Crossopriza lyoni is a widespread species of cellar spiders that prefer to live in or around human structures.

They are a regulated species in some countries and are often regarded as pests due to the large amounts of unsightly webs they construct inside human homes.

C. lyoni and other cellar spiders are also often confused with two other invertebrates - the harvestmen (order Opiliones) and the crane flies (family Tipulidae) - both of which are also known as 'daddy longlegs'.

[5][6] The species was first formally described in 1867 by the British naturalist John Blackwall from a collection of spiders from Meerut, Agra, and Delhi.

The legs are gray to amber in color and covered with numerous small longitudinal brown spots.

In the middle of the upper surface is a deep depression (called the thoracic fovea) and a darker longitudinal band of color.

The abdomen (the opisthosoma) is gray with white lateral stripes and various dark and light patches on the sides and the upper surface.

The spiders rub these structures with a matching pair of sclerotized plates at the anterior portion of the abdomen, producing sound.

They also possess stridulatory files (in the form of a series of small ridges) on their chelicerae which are rubbed against the pedipalps to produce sound.

[10] C. lyoni can be distinguished from other members of the genus through several ways: by the characteristic boxy shape of their abdomens (C. cylindrogaster has a cylindrical abdomen); by the presence of two apophyses (jutting structures) in the chelicerae of males (C. pristina, C. semicaudata, and C. soudanensis all possess only one apophysis on each chelicera);[10] or simply by geographic distribution (C. lyoni can be found globally and is the only species of Crossopriza in the New World, while the other species like C. johncloudsleyi and C. nigrescens are restricted to Africa or the Middle East).

Mating is accomplished with the male inserting both his pedipalps into the genital orifice of the female and transferring a previously prepared packet of sperm into her spermathecae.

They then clutch the resulting egg sacs with their mouthparts and carry them around (a behavior common among all cellar spiders).

[13] C. lyoni, like other cellar spiders, will violently gyrate their bodies in small circles when threatened.

They usually build large irregular webs in corners of rooms, basements, cellars, and beneath ceilings.

[4][21] As a result, C.lyoni has been introduced to most of the world, including Australia, Asia,[22] Africa,[23] Europe,[24][25] North and South America, and some Pacific islands.

[10][26] Their place of origin is unknown but have been variously posited to be Africa (where their genus has the highest diversity) or somewhere in Asia.

[9][27][28] While doing no appreciable damage to humans, they are sometimes regarded as pests due to the large amounts of unattractive webs they construct inside houses.

Sealing small entry points can also prevent both insect and spider access into the house.

In areas where mosquito-borne diseases (like dengue fever) are present, it is recommended to avoid removing natural populations of C.

[23] Studies have also shown that C. lyoni spiders that eat dengue virus-infected mosquitoes do not seem to acquire the virus themselves.

[13] A study in 2009 showed that the webs of C. lyoni exhibit antibacterial properties against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and others.

[31] C. lyoni and other pholcids are often the subject of a popular urban legend about how they are the most venomous known animals except that 'their fangs are too small to penetrate human skin'.