Silphidae

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 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. 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. 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. 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. 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. 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'. 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. They vary in size from 7 to 45 mm. 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. A species found in Great Britain 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. 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.