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Taxonomy
Silphidae
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The Silphidae are among the largest and most conspicuous of the staphylinoid beetles. Most species are carrion-associated and will breed at carrion on which the larvae will feed. Adults of some (most?) species will opportunistically prey on fly larvae, and various species have been found at both dung and certain fungi.
There are two distinct lineages or clades of silphids currently ranked as subfamilies. The Silphinae typically breed at large carcasses and show little to no parental care whereas the Nicrophorinae, in particular the genus Nicrophorus, show the opposite pattern. They breed at small carcasses (<300g, usually <50g) which a pair of parents will bury into a subterranean crypt in which to rear their brood. Members of the genus Nicrophorus are unusual among the Coleoptera in showing biparental care of their offspring. Some species have been found to breed communally on carcasses too large to bury.
There is a relatively extensive literature on silphid biology, although primarily focused on the more behaviorally complex species of the Nicrophorinae, much of which has been reviewed by Anderson and Peck (1985), Ratcliffe (1996), Eggert and Müller (1997) and Scott (1998). Heymons published a series of classic works describing the biology of various European silphine species (Heymons et al. 1926, 1927, 1928, 1929, 1930a, 1930b; Heymons & Lengerken 1931, 1932a, 1933b, 1934). The life history of Necrodes surinamensis was described by Ratcliffe (1972) but few other silphine species have been studied in detail. See Sikes (in press) for more detailed information on silphid biology, morphology, and phylogeny.
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The Silphidae, as currently defined with only two subfamilies (Lawrence & Newton 1982), has been considered "undoubtedly monophyletic" (Hansen 1997). However, we cannot consider the monophyly of the Silphidae to be adequately tested at this point because we do not yet know what group is the sister lineage to the silphids. Hatch (1927) classified the silphids as a subfamily of the Staphylinidae near the Omaliinae but his classification did not gain acceptance. More recent works place silphids very close to, or tentatively inside the Staphylinidae (e.g. Lawrence & Netwon 1982; Lawrence 1982, Hansen 1997, Caterino et al. 2005) but many hypotheses remain unsatisfactorily tested. The consensus literature treats the group as a distinct family in a similar manner to the earlier classification of the tiger beetles as a family (Cicindelidae) that are now placed as a subgroup (Cicindelitae) within the ground beetles (Carabidae).
All but the first of Hansen's proposed silphid synapomorphies (see Characteristics) are convergent with one or more of the staphyliniform ingroup taxa in his study; leaving only one unique character state supporting the monophyly of the Silphidae (subapical bulge on each elytron).
Beutel and Molenda (1997) analyzed larval characters and found 3 of the 33 characters in their analysis to be derived (apomorphic) for the Silphidae, but none were uniquely so. There are a number of potential characters that have not been fully investigated which could prove to be synapomorphies of the Silphidae such as the pair of eggbursters on the hypopharynx of silphid first instars and the position in which adults hold their elytra during flight.
Nicrophorus kieticus about to fly showing position that the elytra are held during flight. Image copyright © 2005 Derek S. Sikes.
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Source | http://tolweb.org/Silphidae/9620 |
Hansen (1997) listed 13 possible synapomorphies of the Silphidae:
- Subapical bulge on each elytron
- Relatively large clypeus
- Mandibles without a mola
- Antennal insertions on dorsal face of head
- Cupuliform segment 8 of antenna
- Antenna with well defined, densely pubescent, 3 segmented club
- Abdominal segment 9 and 10 everted
- Abdominal terga 1-3 weakly sclerotized
- Abdominal sternum 2 well demarcated and visible
- Noncarinate basal ventrite
- Inflexed portion of abdominal sterna demarcated but not articulated to ventral portion
- Gonocoxites relatively short and flat
- Larval galea present as a small (fixed) appendage on lacinia
Silphids are dorso-ventrally flattened beetles and are among the largest-bodied of the staphylinoids, typically ranging in length from 12-20 mm. Their antennae are eleven segmented, however, species in the subfamily Nicrophorinae have a greatly reduced pedicel (antennomere 2) that is fused to the scape (antennomere 1) making them appear to have a 10 segmented antenna. Species in the subfamily Silphinae lack a frontoclypeal (epistomal) suture. Species in the subfamily Nicrophorinae bear a pair of stridulatory files on the 5th abdominal tergite (just under the apex of the elytra). The scutellum of silphids is very large, sometimes as wide as the head:
Dorsal view of the head and thorax of Diamesus showing the large scutellum. Image copyright © 2005 Derek S. Sikes.
