Silphidae

Silphidae Temporal range:
Nicrophorus vespillo
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Coleoptera
Suborder:	Polyphaga
Infraorder:	Staphyliniformia
Superfamily:	Staphylinoidea
Family:	Silphidae Latreille,1806
Subfamilies
NicrophorinaeKirby,1837 SilphinaeLatreille,1806

Silphidaeis a family ofbeetlesthat are known commonly aslarge carrion beetles,carrion beetlesorburying beetles.There are twosubfamilies:SilphinaeandNicrophorinae.Members of Nicrophorinae are sometimes known asburying beetlesorsexton 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 decayingorganic mattersuch as dead animals. The subfamilies differ in which usesparental careand which types of carcasses they prefer. Silphidae are considered to be of importance toforensic entomologistsbecause when they are found on a decaying body they are used to help estimate apost-mortem interval.

Taxonomy, evolution, and etymology

The family 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 familyAgyrtidaewere included. This family has two subfamilies,SilphinaeandNicrophorinae.The antenna is made up of 15 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 largecarrion.Nicrophorinae breed on small animalcarrionand will bury themselves and their food to rear their offspring in a bi-parental manner.There are approximately 183 species in this family, which are found worldwide although they are commoner in temperate regions.Nicrophorus americanus,known as the American burying beetle, is anendangered species.

The oldest fossils of silphids are known from the Middle Jurassic (~ 163 million years ago)Daohugou Bedin Northern China.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 onvertebratecarcasses, whereas flightless species will feed on soilinvertebrates.They also found that egg production increased with flight loss because of a more limited food supply.

Ridged Carrion Beetle (Oiceoptoma inaequale)

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 wordsilvameaning "forests" or "of the woods".

Diversity and distribution

Silphidae areubiquitousand 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 that ants, flies and other carrion feeders outcompete them in these regions.They vary in size from 7 to 45 mm.

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.A species found in Great Britain isOiceoptoma thoracicum.

One species of Nicrophorus beetle within the family Silphidae,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.

Development

Silphidae undergoholometabolousdevelopment. The development in the subfamily Silphinae proceeds at a slower rate than in Nicrophorinae. The Silphinaelife cycletakes approximately twenty six to fifty eight days to go from an egg to adult. The breakdown of this process is essential toforensic entomologists.The cycle takes two to seven days after the egg is laid to hatch. Thelarvaewill develop through threeinstarson thecarrionlasting for ten to thirty days. After that time period is up the third instar larvae will venture away from thedetritustopupate.Pupation takes fourteen to twenty one days and is the major part ofmetamorphosiswhere a grandiose change occurs. During this stage the wings become fully developed and sexual maturity is reached, sometimes called theimagoor adult stage where the cycle is then repeated. The Nicrophorinae cycle is generally quicker.Ovipositionis done near thecarcassand takes twelve to forty eight hours for the eggs to hatch intolarvae.The amount of food andparental careexhibited 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.

Reproduction

Male (left) and femaleNecrophila americana

Nicrophorinae are well known for the habit of locating acarcassand 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 largecarrionmales 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 thecarrionand if any eggs have been laid they are killed so the new female can lay her own.

Behavior and ecology

Food

Nicrophorus vespilloidescolonizing a dead rodent.

Silphid adults feed in a saprophagous manner: they colonize thecarrionduring 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 subfamily Silphinae is themaggotmass present on thedetritus.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 thecarcass.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 apost-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 thedetritusfor 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 majorcompetitorof silphids fordetritus.If a carcass is infested with maggots, many of the Nicrophorinae will abandon the carcass while members of Silphinae will feed on the maggots.

Defense

Beetles have many different weapons available to protect them againstpredatorattacks. The members of Silphidae have many different modifications that allow them to thrive in differentecological nichesincluding colour warnings (fromaposematismtoBatesian 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 nicrophorines have bright orange coloring on theirelytra,which may serve as a warning to other predators.Some species secrete a chemical from a rectal gland that consists ofaliphatic acidsandterpene alcohols.The secretion has a strong, foul odor and may betopicallyirritating tocockroachesandflies.The speciesNecrodes surinamensisejects this secretion as a spray and can rotate the end of its abdomen to spray in all directions.

Locomotion and navigation

Walking is the primary form of locomotion for Silphidae beetles. They are able to travel great distances to findcarcassesto breed and feed on. Beetles also have two sets of wings, theelytraand 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 sulfideand somecyclic compoundsare released. Silphidae use their sense of smell to locate carcasses from a long distance bychemoreceptorson their antennae, which are adapted to detect these chemicals.At a short distance, the end organs of the palpi detect the odors.Silphid beetles are usually more active at night,nocturnal,which may help reduce competition.

Competition

Competitionfrom other organisms for thecarrionputs the Silphids at both an advantage and a disadvantage. The advantage is that fly competitors lay eggs that result inmaggotsand supply food for Silphids. The disadvantage for the Nicrophorinae is that if the carcass is already “blown”, referring toShakespeareantime as being infected with fly maggots, they will not colonize. Nicrophorinae have adapted to these situations and will bury thecarcassto remove it from other competitors.With this technique, a steady food source is available for the larvae andprocreationchances increase.

Silphidae compete forbroodingareas. If an invader male overpowers the original male, it will mate with the original female and create a newbrood.If an invader female overpowers the original female, it will also create a newbroodwith the primary male.

Relationships

With humans

Silphids are usually not considered anuisanceto humans. They help the environment by laying their eggs oncarcassesand the larvae break down thedetritus,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 opacain Europe feed on beets.Necrophila americanafeed on pumpkin, spinach, and sugar beet.

With other organisms

Members from the family Silphidae are known to have mutualistic relationships with other organisms. Nicrophorinae have a mutual relationship with phoreticmites.Mites from the genusPoecilochirusproduce deutonymphs that crawl on Nicrophorinae and are transported tocarrion.Once they arrive at thecarrion,deutonymphs leave the adult Nicrophorinae and proceed to feed on nearby fly eggs and immaturelarvae.Mites help Nicrophorinae reduce the number of competitors oncarrion.With less competition, both species are able to reproduce successfully underground.

Silphidae are known for being hosts to juvenilenematodes.Nicrophorus vespilloidesare closely associated with thenematodeparasite. The parasites can be easily transmitted to other hosts duringcopulation.

Forensic research

Silphidae are one of several families offorensicimportance in the orderColeoptera.They are a very important tool in determining apost-mortem intervalby 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 utilizingarthropodsasevidenceto aid in solving crimes.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 heavilysclerotizedareas of the larvae instead of measuring just the length, which is subject to change with each larva, particularly inO. inaequaleandN. 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.

Silphidae are being studied to find more exact estimations ofpost-mortem intervalsand possible manners of death.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 thecoleopteransto come in contact withcarrion.Silphidaelarvaeare opportunisticpredatorsthat will feed ondipteraneggs, larvae, and on the carcass itself.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, someParasitidaemites (for example,Poecilochirusspecies) are used due to their phoront-host specificity. If a corpse is invaded byPoecilochirusspecimens and no Silphidae were sampled by forensic entomologists, it is reasonable to suspect that some Silphidae carryingPoecilochirusphoretic instars arrived previously to the corpse and abandoned it some time later, leavingPoecilochirusmites in the process.

External links

• Horn, GH (1880) Synopsis of the Silphidae of the United States with reference to the genera of other countries.