Silphinae is a subfamily of rove beetles that are also known commonly as large carrion beetles, carrion beetles or burying beetles. There are two tribes: Silphini and Nicrophorini. Members of Nicrophorini 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 tribes feed on decaying organic matter such as dead animals. The tribes differ in which uses parental care and which types of carcasses they prefer. Silphini 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. Traditionally, the subfamily Silphinae was classified as its own family, Silphidae, but multiple lines of evidence show that they evolved from within the family Staphylinidae.
Taxonomy, evolution, and etymology The subfamily Silphinae belongs to the family Staphylinidae in 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 subfamily has two tribes, Silphini and Nicrophorini. 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 large carrion. Nicrophorini breed on small animal carrion and will bury themselves and their food to rear their offspring in a bi-parental manner. 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 an endangered species. The oldest fossils of silphids are known from the Middle Jurassic (~ 163 million years ago) Daohugou Bed in Northern China. Many Silphinae 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.
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 silva meaning "forests" or "of the woods".
Diversity and distribution Silphinae 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 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 Silphinae 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. A species found in Great Britain is Oiceoptoma thoracicum. One species of Nicrophorus, 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 Silphinae undergo holometabolous development. The development in the tribe Silphini proceeds at a slower rate than in Nicrophorini. The Silphini life cycle takes approximately 26 to 58 days to go from an egg to adult. The breakdown of this process is essential to forensic entomologists. Eggs take two to seven days to hatch. The larvae will develop through three instars on the carrion lasting for 10 to 30 days. After that time period is up the third instar larvae will venture away from the detritus to pupate. Pupation takes 14 to 21 days; 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 life cycle of the Nicrophorini is generally quicker. Oviposition is done near the carcass and eggs take 12 to 48 hours 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 Nicrophorine will emerge from the soil and venture to find food and a mate.
Reproduction
Nicrophorini 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.
Behavior and ecology
Food
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