Daddy-long-legs spider (Pholcus phalangioides)

Physical characteristics

Adults have a compact, soft abdomen and a body length usually under 10 mm (females can reach about 9 mm; males are typically slightly smaller). Legs are proportionally long — often five to six times the body length — giving the spider a delicate, spidery appearance. Eye number and arrangement vary among pholcids but are reduced compared with many other spiders. Coloration ranges from pale grey to light brown with subtle patterning on the abdomen.

Behavior and diet

Pholcus phalangioides builds loose, irregular webs in sheltered, undisturbed places. When threatened the spider commonly vibrates its web rapidly; this defensive motion helps to blur the spider's outline and may confuse predators. Its diet is opportunistic and includes flies, mosquitoes, small insects and other spiders; it is notable for capturing and immobilizing larger spiders by chewing and entangling them in silk. Cannibalism can occur when food is scarce.

Reproduction and life cycle

Females carry an egg sac that typically contains a few dozen eggs. Instead of permanently affixing the sac to silk, the female may hold it near her jaws or keep it close to her body until the spiderlings hatch. Young spiders are translucent with shorter legs and pass through multiple molts (commonly five or six) before reaching maturity. In temperate indoor environments they may breed year-round.

Distribution, habitat and origin

Although probably of tropical origin, P. phalangioides is now cosmopolitan and commonly synanthropic — it spreads easily with human activity and establishes in houses, cellars, garages and caves around the world. It prefers stable, sheltered microhabitats where webs are undisturbed and prey is available.

Relationship with people and misconceptions

These spiders are generally harmless to humans and are often considered beneficial because they consume pest insects and other spiders. A persistent urban myth claims that "daddy-long-legs" are extremely venomous but cannot bite people; this confusion mixes different animals and is not supported by scientific evidence. Pholcid bites on humans are rare and, if they occur, typically produce little or no noticeable effect.

Similar species and distinctions

Several other long-legged pholcid species resemble P. phalangioides, including Crossopriza lyoni and Physocyclus globosus. It is important to distinguish true spiders (order Araneae) like pholcids from harvestmen (order Opiliones) and from non-arachnid insects sometimes called daddy long-legs. For an overview of the family classification see Pholcidae.

• Notable traits: very long legs, loose webs, web-vibrating defense.
• Typical habitat: ceilings, attics, basements, caves, and sheltered outdoors sites.
• Role: predator of small arthropods and other spiders; largely harmless to humans.