Necrodes littoralis | |
---|---|
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Class: | Insecta |
Order: | Coleoptera |
Family: | Silphidae |
Genus: | Necrodes |
Species: | N. littoralis |
Binomial name | |
Necrodes littoralis (Linnaeus, 1758) | |
Synonyms [1] | |
Silpha littoralisLinnaeus, 1758 |
Necrodes littoralis, also known as the short sexton beetle, [2] is a species of carrion beetle of the genus Necrodes , found in countries across Europe. As a carrion beetle, it feeds on decaying vertebrate remains and maggots. This species' feeding behaviors make it an important asset to forensic entomology.
Adults of N. littoralis grow to be 15 to 25 mm (0.59 to 0.98 in) long and have a shiny black body. The beetles can be identified by a characteristic bump about three quarters down the length of their elytra, a hardened forewing that act as armor to protect the beetle from environmental factors and predators. [2] Beetles of the order Coleoptera, like N. littoralis, have truncated elytra. The reason why some beetle species have adapted a shortened protection armor is unclear. [3] The larvae of N. littoralis are campodeiform, meaning they have a flattened body, antennae, and have well-developed legs. [4]
N. littoralis has a Palearctic distribution, but most observations are reported across Europe. [5] [6] [7] They have been observed in Austria, Hungary, Slovakia, Czech Republic, Belgium, France, and England. [2] Outside of Europe, N. littoralis has been observed in South Korea. [5]
The Latin prefix necr- denotes corpse, and the Latin word littoralis denotes a coastal environment, which can be misleading given that the beetles are not found solely by the coast. [8] [9] In fact, the beetles are mostly seen in woody areas or fields. [2]
Adult beetles and larvae are primarily found on large carrion in the late stages of decomposition. Further, the carrion is primarily found outdoors. However, there have been observations of N.littoralis on carrion that are indoors. Researchers hypothesize that the beetles have difficulty accessing decaying bodies indoors as they cannot easily detect openings in buildings. [2]
Researchers from Italy reported the presence of N. littoralis on a human corpse in Italy for the first time in 2021. [5] The decomposition conditions of the corpse at the time of discovery align with the consensus that the beetles inhabit corpses at later stages of decomposition. The corpse was found indoors, which the researchers explain that "the access to the building through the open door and the state of total neglect of the area where the corpse was found ... may have favored the indoor colonization by N. littoralis." [5]
Studies were conducted to elucidate the benefits of the aggregation behavior adopted by N. littoralis. Data on mortality, rate of growth, size was collected to for adults raised individually and compared to results obtained from beetles reared in aggregations. Scientists discovered that aggregations amongst larvae especially led to decreased development time, reduced mortality, and these beetles even grew to be larger. Temperature was a confounding variable that influenced these results as well. Lower temperatures of approximately 16 °C (61 °F) was the ideal condition to observe the greatest results from aggregative behavior. Larvae adjust for fluctuations in temperature by moving to other locations or raising the temperature within feeding aggregations. Group living has its benefits for these beetles because it makes foraging easier and creates a stronger defense against predators. These behaviors are important to understand because they impact N. littoralis's capacity to survival and develop. [10]
Mating of adult beetles typically occurs at night. [6] Following mating, the female lays eggs in the ground near the carrion. [2] Although there is variation in the exact number, females lay between 50 and 70 eggs at a time. [6] Researchers who studied the instar development of N. littorialis explain that the beetles have three larval stages. Another study reveals that the three larval stages are first instar, second instar, and third instar. [11]
Post-feeding larva, nymph, and imago are parts of the developmental stage of larvae into adult beetles. [11] The first instar larvae are creamy white when they hatch and shift toward the carrion for food. First instar larvae are the most vulnerable. The second and third instar larvae are also creamy white after ecdysis, which is the process of insects shedding their exoskeleton. [6] [12] [13] As part of the transition from third star larvae to post-feeding larvae, the third star larvae burrow into the ground and form pupal chambers "thrashing the abdomen and thus compacting the soil around them. They go through the prepupal, pupal, and teneral adult stages inside the chambers." [6] The beetles emerge from the pupal chamber after "they become fully sclerotized and colored." [6]
The larvae of N. littoralis aggregate, as they form large and orderly groups of larvae on the carrion. In these large groups, the larvae feed on the carrion. Researchers who are interested in exploring why the beetle larvae group for feeding performed an experiment to test the "importance of thermal cues and ground-deposited chemical cues for the aggregation behavior..." [14] The experiment involved field data and lab tests. The field data consisted of analyzing the larvae growth results of previous experiments with pig carcasses. The lab tests involved collecting adult beetles, allowing one male to mate with one female, allowing the larvae to grow, and placing them on a sample carcass set-up to observe aggregation behavior. [14] The study found that N. littoralis larvae formed aggregations around a heat source of the carrion, which demonstrates the importance of stable thermal conditions for the larval aggregations.
