Forensic Insects of Skeleton Acres

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1 Forensic Insects of Skeleton Acres PREPARATION: Read: Michaud, et al Natural and anthropogenic changes in the insect fauna associated with carcasses in the North American Maritime lowlands. Forensic Sci. Int. Read: Watson, E.J Faunal succession of necrophilous insects associated with high-profile wildlife carcasses in Louisiana, Chapter 1 (pp. 1-22). Louisiana State University Dissertation. Read about the Shannon-Wiener Diversity Index at: Learn about forensic entomology: View the video Crime 360: Forensic Tools: Forensic Entomology : MATERIALS: 50 transect tape 10 pitfall traps, carrion, flags, moist sand Datasheets 5 containers for pitfall trap samples (with preservative) 10 collecting vials for flies Tray for sorting, long forceps, hand lenses GOAL: Comparison of the composition of the carrion-feeding beetle guild along a creek bed versus on the prairie. RATIONALE: Data relating directly to successional patterns, development rates, and species composition of necrophilous insects on wildlife carcasses in Kansas are limited, unpublished, or lacking entirely. The Department of Anthropology at Wichita State University uses Skeleton Acres to study forensic anthropology. Data collected will help to address our gap of knowledge related to insect forensics. BACKGROUND: In the last two decades, the incorporation of entomological research has become extremely valuable in determining the postmortem interval (PMI) of homicides, suicides, and other unattended deaths. The same entomological criteria used to estimate time of death of humans are also applicable for determining PMI of animal carcasses with the purposes of providing valuable information to law enforcement with the goal of incriminating poachers. Necrophilous (i.e., carrion - frequenting) insects are little studied within forensic science. There is a great deal of regional variability due to species compositions, habitat composition, and weather variables. More data are necessary for more reliable use of insects in forensic science. Many insects make their living on carrion they are the garbagemen of the natural world. Without these insects, our world would be littered with dead and decaying animals. They break-down dead animals into their constituent parts and recycle them. Carrion insects are useful in human homicide cases because they assist in determining the PMI, place of death, and if the body has been moved. Insects are equally important in PMI of poached animal carcasses. Competition at a carcass is fierce, so insects arrive as soon as putrification begins. Early arrivals at a carcass tend to be beetles that specialize in carrion or those that feed on fly larvae. These include the carrion beetles (Silphidae; larvae feed exclusively on carrion) as well as hister beetles (Histeridae) and rove beetles (Staphylinidae) whose adults feed on fly larvae, pupae, and eggs. Dung beetles (Scarabaeidae) are attracted to large carcasses, especially to the intestine of herbivorous mammals. Late-arriving species tend to be specialist scavengers that feed on tougher parts like skin and tendons as the body dries out. The dominant late stage scavengers include hide beetles (Dermestidae) and skin beetles (Trogidae). Trogids and dermestids have enzymes necessary for breaking down keratin, a protein component of hair and fingernails. We will use the Shannon-Wiener Diversity index to compare the diversity between two communities at Skeleton Acres. Unlike a rapid assessment technique (like the Index of Biotic Integrity), diversity indices record more accurate point data. Data are more easily pooled and experiments are more easily repeatable. Studies set up to calculate diversity indices are, however, more time intensive. The Shannon-Wiener Diversity Index (H) is used in biology and ecology. It measures the rarity and commonness of species in a community. H values are compared, and the higher number indicates a higher community diversity. Related indices include Richness (S) (the total number of species in the community) and Evenness (E) (the measure of relative abundance of different species in an area). The Simpson Diversity Index (D): D = S p i 2 computes richness. Evenness is computed as follows (E): E = H / ln( S ). 1

