 | This article needs to beupdated. The reason given is:Silphidae is now considered a subfamily ofStaphylinidae in a number of recently published works, e.g. in[1],[2] and[3], as well as inBugGuide. Subfamilies Nicrophorinae and Silphinae are now tribes Nicrophorini and Silphini. Please help update this article to reflect recent events or newly available information.(January 2025) |
| Silphidae | |
|---|---|
 | |
| Nicrophorus vespillo | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Coleoptera |
| Suborder: | Polyphaga |
| Infraorder: | Staphyliniformia |
| Superfamily: | Staphylinoidea |
| Family: | Silphidae Latreille, 1806[1] |
| Tribes | |
NicrophoriniKirby, 1837 | |
Silphidae is a subfamily ofbeetles that are known commonly aslarge carrion beetles,carrion beetles orburying beetles. There are twotribes:Silphini andNicrophorini. Members of Nicrophorini are sometimes known asburying beetles orsexton beetles. The number of species is relatively small, at around two hundred. They are more diverse in thetemperate region although a few tropical endemics are known. Both tribes feed on decayingorganic matter such as dead animals. The tribes differ in which usesparental care and which types of carcasses they prefer. Silphidae are considered to be of importance toforensic entomologists because when they are found on a decaying body they are used to help estimate apost-mortem interval.
The subfamily Silphidae belongs to the orderColeoptera. They are commonly referred to as carrion beetles or burying beetles and are usually associated withcarrion,fungi, anddung. In the past, members of the familyAgyrtidae were included. This subfamily has two tribes,Silphini andNicrophorini. The antenna is made up of 15 segments and is capitate (ending in an abruptly capped club) in the Nicrophorini and has a more gradual club shape in the Silphini. The tribes also differ in behavior. Members of the tribe Silphini show little to no care for their young and breed on largecarrion. Nicrophorini breed on small animalcarrion and will bury themselves and their food to rear their offspring in a bi-parental manner.[2] There are approximately 183 species in this subfamily, which are found worldwide although they are more common in temperate regions.Nicrophorus americanus, known as the American burying beetle, is anendangered species.[3]
The oldest fossils of silphids are known from the Middle Jurassic (~ 163 million years ago)Daohugou Bed in Northern China.[4][5] 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 onvertebrate carcasses, whereas flightless species will feed on soilinvertebrates. They also found that egg production increased with flight loss because of a more limited food supply.[6]
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The word "silphid" or "sylph", first seen in the sixteenth century inParacelsus' 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 wordsilva meaning "forests" or "of the woods".[7]
Silphidae areubiquitous 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 to the region. It is thought thatants,flies and other carrion feeders outcompete them in these regions.[8] They vary in size from 7 to 45 mm.[9]
There are about 46 different species of Silphidae in North America which includeHeterosilpha 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.[10][11] A species found in Great Britain isOiceoptoma thoracicum.
One species ofNicrophorus,Nicrophorus nepalensis, can be found primarily in the mountains of eastern Asia as well as along the Malay Archipelago.Nicrophorus nepalensis are found in the Indian subcontinent as well in the countries of India and Pakistan.
Silphidae undergoholometabolous development. The development in the subfamily Silphini proceeds at a slower rate than in Nicrophorini. The Silphinilife cycle takes approximately 26 to 58 days to go from an egg to adult.[citation needed] The breakdown of this process is essential toforensic entomologists. Eggs take two to seven days to hatch. Thelarvae will develop through threeinstars on thecarrion lasting for 10 to 30 days. After that time period is up the third instar larvae will venture away from thedetritus topupate. Pupation takes 14 to 21 days; during this stage the wings become fully developed and sexual maturity is reached, sometimes called theimago or adult stage where the cycle is then repeated. The life cycle of the Nicrophorini is generally quicker.Oviposition is done near thecarcass and eggs take 12 to 48 hours to hatch intolarvae. The amount of food andparental 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 Nicrophorine will emerge from the soil and venture to find food and a mate.[10]
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Nicrophorini are well known for the habit of locating acarcass and burying it by unearthing the soil underneath it. The burying behavior has seemingly evolved to prevent competition from other insects such as flymaggots. 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 largecarrion males try to boost their reproduction by emittingpheromones. 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 tocommunal 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 thecarrion. The losing pair will be ejected from thecarrion and if any eggs have been laid they are killed so the new female can lay her own.[12]
Silphid adults feed in a saprophagous manner: they colonize thecarrion during all four stages ofdecomposition, which are fresh, bloated, decay, and dry. The main areas of decomposition for adults are during both the bloated and decaying stages. Silphid larvae mainly inhabit during the decaying and dry stages of thecarrion. The primary food source for the tribe Silphini is themaggot mass present on thedetritus. Nicrophorini 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 thecarcass. The parental care exhibited by this tribe is that the adult beetles regurgitate food into the mouths of the young larvae until they are mature. Silphini colonize later in the decaying process and the adults eat the maggot mass, sometimes leaving little maggot evidence left to estimate apost-mortem interval. In the case of the sexton or burying beetles, Nicrophorini, the adults will bury small animal carcasses and lay their eggs on it. In some species, a slight depression is made on thedetritus 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 majorcompetitor of silphids fordetritus. If a carcass is infested withmaggots, many of the Nicrophorini will abandon the carcass while members of Silphini will feed on the maggots.[10]
Beetles have many different weapons available to protect them againstpredator attacks. The members of Silphidae have many different modifications that allow them to thrive in differentecological niches including colour warnings (fromaposematism toBatesian mimicry), chemical defenses andparental care. Silphines are usually dark in color consisting of gold, black and brown. This dark coloring allows them to blend into their environment. Many nicrophorini have bright orange coloring on theirelytra, which may serve as a warning to other predators.[13] Some species secrete a chemical from a rectal gland that consists ofaliphatic acids andterpene alcohols. The secretion has a strong, foul odor and may betopically irritating tocockroaches andflies. The speciesNecrodes surinamensis ejects this secretion as a spray and can rotate the end of its abdomen to spray in all directions.[14]
Walking is the primary form of locomotion for Silphidae. They are able to travel great distances to findcarcasses to breed and feed on. Beetles also have two sets of wings, theelytra 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 throughoutevolution. When an animal dies,hydrogen sulfide and somecyclic compounds are released. Silphidae use their sense of smell to locate carcasses from a long distance bychemoreceptors on their antennae, which are adapted to detect these chemicals.[15] At a short distance, the end organs of the palpi detect the odors.[13] Silphid beetles are usually more active at night,nocturnal, which may help reduce competition.
