Paederus
Encyclopedia
Paederus is a genus of small beetles of the family Staphylinidae ("rove beetles"). Due to toxins in the hemolymph
of many species within this genus, it has given its name to paederus dermatitis
, a characteristic skin irritation that occurs if one of the insects is crushed against skin. A scholarly paper in 2002 suggested that a Paederus species could have been responsible for some of the ten Plagues of Egypt
described in the Bible
's Book of Exodus.
Paederus species are widely distributed around the world. They are much more brightly colored than other rove beetles, with metallic blue- or green-colored elytra and bright orange or red on the pronotum and the basal segments of the abdomen. These bright colors may be an example of aposematism
, a warning signal to potential predators.
Although most adult rove beetles avoid daylight, Paederus species are active during the day and attracted to bright lights after nightfall.
Paederus eggs are laid singly, in moist habitats. Larvae go through two instars before pupation. Both larvae and adults are predatory on other insects. Because of their preference for moist soil, large numbers of Paederus beetles may be attracted to irrigated farmland, where they provide some benefit by eating herbivorous insects but can cause problems for people working in fields or grassy areas.
, a vesicant toxin in the hemolymph of many but not all females in the genus Paederus. The toxin is manufactured, not by the beetles themselves, but by endosymbiont
bacteria, probably some species of Pseudomonas
.
Once pederin is on the skin from the initial beetle contact, it may also be spread elsewhere on the skin. "Kissing" or "mirror-image" lesions where two skin areas come in contact (for example, the elbow flexure) are often seen. Washing the hands and skin with soap and water is strongly recommended, if contact with a rove beetle has occurred.
Initial skin contact with pederin shows no immediate result. Within 12–36 hours, however, a reddish rash (erythema
) appears, which develops into blisters. Irritation, including crusting and scaling, may last from two to three weeks.
suggests that events like those described as the first two of the ten plagues of Egypt (anoxic die-off in the Nile, followed by many dead frogs) would have created ideal breeding conditions for P. alfierii. The authors suggest that the plague of "boils" could be the skin irritation, typically delayed by a day or more, resulting from contact with Paederus during the third or fourth plagues (lice or flies). They also note that Paederus infestations are often localized, so it would be quite possible for them to have invaded Pharaoh's palace but not the homes of the Jews.
Many modern occurrences of localized but intense Paederus impact are documented in research papers with titles like "An outbreak of paederus dermatitis in a suburban hospital in Sri Lanka", "An outbreak of 268 cases of Paederus dermatitis in a toy-building factory in central China", "Outbreak of dermatitis linearis caused by Paederus ilsae and Paederus iliensis (Coleoptera: Staphylinidae) at a military base in Iraq", and "Evacuation of an Aboriginal community in response to an outbreak of blistering dermatitis induced by a beetle (Paederus australis)".
Hemolymph
Hemolymph, or haemolymph, is a fluid in the circulatory system of some arthropods and is analogous to the fluids and cells making up both blood and interstitial fluid in vertebrates such as birds and mammals...
of many species within this genus, it has given its name to paederus dermatitis
Paederus dermatitis
Paederus dermatitis is skin irritation resulting from contact with the hemolymph of certain rove beetles, a group that includes the genus Paederus...
, a characteristic skin irritation that occurs if one of the insects is crushed against skin. A scholarly paper in 2002 suggested that a Paederus species could have been responsible for some of the ten Plagues of Egypt
Plagues of Egypt
The Plagues of Egypt , also called the Ten Plagues or the Biblical Plagues, were ten calamities that, according to the biblical Book of Exodus, Israel's God, Yahweh, inflicted upon Egypt to persuade Pharaoh to release the ill-treated Israelites from slavery. Pharaoh capitulated after the tenth...
described in the Bible
Bible
The Bible refers to any one of the collections of the primary religious texts of Judaism and Christianity. There is no common version of the Bible, as the individual books , their contents and their order vary among denominations...
's Book of Exodus.
Description
Like other beetles (Coleoptera), rove beetles have a hardened forewing (elytrum, plural elytra) that covers the wings used to fly. At one time, the rove beetle group was known as "Brachyptera" (short wings), because their wings are short and hidden under the short elytra.Paederus species are widely distributed around the world. They are much more brightly colored than other rove beetles, with metallic blue- or green-colored elytra and bright orange or red on the pronotum and the basal segments of the abdomen. These bright colors may be an example of aposematism
Aposematism
Aposematism , perhaps most commonly known in the context of warning colouration, describes a family of antipredator adaptations where a warning signal is associated with the unprofitability of a prey item to potential predators...