The experiment also found that if the heat source moved, the larvae aggregations followed by disassembling and forming a new aggregation around the new heat source. Stable thermal conditions are important for the development of the larvae into adult beetles. [14] Notably, larvae in the later stages of development, specifically third instar larva, prefer to aggregate in cooler temperatures. The authors hypothesized that this preference allows the larvae to grow larger, though this growth happens more slowly. The third instar larva phase begins the transition to the post-feeding phase, which is when the largest larvae were observed in another study. [6] [14] Additionally, the aggregations form around parts of the carrion that are favorable for feeding. The data from the experiments did not support the ground-deposited chemical cues as an important motivation for aggregation behavior. [14]
Adult N. littoralis are most active during the spring and summer months. [2] [14] Adult beetles on carrion feed on the decaying tissues, but mostly consume Diptera larvae, which is the larvae of flies, especially blow flies. [2] [7]
Adult N. littoralis are hypothesized to perform indirect parental care for their larvae by spreading "anal exudates" on the carrion, which produces heat on the carrion and helps direct the location of larvae aggregation to an area with suitable temperatures. [15]
Necrodes littoralis and other necrophages are attracted to carrions by cadaveric volatile organic compounds (VOCs), which are gases emitted into the air by the carrion. [2] [7] Minimal information is known about the VOCs of cadavers at late stages of decomposition that attract beetles like N. littoralis.
To find out about the VOCs that attract N. littoralis, researchers tested the response of the beetles to different VOCs. The VOCs tested were "benzyl butyrate, butan-1-ol, butyric acid, cadaverine, dimethyl disulfide, dimethyl trisulfide, indole, phenol, putrescine and skatole" [7] The list of VOCs tested included VOCs released in the late decomposition stages to account for the beetle's timing of habitation. The study found that there was not a positive and significant attraction of N. littoralis to the listed VOCs. The main limitation of the study was the low quantity of VOCs and replicates used in the experiment. Ultimately, this study did not resolve the mystery of which VOCs N. littoralis are attracted to. However, the researchers did observe that adult beetles began to inhabit the carrion around the time the carrion started bloating. Bloating of a carrion results from accumulation of gases released by decomposition. The researchers explain that future studies should focus on identifying the gases that cause bloating to narrow down the possible VOCs that attract N. littoralis to carrions. [7]
N. littoralis are not the only insects that inhabit large carrion. The other most common inhabitant of carrion is flies, specifically blow flies (Calliphoridae). [16] It is understood that both beetles and blowflies help decompose bodies, but researchers in Poland were interested in the competitive aspect of the N. littoralis and blow fly interactions and thus conducted a study to investigate this. [16] Blow flies inhabit the carrion soon after death whereas the beetles inhabit the carrion much later after death, closer to the time of the body bloating. [7] [16]
Despite these timing differences, the two insects share similarities in their interactions with the carrion. For example, larvae of both insects form aggregations while they feed on the carrion. The authors of the previously mentioned study explain that "similarities in carrion utilization prompted us to hypothesize that blow flies and Necrodes beetles compete over large carrion." [16] The authors hypothesized that the blow flies would have access to the best territory on the carrion since they arrive first and the beetles would choose the remaining available areas of the carrion. This hypothesis was tested by evaluating experiment results of a previous study involving pig carcasses.