2 PROCEDURE: Two transect lines in each habitat (creek bed and the prairie) have been installed at Skeleton Acres. Each transect line has pitfall traps that are placed 15 m apart. The pitfall trap consists of 0.5 l container buried in the ground so that the top of the container is level with surface of the ground. About 4 oz. moist sand was placed in bottom of container. The trap is baited with one dead mouse. Chicken wire placed over top of trap and staked in four corners. Each trap is marked with a flag. Work in teams of five. Team leaders should assign one person to record GPS locations for each trap and take a digital image of the habitat (see #2); one person to sweep traps for flies and collect flies (see #2); two people to sort and identify contents of the trap (see #3); and one person to record the species and abundance data collected from the trap (see #3-4).One group of students will gather data at the prairie transect and the other will gather data at the creek bed transect. At each transect, each group will perform the following: 1. Record habitat and weather data prior to examining contents of the traps. These data can be supplemented with climatic data from the Kansas Office of State Climatology for the duration of each study. If you were recording data for a human or wildlife carcass, documentation on the internal temperature (core temperature) would be required using a 12.7 cm stem metal thermometer inserted deep into the ribcage. Carcass temperature, including the generated maggot mass heat, should be recorded until skeletonization occurs. 2. Check each trap. At each trap, record the GPS latitude and longitude and take a digital image of the surrounding habitat. On first approach to the trap, perform an aerial sweep to collect adult flies above the trap. Place the fly specimens in a collecting container and label it according to the trap number and transect. The trap number should be include transect line (prairie PR ; creek CR ), trap number (1-5), and date. An example is: PR-3-VII (= Prairie transect, trap #3, July 21, 2011). 3. Examine the trap. Remove the trap and remove the larger insects first. Record the number of individuals of each species on the datasheet. Use the guide to identify species or the lowest taxonomic group possible. Record abundance and species for carrion beetles (Silphidae), dung beetles (Scarabaeidae), skin beetles (Trogidae), rove beetles (Staphylinidae), hister beetles (Histeridae), and hide beetles (Dermestidae). After the larger insects are removed and placed in the labeled collecting container, then dump the contents of the trap on the sorting tray. Record abundance and species for these individuals as well, then place specimens in the labeled collecting container. Identify the species and record the number for each trap. 4. After you have satisfactorially identified and collected all specimens in the trap, invert the trap so that no further insects can be trapped in it. Leave the flag and the trap in their location for future research. 5. Identification for most of these insect groups requires dissection of internal characters. Keys for species in some groups are not available to species (e.g., some genera of Staphylinidae), thus only the genus will be recorded. Voucher specimens will be placed in the WSU Biological Field Station insect collection. All specimens will be identified and curated to establish a reference collection. The reference collection will provide the basis for which a diagnostic tool will be established as well as to confirm identification and repeatability. These research tasks will not be the responsibility of the group during the lab exercise. If you wish to learn more about these processes, please talk with me. If you were collecting data for a forensics case, other data that would be important include: 1) Exposure of the carcass (open air, burial/depth, clothing entire or partial, nude (portion of body), description of clothing, type of debris on body) 2) Stage of decomposition (fresh, bloated, active decay, advanced decay, saponification, mummification) 3) Dismemberment 4) Evidence of scavengers 5) Possible traumatic injury sites 2

3 Forensic Insects Guide (Beetles) Silphidae: Carrion beetles Left to right: Necrodes surinamensis, Necrophila americana, Nicrophorus orbicollis, Nicrophorus tomentosus, Oiceoptoma novaboracense Silphid beetles are scavengers of carrion. About 20 different species of silphids occur in Kansas. The genus Nicrophorus buries carrion thus preventing infestation by flies. The endangered American Burying Beetle is a member of the Silphidae. This species historically occurred in Kansas as far west as Wichita, and populations recently have been recorded in the southeastern counties of the state. Extant populations of this endangered species are widely scattered and may be associated with pristine habitats. The decline of the American Burying Beetle may be associated with the extinction of the passenger pigeon. Adults provide parental care to their larvae, something that is unusual among the insects. Keys are available to all American species. Scarabaeidae: Dung Beetles Left to right: Phaneus vindex, Onthophagus species, Canthon pilularius, Copris species The World dung beetle fauna includes slightly over 5,000 described species in 234 genera, with close to 1,800 of these species belonging to the genus Onthophagus. Although many species feed on mammalian dung, others specialize to varying degrees upon the dung of other vertebrates and invertebrates, as well as on carrion, mushrooms, rotting fruit, and other decomposing plant material. Adults of some species are ball-rollers, and they shape carrion or dung into balls that are rolled away and buried at a distance from the food source. Keys to species are available for all American species. 3

