Beetles and Other Insects of Forensic Importance

The family Dermestidae contains about 1,000 species worldwide. Adult beetles are oval, 2-10 mm, often covered in patterns of pale and dark scales or hairs that serve as a first identification character. Larvae are more diagnostic: densely hairy, often with a tuft of long setae at the posterior end, and clearly segmented. The larval setae are distinctive enough to survive in archaeological remains and can be recovered from skeletal material centuries after death.

The genus Dermestes includes several species of direct forensic relevance. Dermestes maculatus (hide beetle) and Dermestes frischii are common in warmer climates and arrive once remains begin to dry. Dermestes lardarius (larder beetle) is a cooler-climate species, found in Europe and North America, and is particularly associated with indoor scenes including stored food and museum specimens.

The characteristic damage pattern of Dermestid larvae, irregular feeding holes in skin and dried muscle, often with burrows under the skin surface and exit holes in adjacent surfaces where larvae wandered to pupate, can help identify the level of activity even when larvae themselves are not present. Published developmental data for temperature-dependent growth in D. maculatus allows a minimum time estimate from larval stage and size, though the precision is lower than for blow flies because the developmental base temperature and ADD thresholds are less comprehensively validated across geographic populations.

• Dermestes maculatus: worldwide in warm climates; adults 5-9 mm, dark with pale lateral patches; larvae orange-brown with long paired posterior setae; feeds on dry skin, muscle, and bone marrow.
• Dermestes lardarius: cooler climates; black with pale anterior band on elytra; more common in indoor or cool outdoor scenes; also found on stored meat, cheese, and museum collections.
• Attagenus species (carpet beetles): smaller than Dermestes, common in indoor scenes; feed on fabrics, hair, and dried organic matter; their presence at an indoor death scene can indicate the chronological stage of desiccation.

Silphidae are among the largest and most conspicuous beetles recorded at decomposing remains. Adults of Nicrophorus (burying beetles) are 15-35 mm, black with orange-yellow markings, and are immediately recognisable. They carry gamasid mites phoretically and arrive within hours to days of death. On small carcasses, a pair of adults will actively excavate soil beneath the body to bury it and form a brood ball on which they lay eggs. For large human remains, they cannot complete burial, but their presence still indicates freshness of the remains and can contribute to scene reconstruction.

The genus Silpha includes flattened, dark beetles that feed directly on moist tissue during active decay. Silpha obscura and Silpha atrata are common in European cases. Unlike Nicrophorus, they do not bury remains and are purely scavengers. Their larvae also feed on soft tissue and are sometimes confused with fly larvae at first glance, but beetle larvae have clearly defined legs, which dipteran larvae lack.

Rove beetles (Staphylinidae) are the most species-rich beetle family on Earth (over 60,000 described species) and are present at most outdoor decomposition scenes from relatively early in the process. Their defining character is the drastically shortened elytra, leaving most of the flexible abdomen exposed. At a carrion scene, staphylinids serve multiple roles: some species feed directly on moist tissue in the bloat and active decay stages; many others are predatory on fly larvae.

Genera commonly recorded at human remains include Creophilus (very large, hairy, predatory), Ontholestes, and Philonthus among others. Their succession timing is less well characterised than Calliphoridae or Dermestidae, but their presence during active decay is useful corroborative evidence.

Cleridae (checkered beetles) arrive at remains specifically to predate other insects, primarily fly larvae. They are small to medium-sized (3-24 mm), often brightly patterned, and their presence at a scene tells the entomologist that fly larvae were abundant enough to support a secondary predator. The North American species Necrobia rufipes (red-legged ham beetle) has some of the best-documented developmental data among coleopteran forensic indicators and has been proposed as a PMI tool for remains in the late decay stage.

Mites are arachnids (class Arachnida, order Acari), not insects, but they are included in the forensic entomologist's scope in most jurisdictions. Two groups are particularly significant: gamasid mites (suborder Gamasida, sometimes called mesostigmatid mites) and astigmatan mites (suborder Astigmata, including the families Acaridae and Glycyphagidae).

Gamasid mites use phoresy on flies and burying beetles to disperse to fresh resources. When a blow fly puparium is cut open, it often contains multiple mites that travelled on the emerging adult. These mites can be identified to species by specialist acarologists and their species composition provides information about the geographic origin of colonisation and the environmental context of decomposition.

Astigmatan mites colonise remains in large numbers at certain stages, particularly on wet, fermenting material during active decay and in the greasy residues of advanced decay. Some species, particularly in the genus Acarus and related genera, produce a dispersal stage (the hypopus) that can survive adverse conditions in diapause and resume development later. The presence of hypopi in soil beneath remains long after skeletonisation is a record of historical activity.

Lepidoptera (moths) are not primary carrion insects in the open environment, but they become significant in enclosed indoor scenes where fly access was restricted and in buried or mummified remains. The families most often encountered are Tineidae (clothes moths) and Pyralidae (a large family that includes stored-product moths).

Tineid larvae construct characteristic silken galleries or portable cases as they feed. Finding these structures in the hair, clothing, or dry skin of remains is evidence that the area was dry enough and undisturbed long enough for moth larvae to complete at least part of their development. Tinea pellionella (case-bearing clothes moth) and Tineola bisselliella (common clothes moth) are the species most commonly encountered, both cosmopolitan.

A case from the historical forensic entomology literature illustrates the point: K.G.V. Smith (1986) documented a case involving skeletal remains in a sealed attic where clothes moth larvae provided the only insect evidence, and their life stage was consistent with a minimum desiccation period of several months. The moths had colonised clothing on the body after the soft tissue was consumed by earlier insects or had desiccated.

Beetles are collected using aspirators, forceps, and pitfall traps placed around the body perimeter. Adults are preserved in 70-80% ethanol for identification. If rearing to adult is needed (e.g., for dermestid larvae found at a scene), larvae are placed in a container with a dried meat or skin substrate, held at a controlled temperature, and monitored daily. Adult emergence timing provides additional developmental data for the case.

Soil sampling beneath the body and at a control location one metre away should always be taken for mite extraction. The standard volume is 250-500 ml per sample. Mites are extracted by Berlese funnel (a funnel with a heat source above and a collecting vial below) within 24 hours of collection, before the soil dries. Preserved mites require a specialist to identify, but the extraction and preservation are within the forensic entomologist's scope.

• Adult beetles: ethanol preservation or dry-pinning after ethanol kill; note collection site, body position, and date.
• Beetle larvae: boiling water kill then ethanol, same as fly larvae; keep rearing subsample alive.
• Mites: Berlese extraction from soil within 24 hours; preserve in 70% ethanol; label with case number and GPS coordinates.
• Moth larvae and cases: photograph in situ, then transfer to a sealed container. Note the substrate (hair, fabric) and degree of feeding damage.