The larvae differ between the subfamilies with silphine larvae bearing a cluster of 6 stemmata (ocelli) on each side of the head and nicrophorine larvae bearing only a single stemma on each side. In addition, the larvae of the Silphinae are strongly and widely sclerotized whereas the larvae of the Nicrophorinae (particularly Nicrophorus) are weakly and sparsely sclerotized:
Larvae of A) Nicrophorus sp. and B) Silphinae gen. sp.. Image copyright © 2005 Derek S. Sikes.
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Source | http://tolweb.org/Silphidae/9620 |
Silphidae (silphids) preys on:
Mammalia
Based on studies in:
Costa Rica (Carrion substrate)
This list may not be complete but is based on published studies.
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Well supported basal split dividing the family into two subfamilies.
Dobler and Müller (2000) used sequences of the genes COI and COII to infer the phylogenetic relationships for 11 genera of the Silphinae and 2 of the Nicrophorinae. Their results strongly supported the monophyly of two main clades in the Silphidae that correspond to the subfamilies Silphinae and Nicrophorinae and most included genera with the exception of Silpha (which was recovered as paraphyletic with respect to Aclypea).
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Rights holder/Author | Derek S. Sikes, Stephen T. Trumbo, Stewart B. Peck, Tree of Life web project |
Source | http://tolweb.org/Silphidae/9620 |
Barcode of Life Data Systems (BOLD) Stats
Specimen Records:1024
Specimens with Sequences:834
Specimens with Barcodes:612
Species:109
Species With Barcodes:99
Public Records:436
Public Species:78
Public BINs:70
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. Nicrophorines are sometimes known as sexton beetles. The number of species is relatively small and around two hundred. They are more diverse in the temperate region although a few tropical endemics are known. Both families feed on decaying organic matter such as dead animals. The families 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 (PMI).
Contents
Taxonomy, evolution and etymology[edit]
The family Silphidae belongs to the order Coleoptera. They are commonly referred to as carrion beetles or burying beetles and are usually associated with carrion, fungi, and dung. In the past, members of the family Agyrtidae were included. This family has two subfamilies, Silphinae and Nicrophorinae. The antenna is made up of 11 segments and is capitate (ending in an abruptly capped club) in the Nicrophorinae and has a more gradual club shape in the Silphinae. The subfamilies also differ in behavior. Members of the subfamily Silphinae show little to no care for their young and breed on large carrion. Nicrophorinae breed on small animal carrion and will bury themselves and their food to rear their offspring in a bi-parental manner.[1] There are approximately 183 species in this family, which are found worldwide although they are commoner in the temperate region. Nicrophorus americanus, known as the American Burying Beetle, is an endangered species.[2]
The oldest beetle fossils are over 265 million years old dating back to the Permian period but the oldest fossil Silphid is that of N. humator dating around 10,500 years and described in 1962 by Pearson.[3] Many Silphidae are flightless although they have wings. This loss is thought to be a result due to the changes in habitat over time. Researchers have found that most flight-capable species in this group feed on vertebrate carcasses, whereas flightless species will feed on soil invertebrates. They also found that egg production increased with flight loss because of a more limited food supply.[4]
The word "silphid" or "sylph", first seen in the sixteenth century in Paracelsus' works, refers to any race of spirits inhabiting the air and is described as mortal, but lacking soul. The word is also related to the Latin word sylva meaning "slender, graceful girl" and the Greek word nymph meaning "light, airy movements".[5]
Diversity and distribution[edit]
Silphidae beetles are ubiquitous and are most abundant in the temperate zone. The diversity is also greater in the temperate zone and they are quite rare in the tropics although there are species endemic in the region. It is thought that ants, flies and other carrion feeders outcompete them in these regions.[6] They vary in size from 7 to 45 mm.[7]
There are about 46 different species of Silphidae in North America which include Heterosilpha ramosa, Necrodes surinamensis, Necrophila americana, Nicrophorus americanus, Nicrophorus carolinus, Nicrophorus investigator, Nicrophorus marginatus, Nicrophorus orbicollis, Nicrophorus tomentosus, Oiceoptoma inaequale, Oiceoptoma noveboracense, Oiceoptoma rugulosum, Thanatophilus lapponicus.[8][9] A species found in the United Kingdom is Oiceoptoma thoracicum.