Competition from other organisms for thecarrion puts the silphids at both an advantage and a disadvantage. The advantage is that fly competitors lay eggs that result inmaggots and supply food for silphids. The disadvantage for the Nicrophorini is that if the carcass is already “blown”, referring toShakespearean time as being infected with fly maggots, they will not colonize. Nicrophorini have adapted to these situations and will bury thecarcass to remove it from other competitors.[16] With this technique, a steady food source is available for the larvae andprocreation chances increase.
Silphidae compete forbrooding areas. If an invader male overpowers the original male, it will mate with the original female and create a newbrood.[17] If an invader female overpowers the original female, it will also create a newbrood with the primary male.
Silphids are usually not considered anuisance to humans. They help the environment by laying their eggs oncarcasses and the larvae break down thedetritus, which prevents accumulation of deceased organisms.
Carcasses are kept out of sight and foul odors are prevented when Nicrophorini bury it under the ground. This will also reduce the surface area for flies to lay their eggs and decrease fly population.
Some Silphidae species inhabit human-occupied areas and become pests to farmers by using crops as an additional source of nutrients. In Europe,Aclypea opaca feeds on beets, whileNecrophila americana feeds on pumpkins, spinach, and sugar beets.
Members from the subfamily Silphidae are known to have mutualistic relationships with other organisms. Nicrophorini have a mutual relationship with phoreticmites. Mites from the genusPoecilochirus producedeutonymphs that crawl on Nicrophorini and are transported tocarrion. Once they arrive at thecarrion, deutonymphs leave the adult Nicrophorini and proceed to feed on nearby fly eggs and immaturelarvae. Mites help Nicrophorini reduce the number of competitors oncarrion. With less competition, both species are able to reproduce successfully underground.[18]
Silphidae are known for being hosts to juvenilenematodes.Nicrophorus vespilloides are closely associated with thenematode parasite. The parasites can be easily transmitted to other hosts duringcopulation.
Silphidae are one of several families offorensic importance in the orderColeoptera. They are a very important tool in determining apost-mortem interval (PMI) by collecting Silphid progeny from thecarcass, and determining the developmental rate. Based on the number of instars and the larval development stage, a time of death can be estimated. This is very useful inmedicocriminal entomology, the emphasis on utilizingarthropods asevidence to aid in solving crimes.[10] Many of the methods in determining stages of development are subjective. However, recent studies have found a more precise way of determining the stage of development of Silphid larvae by measuring the maximum cranial width and other heavilysclerotized areas of the larvae instead of measuring just the length, which is subject to change with each larva, particularly inO. inaequale andN. surinamensis, which are more robust and have greater variations of length. The most accurate instar identification is possible by using distinct morphological features that are instar specific and cannot be affected by the size of the specimen. Although this is possible only for few species with described larvae of all instars, such asThanatophilus rugosus.[19]
Silphidae are being studied to find more exact estimations ofpost-mortem intervals and possible manners of death.[20] Also, in the future, entomologists will explore the social behavior of the beetles to a greater degree. Members of Silphidae are typically the first of thecoleopterans to come in contact withcarrion. Silphidaelarvae are opportunisticpredators that will feed ondipteran eggs, larvae, and on the carcass itself.[20] This presents a problem in the determination of post-mortem interval because Silphidae are known to eradicate other species from carrion. By eliminating the first colonizing species Silphidae can give an incorrect post-mortem interval.
Unlike most of the insects used as forensic markers, it is possible to assess if Silphidae adults have colonized a corpse and left it later. For this purpose, someParasitidae mites (for example,Poecilochirus species) are used due to their phoront-host specificity. If a corpse is invaded byPoecilochirus specimens and no Silphidae were sampled by forensic entomologists, it is reasonable to suspect that some Silphidae carryingPoecilochirus phoretic instars arrived previously to the corpse and abandoned it some time later, leavingPoecilochirus mites in the process.[21]