Another hypothesis proposed by the authors of the aforementioned study was that the beetles "compete with blow flies by killing the larvae that are prior on in their peak feeding phase [...] These predictions were tested in behavioral laboratory assays." [16] The primary result of the study was that the blow flies and the beetles have a competitive relationship. This was made evident by the observation that flies reduce the available area of feeding on the carrion for the beetles, which is an indirect effect on the beetles, and that the beetles directly affect the flies by consuming the fly larvae. Interestingly, the beetles kill the fly larvae that are the youngest and smallest, indicating that consuming fly larvae is not a strategy to eat more food, but a strategy to reduce the competition over the carrion. [16]
N. littoralis are useful forensic entomologists as analysis of their behaviors and growth can reveal evidence in death cases. [6] Post-mortem interval (PMI) is a measurement used to identify how long a body has been dead. PMI can be determined by creating a developmental model of the activity of carrion beetles, like N. littoralis. Researchers conducted a study comparing individual rearing vs. aggregation rearing of N. littoralis to develop a standardized approach to PMI estimation. [10] The results of the study indicate that beetles reared individually have a higher mortality, take more time to develop and are smaller in size. On the other hand, beetles reared in aggregation have lower mortality, take less time to develop, and are larger in size. The authors suggest that for forensic entomologists to get more precise PMI results from modeling the beetle's activities, it is best to create a model that rears the beetles in aggregation. [10]
N. littoralis have a preference for outdoors and decomposed cadavers. In a study investigating French forensic entomology cases involving the species, it was found that N. littoralis is primarily found on cadavers that are in "advanced decomposition". [2] They are also frequently found on cadavers that are in "early decomposition", but are rarely found on cadavers that fresh. As a result of these preferences by the species, N. littoralis is uncommonly found in forensic entomology cases, since human cadavers are typically found early before advanced decomposition can occur and are also not commonly located outdoors. [2]
N. littoralis also have a seasonal association with forensic entomology cases. In the previously mentioned study, it was found that most of the cases involving the species occurred in the months of June, July, August, and September. [2] In the area of France, these months are typically dry and hot, demonstrating a preference of the species for these conditions. [2]
N. littoralis adults discovered on a human corpse in Italy were studied in experiments. It was revealed that N. littoralis can be retrieved from carcasses from the time frame of March to May. As the carcass decayed, adults appeared 11 days after its positioning and larvae emerged after 25 days. This species displays intense competitive and predatory behavior, toppling insect hierarchies and dominating the decay stage. Olfactometric studies were used to unveil that these beetles are attracted to the sulphur containing compounds that are released by carcasses during their decay. These compounds work in conjugation with other signaling molecules to attract N. littoralis adults and larvae. Carcasses were often a resource utilized by adults for breeding and the growth and development of their larvae. [17]
Forensic entomology is an science study of colonization of a dead body by arthropods. This includes the study of insect types commonly associated with cadavers, their respective life cycles, their ecological presences in a given environment, as well as the changes in insect assemblage with the progression of decomposition. Insect succession patterns are identified based on the time a given species of insect spends in a given developmental stage, and how many generations have been produced since the insects introduction to a given food source. Insect development alongside environmental data such as temperature and vapor density, can be used to estimate the time since death, due to the fact that flying insects are attracted to a body immediately after death. The identification of postmortem interval to aid in death investigations is the primary scope of this scientific field. However, forensic entomology is not limited to homicides, it has also been used in cases of neglect and abuse, in toxicology contexts to detect the presence of drugs, and in dry shelf food contamination incidents. Equally, insect assemblages present on a body, can be used to approximate a given location, as certain insects may be unique to certain areas. Therefore, forensic entomology can be divided into three subfields: urban, stored-product and medico-legal/medico-criminal entomology.
Silphidae is a family of beetles that are known commonly as large carrion beetles, carrion beetles or burying beetles. There are two subfamilies: Silphinae and Nicrophorinae. Members of Nicrophorinae are sometimes known as burying beetles or sexton beetles. The number of species is relatively small, at around two hundred. They are more diverse in the temperate region although a few tropical endemics are known. Both subfamilies feed on decaying organic matter such as dead animals. The subfamilies differ in which uses parental care and which types of carcasses they prefer. Silphidae are considered to be of importance to forensic entomologists because when they are found on a decaying body they are used to help estimate a post-mortem interval.