, a warning signal to potential predators.
Although most adult rove beetles avoid daylight, Paederus species are active during the day and attracted to bright lights after nightfall.
Paederus eggs are laid singly, in moist habitats. Larvae go through two instars before pupation. Both larvae and adults are predatory on other insects. Because of their preference for moist soil, large numbers of Paederus beetles may be attracted to irrigated farmland, where they provide some benefit by eating herbivorous insects but can cause problems for people working in fields or grassy areas.
Pederin
According to Medical and Veterinary Entomology (2009) "At least 20 of the more than 600 species of Paederus beetles have been associated with Paederus dermatitis", even though Paederus beetles do not bite or sting. This skin irritation results from contact with pederinPederin
Pederin is a vesicant toxic amide with two tetrahydropyran rings, found in the haemolymph of the Paederus genus of beetles, including the Nairobi fly, belonging to the Staphylinidae family. It was first characterized by processing 25 million field-collected P. fuscipes. It makes up approximately...
, a vesicant toxin in the hemolymph of many but not all females in the genus Paederus. The toxin is manufactured, not by the beetles themselves, but by endosymbiont
Endosymbiont
An endosymbiont is any organism that lives within the body or cells of another organism, i.e. forming an endosymbiosis...
bacteria, probably some species of Pseudomonas
Pseudomonas
Pseudomonas is a genus of gammaproteobacteria, belonging to the family Pseudomonadaceae containing 191 validly described species.Recently, 16S rRNA sequence analysis has redefined the taxonomy of many bacterial species. As a result, the genus Pseudomonas includes strains formerly classified in the...
.
Impact on human beings
Paederus dermatitis is caused when a pederin-containing beetle is crushed, even partially, against the skin. This skin irritation is also called "dermatitis linearis" or "linear dermatitis" because one can inadvertently drag a beetle across the skin in a more-or-less straight line when trying to brush it away. The resulting inflammation will also be linear. Because Paederus species are widely dispersed around the world, this syndrome has many different local nicknames including "whiplash dermatitis", "spider lick", and "Nairobi fly dermatitis". Conjunctivitis from getting pederin in the eye is called "Nairobi eye".Once pederin is on the skin from the initial beetle contact, it may also be spread elsewhere on the skin. "Kissing" or "mirror-image" lesions where two skin areas come in contact (for example, the elbow flexure) are often seen. Washing the hands and skin with soap and water is strongly recommended, if contact with a rove beetle has occurred.
Initial skin contact with pederin shows no immediate result. Within 12–36 hours, however, a reddish rash (erythema
Erythema
Erythema is redness of the skin, caused by hyperemia of the capillaries in the lower layers of the skin. It occurs with any skin injury, infection, or inflammation...
) appears, which develops into blisters. Irritation, including crusting and scaling, may last from two to three weeks.
Mass infestations with Paederus beetles
An article in The LancetThe Lancet
The Lancet is a weekly peer-reviewed general medical journal. It is one of the world's best known, oldest, and most respected general medical journals...
suggests that events like those described as the first two of the ten plagues of Egypt (anoxic die-off in the Nile, followed by many dead frogs) would have created ideal breeding conditions for P. alfierii. The authors suggest that the plague of "boils" could be the skin irritation, typically delayed by a day or more, resulting from contact with Paederus during the third or fourth plagues (lice or flies). They also note that Paederus infestations are often localized, so it would be quite possible for them to have invaded Pharaoh's palace but not the homes of the Jews.
Many modern occurrences of localized but intense Paederus impact are documented in research papers with titles like "An outbreak of paederus dermatitis in a suburban hospital in Sri Lanka", "An outbreak of 268 cases of Paederus dermatitis in a toy-building factory in central China", "Outbreak of dermatitis linearis caused by Paederus ilsae and Paederus iliensis (Coleoptera: Staphylinidae) at a military base in Iraq", and "Evacuation of an Aboriginal community in response to an outbreak of blistering dermatitis induced by a beetle (Paederus australis)".