The Mediterranean recluse spider (''Loxosceles rufescens'') is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

spider Spiders (order (biology), order Araneae) are air-breathing arthropods that have eight limbs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude spider silk, silk. They are the largest order of arachnids and ran ...

that originated in the Mediterranean region as its name implies, but can now be found in many parts of the world and is listed as one of the most invasive spiders worldwide. Usually dwelling in

cave Caves or caverns are natural voids under the Earth's Planetary surface, surface. Caves often form by the weathering of rock and often extend deep underground. Exogene caves are smaller openings that extend a relatively short distance undergrou ...

s, the spiders will also inhabit basements and tunnels. Their webs shelter their egg sacs, which hatch into young that molt as they grow. The spider hunts at night and eats species including

silverfish The silverfish (''Lepisma saccharinum'') is a species of small, primitive, wingless insect in the order Zygentoma (formerly Thysanura). Its common name derives from the insect's silvery light grey colour, combined with the fish-like appearanc ...

and

cockroaches Cockroaches (or roaches) are insects belonging to the Order (biology), order Blattodea (Blattaria). About 30 cockroach species out of 4,600 are associated with human habitats. Some species are well-known Pest (organism), pests. Modern cockro ...

, and they usually target smaller insects. Similar to other species in their genus, bites from ''L. rufescens'' can cause necrosis and, for some individuals, systemic damage due to the enzyme

sphingomyelinase D Sphingomyelin phosphodiesterase D (EC 3.1.4.41, sphingomyelinase D) is an enzyme of the sphingomyelin phosphodiesterase family with systematic name sphingomyelin ceramide-phosphohydrolase. These enzymes catalyse the hydrolysis of sphingomyelin, r ...

. Pest control may be undertaken with similar strategies as used for the

brown recluse spider The brown recluse (''Loxosceles reclusa'', Sicariidae, formerly placed in a family "Loxoscelidae") is a recluse spider with necrotic venom. Similar to those of other recluse spiders, their bites sometimes require medical attention. The brown ...

Characteristics

''L. rufescens'' is a cave-dwelling arachnid that is nearly indistinguishable in appearance from ''Loxosceles reclusa'', the

. Individuals can be identified as medium-sized spiders distinguished by three pairs of two eyes organized in the shape of a triangle (spiders commonly have eight eyes), with a violin-shaped pattern on their cephalothorax. This spider belongs to the genus ''Loxosceles'' which contains many of the most dangerous spiders in the world. Both males and females grow to approximately 7–7.5 mm in length. ''L. rufescens'' egg sacs contain approximately 40 eggs that each take a few weeks to hatch, depending on the temperature. The young spiders grow slowly and produce molts during their growing phase. These molts often have a pale ghostly appearance. Mediterranean recluse spiders typically live from one to three years. The webs of Mediterranean recluse spiders spin function as a daytime hiding spot and provide seclusion for the egg sacs. The webs are very thin and fragile, formed by strands of silk laid in a disorganized manner.

Distribution and habitat

The Mediterranean recluse is listed as one of the most invasive species in the world. It is native to the Mediterranean area and

western Asia West Asia (also called Western Asia or Southwest Asia) is the westernmost region of Asia. As defined by most academics, UN bodies and other institutions, the subregion consists of Anatolia, the Arabian Peninsula, Iran, Mesopotamia, the Armenian ...

, including parts of Europe and Northern Africa, and prefers warm temperatures and generally dry weather. Today, this spider has a global distribution due to increased human travel and the increase of transported goods. This species has been introduced to

Madagascar Madagascar, officially the Republic of Madagascar, is an island country that includes the island of Madagascar and numerous smaller peripheral islands. Lying off the southeastern coast of Africa, it is the world's List of islands by area, f ...

, southeast Asia from India to Japan, Australia, and numerous Atlantic and Pacific islands (including four in the Hawaiian archipelago) and in North America, it has been recorded in over 20 of the United States, widely scattered from California to Florida and north to Michigan, as well as Ontario, Canada. In areas where ''L. rufescens'' are non-native, they can be found in semi-arid environments and damp areas such as basements, caves, and tunnels. In these locations, individuals can find their favorable meal of cockroaches and silverfish. During a routine building pest check-in in 2021, spiders of this species were found in the basement of the

University of Michigan The University of Michigan (U-M, U of M, or Michigan) is a public university, public research university in Ann Arbor, Michigan, United States. Founded in 1817, it is the oldest institution of higher education in the state. The University of Mi ...

's Shapiro Undergraduate Library, which led to its closure for two days.

Ecology

''L. rufescens'' differs from many other spider species in their predatory behavior. ''L. rufescens'' is an active hunter and will set out at night to capture and kill a variety of arthropods that are susceptible to their venom rather than catching them in a web. They are most active at night and typically target smaller insects because of their vulnerable soft

exoskeleton An exoskeleton () . is a skeleton that is on the exterior of an animal in the form of hardened integument, which both supports the body's shape and protects the internal organs, in contrast to an internal endoskeleton (e.g. human skeleton, that ...

. Males are more prolific hunters than female individuals partly due to their simultaneous search for a potential mate.

Threat to humans

Spiders in the genus ''Loxosceles'' are well known for their bite, causing skin necrosis and for some people, causing great damage and widespread, systemic effects. This is referred to as loxoscelism. The necrosis is due to the unique enzyme,

(SMase D). This enzyme from the ''Loxesceles'' venom alters the structure of the membrane raft, leading to protease activation on the membrane. This ultimately results in proteolytic cleavage of cell surface proteins and necrosis of the cell. Most cases are medically insignificant, but in some cases, from 2 to 8 hours after a bite, there may be penetrating pain followed by a burning sensation. Areas adjacent to the bite often become red and painful due to vasospasm and ischemia. A blister may form which often changes to a dark blue color with a sunken center days following the bite. In rare cases, hemolysis, intravascular coagulation, and thrombocytopenia can occur, leading to renal failure. In 2024, ''L. rufescens'' has been blamed for the deaths of two individuals in Italy; one a 52-year-old policeman from Palermo, bitten by ''L. rufescens,'' according to a local Sardinian newspaper, and the other a 23-year old male, who died more than a month after being bitten, according to ANSA (Agenzia Nazionale Stampa Associata), the "National Associated Press Agency".

Control and mitigation

Controlling ''Loxosceles'' species populations within dwellings can be challenging as they prefer to dwell in small, dark crevices. This is exacerbated by their ability to survive without food and water for extended periods. There are no published control or mitigation efforts specifically directed to the Mediterranean recluse spider population, except for the mention of the need for further such efforts in a study conducted in

Washington, D.C. Washington, D.C., formally the District of Columbia and commonly known as Washington or D.C., is the capital city and federal district of the United States. The city is on the Potomac River, across from Virginia, and shares land borders with ...

However, with the indistinguishable features between the brown recluse and Mediterranean recluse spiders, efforts to control the brown recluse spider may be translated into mitigating the Mediterranean recluse population. Many of these efforts may include regular pest control and vacuuming of dead insects, sanitizing, removal of spider webs, and the use of glue traps and insecticides.

Gallery

File:Loxosceles rufescens juvenile in Rijeka, Croatia 01.jpg, Juvenile specimen File:Loxosceles rufescens juvenile in Rijeka, Croatia 02.jpg, ''L. rufescens'' with prey ( moth fly) File:Loxosceles rufescens in Rijeka, Croatia.jpg, Specimen from Croatia File:Loxosceles rufescens 04.jpg

References

External links

{{Taxonbar, from=Q2301444 Sicariidae Cosmopolitan spiders