Histeridae is a family of beetles commonly known as clown beetles or hister beetles. This very diverse group of beetles contains 3,900 species found worldwide. They can be easily identified by their shortened elytra that leaves two of the seven tergites exposed, and their geniculate (elbowed) antennae with clubbed ends. These predatory feeders are most active at night and will fake death if they feel threatened. This family of beetles will occupy almost any kind of niche throughout the world. Hister beetles have proved useful during forensic investigations to help in time of death estimation. Also, certain species are used in the control of livestock pests that infest dung and to control houseflies. Because they are predacious and will even eat other hister beetles, they must be isolated when collected.
The common green bottle fly is a blowfly found in most areas of the world and is the most well-known of the numerous green bottle fly species. Its body is 10–14 mm (0.39–0.55 in) in length – slightly larger than a house fly – and has brilliant, metallic, blue-green or golden coloration with black markings. It has short, sparse, black bristles (setae) and three cross-grooves on the thorax. The wings are clear with light brown veins, and the legs and antennae are black. The larvae of the fly may be used for maggot therapy, are commonly used in forensic entomology, and can be the cause of myiasis in livestock and pets. The common green bottle fly emerges in the spring for mating.
Cynomya mortuorum belongs to the order Diptera, sometimes referred to as "true flies". In English, the only common name occasionally used is "fly of the dead". It has a bluish-green appearance, similar to other Calliphoridae and is found in multiple geographic locations with a preference for colder regions. Belonging to the family Calliphoridae, it has been shown to have forensically relevant implications due to its appearance on carrion. Current research is being done to determine C. mortuorum's level of importance and usage within forensic entomology.
Calliphora vomitoria, known as the blue bottle fly, orange-bearded blue bottle, or bottlebee, is a species of blow fly, a species in the family Calliphoridae. Calliphora vomitoria is the type species of the genus Calliphora. It is common throughout many continents including Europe, Americas, and Africa. They are fairly large flies, nearly twice the size of the housefly, with a metallic blue abdomen and long orange setae on the gena.
Forensic entomological decomposition is how insects decompose and what that means for timing and information in criminal investigations. Medicolegal entomology is a branch of forensic entomology that applies the study of insects to criminal investigations, and is commonly used in death investigations for estimating the post-mortem interval (PMI). One method of obtaining this estimate uses the time and pattern of arthropod colonization. This method will provide an estimation of the period of insect activity, which may or may not correlate exactly with the time of death. While insect successional data may not provide as accurate an estimate during the early stages of decomposition as developmental data, it is applicable for later decompositional stages and can be accurate for periods up to a few years.
Lucilia illustris is a member of the fly family Calliphoridae, commonly known as a blow fly. Along with several other species, L. illustris is commonly referred to as a green bottle fly. Lucilia illustris is typically 6–9 mm in length and has a metallic blue-green thorax. The larvae develop in three instars, each with unique developmental properties. The adult fly typically will feed on flowers, but the females need some sort of carrion protein in order to breed and lay eggs.
Phormia regina, the black blow fly, belongs to the blow fly family Calliphoridae and was first described by Johann Wilhelm Meigen.
Nicrophorus tomentosus is a species of burying beetle that was described by Friedrich Weber in 1801. The beetle belongs to the family Silphidae which are carrion beetles. The beetles have sensitive antennae that contain olfactory organs. Thus, the beetle can locate dead animals (carcass), and then as the name suggests, can bury them. However, unlike other burying beetles, N. tomentosus does not completely bury these brood carcasses. They instead dig a shallow hole under the carcass and cover it with leaf litter. Recognition of these beetles can be distinguished by its black color with orange markings on the wing covers (elytra).
Nicrophorus pustulatus, also known as the pustulated carrion beetle or blistered burying beetle, is a species of burying beetle that was described by Johann Karl Wilhelm Illiger in 1807. This species is native to North America. N. pustulatus exhibits unique habitat utilization and breeding behaviour relative to other members of the genus. This species may be the only described example of a true parasitoid targeting a vertebrate host.
