Holocnemus pluchei

Distinguished from the similar Pholcus phalangioides (Long-bodied Cellar Spider) by its more dome-shaped web structure and preference for outdoor, sun-shaded locations rather than dark indoor spaces. The black and white banding on leg joints is distinctive. Females can be identified by the projecting sternum and swollen pedipalps. Both sexes possess stridulatory organs, unlike most spiders where only males have such structures.

Small-bodied spider with extremely long, fragile legs that make it appear much larger than its actual size. Body length 5–7.5 mm (females slightly larger than males). Legs display distinctive black and white circles around the joints. Immature individuals resemble adults in general form. Females possess swollen pedipalps and a projecting sternum, the latter thought to function in mate selection.

Builds webs in shaded outdoor locations such as under building overhangs, among dense vegetation, and in the leathery leaves of agave plants. In its native Mediterranean range and introduced North American populations, it is often found in warmer, sheltered microhabitats. Unlike many cellar spiders, it is more common outdoors than indoors in arid regions like southern Arizona, though it will occupy basements, attics, and eaves of buildings.

Native to the Mediterranean region of Europe and North Africa. Introduced to North America with earliest record from Sutter County, California in 1974; now ranges east to central Texas and north to southern Oregon. Also introduced to southern Western Australia, Argentina, and Japan. Present in urban and suburban environments across its introduced range.

Preys on various insects including fruit flies (Drosophila), house flies (Musca domestica), and damselflies. In group webs, the largest individual that detects prey captures it approximately 80% of the time. Food availability directly affects development rate and adult size.

Spiderlings emerge from eggs and undergo five molts during development; females more likely to undergo a sixth molt than males, and poorly fed individuals more likely to undergo additional molts. Spiderlings at 4–5 days old choose whether to join group webs or build solitary webs. Females carry egg sacs in their fangs and guard them until hatching, during which time they do not feed. Each brood contains approximately 50 spiderlings. Females may produce multiple clutches, sometimes as soon as two months after hatching the first brood. Laboratory-reared individuals may live up to one year.

Exhibits two primary web types: curved prey-capture sheets and dome-shaped webs constructed by egg-carrying females that completely surround the female and eggs. Individuals frequently relocate to new webs throughout their lifespan. When disturbed, performs 'bouncing'—rapid vertical movement while keeping legs on the silk—to dislodge intruders. Both sexes stridulate by rubbing pedipalps against chelicerae; female stridulation appears associated with unreceptivity to male advances. Males aggressively steal food from females' webs rather than exhibiting 'chivalrous' prey-sharing behavior seen in other pholcids. Group-living individuals compete for prey through display and fighting, with conflicts occasionally escalating to death when spiders are similar in size.

Serves as prey for jumping spiders (Salticidae), particularly Portia fimbriata and Portia labiata, which employ aggressive mimicry to avoid triggering defensive bouncing. Functions as a generalist insect predator in urban and suburban ecosystems. Group living reduces individual silk production costs but increases intraspecific competition for food resources.

Considered a common household spider and urban pest. Not dangerous to humans due to inability to deliver a strong bite, though venom is present. Has been documented as a source of arginine kinase, an allergen that triggered asthma in at least one documented case. Often mistaken for the brown recluse spider, leading to unnecessary killing.

• Pholcus phalangioidesSimilar long-legged appearance and web-building behavior; distinguished by preference for dark indoor spaces and less dome-shaped web structure
• Holocnemus caudatusCongeneric species found in Spain and Sicily; geographic separation aids identification
• Holocnemus hispanicusCongeneric species found in Spain; geographic separation aids identification

Often mistaken for the brown recluse spider (Loxosceles reclusa) due to similar habitat use, leading to misidentification and unnecessary killing. Despite common name 'daddy long-legs,' it is not a harvestman (Opiliones) and does not possess the mythically exaggerated venom potency sometimes attributed to that group.

• spider
• Pholcidae
• introduced species
• group living
• stridulation
• urban pest
• allergen

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Bug Eric: Spider Sunday: Marbled Cellar Spider
• Bug Eric: July 2011
• Anti‐predator defences of a web‐building spider, Holocnemus pluchei (Araneae, Pholcidae)
• Food Level and Life History Characteristics in a Pholcid Spider (Holocnemus Pluchei)
• Predator‐prey interactions between web‐invading jumping spiders and a web‐building spider, Holocnemus pluchei (Araneae, Pholcidae)