Sicariidae

Keyserling, 1880

Sixeyed Sicariid Spiders, recluse spiders, violin spiders, sand spiders, assassin spiders

Genus Guides

Loxosceles(Recluse Spiders)

Sicariidae is a of haplogyne spiders comprising three —Loxosceles, Sicarius, and Hexophthalma—with approximately 177-180 . Members are characterized by six arranged in three dyads (pairs), a distinctive trait among spiders. The family includes medically significant species such as the brown recluse (Loxosceles reclusa) and six-eyed sand spiders. All genera produce sphingomyelinase D or related tissue-destroying substances in their venom, unique among spiders. The family exhibits diverse ecological strategies: Loxosceles species are and found nearly worldwide in warmer regions, while Sicarius and Hexophthalma are specialized desert dwellers with self-burying .

Loxosceles rufescens by (c) Ludivine Lamare, some rights reserved (CC BY), uploaded by Ludivine Lamare. Used under a CC-BY license.

Loxosceles apachea by (c) Andrew Meeds, some rights reserved (CC BY), uploaded by Andrew Meeds. Used under a CC-BY license.

Loxosceles apachea by (c) Gordon C. Snelling, some rights reserved (CC BY), uploaded by Gordon C. Snelling. Used under a CC-BY license.

Pronunciation

How to pronounce Sicariidae: /sɪˈkæri.aɪˌdiː/

These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.

Identification

Positive identification requires examination of arrangement: six eyes in three dyads (pairs), unlike the eight eyes of most spiders. This pattern is shared only with Scytodidae (spitting spiders), from which Sicariidae differ by lacking the highly convex and spitting apparatus. Loxosceles may be distinguished from similar brown spiders by the eye pattern alone; the violin marking is variable and not diagnostic. Sicarius and Hexophthalma are recognized by their six-eyed pattern combined with crab-like appearance and desert . Molecular and genitalic examination is required for -level identification.

Images

Habitat

Highly variable across . Loxosceles occupies diverse including natural, urban, and domiciliary environments, with many records from caves and nearby areas. Sicarius and Hexophthalma are specialized for sandy desert environments, where they exhibit self-burying . In Brazil's Caatinga biome, Sicarius is found almost exclusively in this habitat with isolated records from Restinga, dry forest enclaves in Cerrado, and Atlantic Forest areas. Caves appear to be attractive habitats for , with some Loxosceles showing troglomorphic adaptations.

Distribution

Loxosceles distributed nearly worldwide in warmer regions; native range of L. reclusa centered in the central and southeastern United States (Texas to northern Georgia, southeast Nebraska, southwest Ohio). Mediterranean recluse (L. rufescens) introduced to many urban areas globally. Sicarius native to South and Central America, particularly Brazilian Caatinga. Hexophthalma restricted to southern African deserts. In Brazil's Bahia state, 14 confirmed across 48 municipalities, with the São Francisco River acting as a geographic barrier (>75% of species east side, ~20% exclusively west).

Diet

. Sicarius observed feeding on insects; laboratory specimens accept pomace flies (Drosophila) and crickets. Specific prey preferences otherwise poorly documented. Some Loxosceles species show cannibalistic .

Life Cycle

Long-lived spiders; Loxosceles individuals live 1.5-3 years in captivity, with some Sicarius and Hexophthalma living up to fifteen years—among the longest-lived spiders. Development includes , spiderling, and stages. Female Loxosceles produce egg sacs; clutch sizes and developmental rates vary by species.

Behavior

Reclusive, cryptic, and . Loxosceles constructs thin, haphazard, sheet-like webs in narrow cracks and crevices, under stones or objects. Sicarius and Hexophthalma exhibit self-burying , using legs and body to cover themselves with sand for ambush , becoming nearly invisible. Low vagility; often localized. Surprisingly tolerant of conspecifics, with large populations occupying small areas. Defensive rather than aggressive biting behavior.

Ecological Role

in their respective . Loxosceles serves as a predator in human-modified environments. Sicarius and Hexophthalma function as specialized ambush predators in desert . Specific ecosystem roles otherwise poorly documented.

Human Relevance

Medical significance due to necrotic venom containing sphingomyelinase D, capable of causing dermonecrotic , hemolysis, and rare effects. However, verified bites are uncommon and often misattributed; recluse spiders are reluctant to bite without significant provocation. No known antivenom exists. Misidentification is common, with many necrotic wounds actually caused by bacterial (e.g., MRSA) or other conditions. Public fear exceeds actual risk; media sensationalization has inflated their dangerous reputation.

Similar Taxa

Scytodidae (spitting spiders)Shares six in three dyads; distinguished by highly convex housing enlarged venom glands, spitting , and non-necrotic venom
Pholcidae (cellar spiders)Similar long-legged, sprawling appearance and web construction; distinguished by eight , different eye arrangement, and non-necrotic venom
HomalonychidaeSimilar cryptic, ground-dwelling habit and debris-encrusted appearance; distinguished by eight and lack of necrotic venom

Misconceptions

The dark violin-shaped marking on Loxosceles is often considered diagnostic but is variable and absent in some individuals; several unrelated spiders possess similar markings. Recluse spiders are frequently blamed for necrotic wounds in areas where they do not occur, and even where present, bites are rare and most do not produce severe . The belief that recluse spiders are aggressive is incorrect—they are defensive and reluctant to bite. In Florida, breeding proved scarce (only 19 of 220 investigated sites), and all were Mediterranean recluses rather than brown recluses.

More Details

Venom biochemistry

Sphingomyelinase D and related tissue-destroying substances are unique to Sicariidae among spiders, otherwise found only in certain pathogenic bacteria. This is responsible for dermonecrotic and hemolytic effects. Not all produce equally potent venom; some Neotropical Sicarius species lack significant dermonecrotic activity, while S. ornatus and S. thomisoides possess active sphingomyelinase D.

Taxonomic history

established by Keyserling in 1880; later treated as Loxoscelinae of 'Loxoscelidae' in 1893, though this violates nomenclatural priority rules. World Spider Catalog recognizes Loxoscelinae as a subfamily of Sicariidae. The African formerly in Sicarius were separated into revived Hexophthalma in 2017 based on phylogenetic study.

Cytogenetics

systems show diversity: most Sicariidae have multiple systems (X1X2Y, X1X20), but S. tropicus has a simple XY system—the first described for the . numbers range from 2n♂=18 to 2n♂=23.