Nicrophorus quadripunctatus is a species of burying beetle that predominates in East Asia. First described by German entomologist Ernst Kraatz in 1877, this beetle has since been the subject of much scientific inquiry—particularly concerning its parental care. Like other burying beetles, N. quadripunctatus inhabit small, vertebrate animal carcasses. This environment provides the beetles with the requisite nutrients for themselves and their offspring. To limit resource theft and predation, the carcass is buried underground. For additional protection, a single, dominant male-female pair guards the carcass cooperatively.
Nicrophorus orbicollis is a nearctic burying beetle first described by Thomas Say in 1825. It is a member of the genus Nicrophorus or sexton beetles, comprising the most common beetles in the family Silphidae. This species is a decomposer feeding on carcasses of small dead animals. N. orbicollis can be used for scientific research both medically and forensically.
The American carrion beetle is a North American beetle of the family Silphidae. It lays its eggs in, and its larvae consume, raw flesh and fungi. The larvae and adults also consume fly larvae and the larvae of other carrion beetles that compete for the same food sources as its larvae.
Sarcophaga bullata, or the grey flesh fly, is a species of fly belonging to the family Sarcophagidae. It varies in size from small to large, 8 to 17 millimeters in length and is very similar in appearance and behavior to a closely related species, Sarcophaga haemorrhoidalis. S. bullata is a common scavenger species in the Eastern United States, but is found throughout the Nearctic region. Identification down to the species level in the family Sarcophagidae is notably difficult and relies primarily on the male genitalia. Though limited information is available regarding S. bullata, it has gained increasing recognition in the field of forensic entomology as a forensically relevant fly species, as it may be among the first species to colonize human remains. In these instances, recovered maggots may be analyzed for post-mortem interval (PMI) estimations, which may be used as evidence in courts of law. Current studies regarding S. bullata have revealed a maternal effect operating in these flies that prevents pupal diapause under certain environmental conditions, which is an important factor to be considered during forensic analyses.
Cynomya cadaverina, also known as the shiny blue bottle fly, is a member of the family Calliphoridae, which includes blow flies as well as bottle flies. In recent years, this family has become a forensically important facet in many medicocriminal investigations in the growing field of forensic entomology. C. cadaverina is specifically important in determining a post-mortem interval, as well as other important factors.
Lucilia coeruleiviridis, formerly Phaenecia coeruleiviridis, is commonly known as a green bottle fly, because of its metallic blue-green thorax and abdomen. L. coeruleiviridis was first discovered by French entomologist Pierre-Justin-Marie Macquart in 1855. It belongs to the family Calliphoridae and is one of many forensically important Diptera, as it is often found on decaying substances. L. coeruleiviridis is one of the most ubiquitous blow fly species in the southeastern United States, particularly in the spring and fall months.
Oiceoptoma noveboracense is a member of the family Silphidae, or carrion beetles, which feed on decaying organic matter such as dead animals. Its common name is the margined carrion beetle, from the orange-red margins on the pronotum, which are helpful when identifying this species. The larva is typically light brown to red and also has vertical ridges on its thorax like the adult. This diurnal beetle can be found mainly in the spring into the fall, and it has a strong preference towards a deciduous forest habitat. The primary forensic importance of this beetle is its ability to use the succession of insect fauna to provide confirmation of postmortem intervals.
Calliphora loewi is part of the family Calliphoridae, bottle flies and blowflies, and in the genus Calliphora, blue bottle flies. The genus can be deceiving since C. loewi is not blue. Though this species is rare, it can play an important part in forensic entomology, spreading disease, and decomposing carrion. The life cycle of C. loewi is similar to the life cycle of the genus Calliphora. Since this species is rare there has not been very much research done with this species.
Carrion insects are insects associated with decomposing remains. The processes of decomposition begin within a few minutes of death. Decomposing remains offer a temporary, changing site of concentrated resources which are exploited by a wide range of organisms, of which arthropods are often the first to arrive and the predominant exploitive group. However, not all arthropods found on or near decomposing remains will have an active role in the decay process.