The Nicrophorinae have a narrower distribution than the Silphinae. Tropical forms include Diamesus of Asia and Australia, Ptomophila in Australia and Nicrophorus mexico of Central America.
Development[edit]
Silphidae undergo holometabolous development. The development in the subfamily Silphinae proceeds at a slower rate than in Nicrophorinae. The Silphinae life cycle takes approximately twenty six to fifty eight days to go from an egg to adult. The breakdown of this process is essential to forensic entomologists. The cycle takes two to seven days after the egg is laid to hatch. The larvae will develop through three instars on the carrion lasting for ten to thirty days. After that time period is up the third instar larvae will venture away from the detritus to pupate. Pupation takes fourteen to twenty one days and is the major part of metamorphosis where a grandiose change occurs. During this stage the wings become fully developed and sexual maturity is reached, sometimes called the imago or adult stage where the cycle is then repeated. The Nicrophorinae cycle is generally quicker. Oviposition is done near the carcass and takes twelve to forty eight hours for the eggs to hatch into larvae. The amount of food and parental care exhibited help determine the length of the larval stage. Pupation in this subfamily lasts six to eight days and is completed in the soil. The adult Nicrophorinae will emerge from the soil and venture to find food and a mate.[8]
Reproduction[edit]
Nicrophorinae are well known for the habit of locating a carcass and burying it by unearthing the soil underneath it. The burying behavior has seemingly evolved to prevent competition from other insects such as fly maggots. It has been observed that the cooperation of the two parent beetles leads to breeding success. More likely than not a breeding pair will work together, but in cases where there is large carrion males try to boost their reproduction by emitting pheromones. In this way, he will father more offspring, but the reproductive success of the primary female steadily declines. Sometimes, where there is a large carcass the likelihood of intense competition from flies leads to communal breeding. There appears to be a truce between females who would normally compete for the males, and in these cases cooperative behavior extends to females caring for each other's offspring. At the height of breeding season pairs of beetles may compete for the carrion. The losing pair will be ejected from the carrion and if any eggs have been laid they are killed so the new female can lay her own.[10]
Behavior and ecology[edit]
Food[edit]
The Silphidae adults feed in a saprophagous manner: they colonize the carrion during all four stages of decomposition, which are fresh, bloated, decay, and dry. The main areas of decomposition for adults are during both the bloated and decaying stages. The Silphidae larvae mainly inhabit during the decaying and dry stages of the carrion. The primary food source for the subfamily Silphinae is the maggot mass present on the detritus. The Nicrophorinae will colonize the body earlier in decomposition in order to avoid competition with maggots. If there is a sufficiently large maggot mass they will not colonize the carcass. The parental care exhibited by this subfamily is that the adult beetles regurgitate food into the mouths of the young larvae until they are mature. Silphinae colonize later in the decaying process and the adults eat the maggot mass, sometimes leaving little maggot evidence left to estimate a post-mortem interval. In the case of the sexton or burying beetles, Nicrophorinae, the adults will bury small animal carcasses and lay their eggs on it. In some species, a slight depression is made on the detritus for maturing larvae that the adult beetles feed and protect. In both subfamilies the larvae are observed to eat the decaying organic material while the adults mainly consume the maggots. Flies are the major competitor of Silphiade for detritus. If a carcass is infested with maggots, many of the Nicrophorinae will abandon the carcass while members of Silphinae will feed on the maggots.[8]
Defense[edit]
Beetles have many different weapons available to protect them against predator attacks. The members of Silphidae have many different modifications that allow them to thrive in different ecological niches including colour warnings (from aposematism to Batesian mimicry), chemical defenses and parental care. Silphid beetles are usually dark in color consisting of gold, black and brown. This dark coloring allows them to blend into their environment. One species of Silphidae uses a physical mean of defense. Oiceoptoma inaequalis holds its elytra over its back when it flies. The back of the elytra are bright blue and when they are exposed it makes the beetle look much larger. After landing, the beetle folds its wings and the blue color vanishes. Many Silphidae have bright orange coloring on their elytra, which may serve as a warning to other predators.[11] Some Silphidae beetles secrete a chemical from a rectal gland that consists of aliphatic acids and terpene alcohols. The secretion has a strong, foul odor and may be topically irritating to Blattodea and Diptera. The species Necrodes surinamensis ejects this secretion as a spray and can rotate the end of its abdomen to spray in all directions.[12]