4 Staphylinidae: Rove Beetles Left to right: Pederus species, Emus species, Ocypus species, Platydracus species Staphylinidae is the second largest family of beetles, with over 45,000 species known worldwide. The rove beetles are primarily distinguished by their shortened elytra (that leave more than half of the abdomen exposed) and their slender body. Rove beetles are known from every type of habitat, and their diets include everything except the living tissues of angiosperm plants. Many rove beetles live in leaf litter and decaying plant matter where they are predators of insects and other invertebrates. Several species have adapted to live as inquilines in ant and termite colonies, and some have a symbiotic relationship with mammals whereby they eat fleas and other parasites on the mammal, thus benefiting the host. The very large genus Aleochara includes species that are parasitoids of other insects, particularly of certain fly pupae. Adults of Platydracus occur in carrion and eat fly larvae and adults. Keys to genera are available for American rove beetles; keys to species may not be available. Trogidae: Skin Beetles Left to right: Trox species, Omorgus species The Trogidae is a small family (about 300 species worldwide) that occurs on all major continents. Adults and larvae can be found on the dry remains of dead animals (they are usually among the last of the succession of insects that invade carcasses) or in the nests of birds and mammals where they feed on hair, feathers, and skin. When disturbed or frightened, adults feign death and remain motionless. This, in combination with their dirtencrusted appearance, enables them to evade potential predators that might be scavenging at a carcass. Adults stridulate by rubbing a plectrum (located on the penultimate abdominal segment) against a file (located on the internal margin of the elytra). Keys to genera and species are available for American skin beetles. 4

5 Histeridae: Hister Beetles Left to right: Hister species, Geomysaprinus goffi The beetle family Histeridae is a relatively small beetle group that includes 3900 species in about 330 genera worldwide. Most species are predaceous, and they are often found on dung and carrion where they feed on fly pupae and larvae. Histerids are typically ovoid, shiny, and black or metallic green. Many species are associated with dead or dying trees or other decomposing vegetable matter. Some histerids live in vertebrate nests and burrows, and many species in the colonies of social insects. Dermestidae: Hide Beetles Left to right: Attagenus species, Larval & adult dermestids Dermestid beetles feed on a wide variety of organic matter including fresh and dried foods (they are probably in your kitchen cupboards!), woolen and silk products, rugs, museum specimens, pollen, and the dried remains of carcasses. Larvae are covered with long hairs (called setae). The family includes less than 1000 species world wide. Due to the economic importance of the group, keys are available for American genera and species. 5

6 RESULTS (to be completed by the Research Presenters): Using the data collected, calculate the Shannon-Weiner diversity index for each transect. The on-line calculator ( uses the following formula to calculate the Shannon-Wiener diversity index: H = - S p i ln ( p i ) Here p i is the proportion of total number of species made up of the i-th species. Input the numbers from one trap in the window, indicate that you have one dataset, then click on Diversity Calculator. Do this for each transect, then provide an analysis of the results. Another on-line calculator can be found at: Additionally, it is fairly easy to create a Shannon-Wiener calculator in excel (see DISCUSSION AND SIGNIFICANCE: Research Presenters should consider the following discussion questions. Prairie Transect: Comment on the following: Do you think that results for the creek bed transect will be very similar to those of the prairie? If not, why might they differ? If we examined succession instead of diversity, how might succession differ between habitats? Discuss the limitations of the study. For example, did the sampling method represent all of the insects? Creek Bed: Comment on the following: Do you think that results for the prairie transect will be very similar to those of the creek bed? If not, why might they differ? If we examined succession instead of diversity, how might succession differ between habitats? Discuss the limitations of the study. For example, did the sampling method represent all of the insects? ASSIGNMENT: Turn in data sheets. Be certain that you have completed all data fields and that you include your name and your role ( GPS recorder and digital image taker, Fly collector, identifier and sorter, species ID and abundance recorder ). Read field laboratory for the next class, and bring the materials listed in the Materials section. 6