alimemazine, chloripriamine and phenobarbital (Kintz et al., 1990a and 1990b), methamphetamine (Goff et al., 1992), lead arsenate (Leclerq and Valliant, 1992), co-proxamol and amitriptyline (Wilson et al., 1993) have been found to be present in maggot tissues.
Place of Death : The deceased may have been killed at a place other than where the body is found. With knowledge about the carrion fauna of an area and specific habits of species found on the cadaver, an entomologist can help to determine whether the person died at a place other than where the body has been found. Similarly, route of transport of a dead body may also be traced by using entomological data.
There are numerous other special situations where entomologists can help to solve crimes. If a body is found buried in soil, the entomological data can be helpful in determining the period intervening death and burial (Lord et al., 1992). Suspects have been linked to the scene of a crime as a result of them having been bitten by arthropods specific to the vicinity (Catts and Haskell, 1990). Blow fly larvae found in the diapers have been used to provide information on how long children had been neglected by their parents (Lord, 1990).
The above presented text gives a fair idea about the potential importance of this branch of science. However, a detailed knowledge about the carrion fauna with respect to life history, habits, geographical distribution, taxonomy, morphology of immature stages, ecological relations etc. is a must for the use of these insects in solving crime.