Locomotion and navigation[edit]
Walking is the primary form of locomotion for Silphidae beetles. They are able to travel great distances to find carcasses to breed and feed on. Beetles also have two sets of wings, the elytra and the hind wings. The hind wings are membranous and are modified for flying or swimming. There are some Silphidae who are able to fly, but others have lost this ability throughout evolution. When an animal dies, hydrogen sulfide and some cyclic compounds are released. Silphidae use their sense of smell to locate carcasses from a long distance by chemoreceptors on their antennae, which are adapted to detect these chemicals.[13] At a short distance, the end organs of the palpi detect the odors.[11] Silphid beetles are usually more active at night, nocturnal, which may help reduce competition.
Competition[edit]
Competition from other organisms for the carrion puts the Silphids at both an advantage and a disadvantage. The advantage is that fly competitors lay eggs that result in maggots and supply food for Silphids. The disadvantage for the Nicrophorinae is that if the carcass is already “blown”, referring to Shakespearean time as being infected with fly maggots, they will not colonize. Nicrophorinae have adapted to these situations and will bury the carcass to remove it from other competitors.[14] With this technique, a steady food source is available for the larvae and procreation chances increase.
Silphidae compete for brooding areas. If an invader male overpowers the original male, it will mate with the original female and create a new brood.[15] If an invader female overpowers the original female, it will also create a new brood with the primary male.
Relationships[edit]
With humans[edit]
Silphids are usually not considered a nuisance to humans. They help the environment by laying their eggs on carcasses and the larvae break down the detritus, which prevents accumulation of deceased organisms.
Carcasses are kept out of sight and foul odors are prevented when Nicrophorinae bury it under the ground. This will also reduce the surface area for flies to lay their eggs and decrease fly population.
Some Silphidae occupy human-inhabited areas and become pests to farmers by using crops as a second source of nutrients. Aclypea opaca in Europe feed on beets. Necrophila americana feed on pumpkin, spinach, and sugar beet.
With other organisms[edit]
Members from the Silphidae family are known to have a mutualistic relationships with other organisms. Nicrophorinae have a mutual relationship with phoretic mites. Mites from the genus Poecilochirus produce deutonymphs that crawl on Nicrophorinae and are transported to carrion. Once they arrive at the carrion, deutonymphs leave the adult Nicrophorinae and proceed to feed on nearby fly eggs and immature larvae. Mites help Nicrophorinae reduce the amount of competitors on carrion. With less competition, both species are able to reproduce successfully underground.[16]
Silphidae are known for being hosts to juvenile nematodes. Nicrophorus vespilloides are closely associated with the nematode parasite. The parasites can be easily transmitted to other hosts during copulation.
Forensic research[edit]
Silphidae are one of several families of forensic importance in the order Coleoptera. They are a very important tool in determining a post-mortem interval by collecting Silphid progeny from the carcass, and determining the developmental rate. Based on the number of instars present and what stage of development they are in, a time of death can be estimated. This is very useful in medicocriminal entomology, the emphasis on utilizing arthropods as evidence to aid in solving crimes.[8] Many of the methods in determining stages of development are subjective. Fortunately, recent studies have found a new way of determining what stage of development Silphid larvae are in by measuring the maximum cranial width and other heavily sclerotized areas of the larvae instead of measuring just the length, which is subject to change with each larva, particularly in O.inaequale and N. surinamensis, which are more robust and have greater variations of length respectively. In terms of future research, Silphidae are being studied to find more exact PMI estimations and possible manners of death.[17] Also, in the future, entomologists will explore the social behavior of the beetles to a greater degree. Members of family Silphidae are typically the first of the coleopterans to come in contact with carrion. Silphidae larvae are opportunistic predators that will feed on dipteran eggs, larvae, and on the carcass itself.[17] This presents a problem in the determination of post-mortem interval (PMI) because Silphidae are known to eradicate other species from carrion. By eliminating the first colonizing species Silphidae can give an incorrect PMI.
References[edit]
- ^ Eggert, A. Muller, J. K. (1997). Bi-parental care and social evolution in burying beetles: Lessons from the larder in Social Behavior in Insects and Arachnids. Cambridge: Cambridge University Press. pp. 1–541.
- ^ Backlund, Douglas C.; Gary M. Marrone, Christopher K. Williams, and Kelley Tilmon (2008). "Population Estimate of the Endangered American Burying Beetle, Nicrophorus americanus Olivier (Coleoptera: Silphidae) in South Dakota.". The Coleopterists Bulletin 62 (4).
- ^ http://collections2.eeb.uconn.edu/nicroweb/PDFs/Sikes_et_al_2002.pdf
- ^ Abe, T. Ikeda, H. Kagaya, T. Kubota, K. (2008). "Evolutionary Relationships Among Food Habitat, Loss of Flight, and Reproductive Traits: Life-History Evolution in the Silphinae(Coleoptera:Silphidae)". Evolution 62 (8): 2065–2079. doi:10.1111/j.1558-5646.2008.00432.x.
- ^ Online Etymology Dictionary. http://www.etymonline.com/index.php?search=nymph
- ^ Ratcliffe B.C. (1996). The carrion beetles (Coleoptera:Silphidae) of Nebraska. Bulletin 13. Lincoln, USA: University of Nebraska State Museum.
- ^ Dekeirsschieter, Jessica; François Verheggen; Georges Lognay; Eric Haubruge (2011). "Large carrion beetles (Coleoptera, Silphidae) in Western Europe: a review". Biotechnol. Agron. Soc. Environ. 15 (3): 435–447.
- ^ a b c d Byrd, Jason H. Castner, James L. title=Forensic Entomology: The Utility of Arthropods in Legal Investigations (2001). Boca Raton: CRC Press LLC. pp. 10, 37, 189–199. Missing or empty
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(help) - ^ Anderson, RS and SB Peck (1985). The insects and arachnids of Canada. Part 13. The Carrion Beetles of Canada and Alaska. Coleoptera: Silphidae and Agyrtidae. Agriculture Canada.
- ^ McGavin, George C. Essential Entomology: An Order-by-Order Introduction. Oxford: Oxford University Press, 2001. pp. 62–66.
- ^ a b Ratcliffe, B. The Carrion Beetles (Coleoptera:Silphidae) of Nebraska. Bulletin of the Nebraska State Museum. Volume 13.
- ^ Roach, B. Eisner, T. Meinwald, J. The Defense Mechanisms of arthropods. 83. alpha-and beta-Necrodol, novel terpens from a carrion beetle (Necrodes surinamensis, Silphidae, Coleoptera)Journal of Organic Chemistry 1990 55 (13), 4047–4051.
- ^ Evans, A. Hogue, J. Introduction to California Beetles. University of California Press 2004. p. 154–156.
- ^ Eggert AK, Reinking M, Muller JK. "Parental Care Improves Offspring Survival and Growth in Burying Beetles." Animal Behavior 55.1 (1998): p. 97–107
- ^ Trumbo ST. "Defending Young Biparentally: Female Risk-Taking with and Without a Male in the Burying Beetle, Nicrophorus pustulatus." Behavioral Ecology and Sociobiology 61.11 (2007): p. 1717–1723
- ^ Grossman J.D., Smith RJ. "Phoretic Mite Discrimination Among Male Burying Beetle (Nicrophorus Investigator) Hosts." Annals of the Entomological Society of America 101.1 (2008): p. 266–271
- ^ a b Watson, E.J. and C.E. Carlton. "Succession of Forensically Significant Carrion Beetle Larvae on Large Carcasses (Coleoptera: Silphidae)." Southeastern Naturalist. 2005. pp. 335–346
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