Fam. 21. Pholcidae.—This is another very well-marked family. The most striking peculiarity of its members is the possession of extremely long and thin legs, the metatarsi being especially elongated, and the tarsi furnished with several false articulations.
The eyes are also very characteristic. They are usually eight in number, the two anterior median eyes being black, while the other six are white, and arranged in lateral groups of three, sometimes on prominences or stalks. The abdomen is sometimes nearly globular, but more often long and cylindrical. Most of the genera, which, including several new genera lately established by Simon, number more than twenty, are poor in species, but enjoy a very wide distribution. This is explained by the fact that many of them live in cellars and outhouses. This is the case with the genus Pholcus, of which the sole English species Ph. phalangioides is a perfect nuisance in buildings in the most southern parts of the country, “spinning large sheets of irregular webs in the corners and angles, and adding to them year by year.”[[315]] Other genera are Artema (Africa, South Asia, Polynesia, America), which includes the largest examples, and Spermophora, a six-eyed genus whose few species are widely distributed.
Fam. 22. Theridiidae.—Sedentary spiders, usually with feeble chelicerae and relatively large abdomen. Snare irregular.
The Theridiidae, as here understood, are a very extensive family, and more than half the British spiders (about 270 species) are included within it. This family and the next present unusual difficulties of treatment, and there is great divergence of opinion as to the most satisfactory way of dealing with them. This is chiefly due to the fact that, notwithstanding an infinite variation of facies, important points of structure are wonderfully uniform throughout both the two groups, while any differences that do occur are bridged over by intermediate forms which merge into each other.
Simon[[316]] has become so impressed with the difficulty of drawing any clear line between certain groups which he previously classed under the Theridiidae and the spiders commonly known as Epeiridae, that he has recently removed them from the Theridiidae and united them with the orb-weaving spiders to form the Family Argiopidae, the family name Epeiridae being discarded. The groups which, in his view, belong to the Argiopidae will be indicated below. This view has not met with universal acceptance, and notwithstanding the undoubted difficulty of clearly distinguishing between the two families, it is more convenient in the present work to maintain as a separate family a group of spiders nearly all of whose members possess the easily recognised characteristic of spinning a circular snare.
The Theridiidae and the Epeiridae form the great bulk of the sedentary spiders. They do not wander in search of prey, but sit in snares of various structure and wait for their victims to entangle themselves. The spinnerets, organs whose peculiarities are often strongly marked in other families, are here wonderfully constant in their arrangement and general appearance, forming a compact rosette-like group beneath the abdomen. Their eyes, normally eight in number, present an infinite variety of arrangement. Their chelicerae and mouth-parts vary considerably, but no abruptness of variation is distinguishable. This is unsatisfactory from a systematic point of view, and the necessary result is that certain groups might with equal propriety be classed with the Theridiidae or the Epeiridae. The latter family will here be taken as including all the orb-weaving spiders and a few groups which appear inseparable from them.
We shall consider the Theridiidae as comprising the seven sub-families, Argyrodinae, Episininae, Theridioninae, Phoroncidiinae, Erigoninae, Formicinae, and Linyphiinae, and shall briefly deal with them in this order.
(i.) The Argyrodinae are very curious spiders with very long and often flexible abdomen. They are commonly parasitic on the circular snares of Epeirid spiders, between the rays of which they spin their own irregular webs. There are three genera, Argyrodes, Ariamnes, and Rhomphaea, which are distributed in the tropical and sub-tropical regions all over the world.
(ii.) The Episininae hardly conform to the character of sedentary spiders, being frequently found outside their webs. In most species the abdomen is narrow in front and broader behind, where it is abruptly truncated or bluntly pointed. The genus Episinus is widely distributed, and one species, E. truncatus, is one of our most peculiar English spiders. It occurs occasionally under ledges of grassy or heathery banks. The genus Tomoxena is an inhabitant of tropical Asia. Janulus is found in the same regions, and in tropical America.
(iii.) The Theridioninae are a large group of spiders, often very ornate, and spinning snares of irregular threads running in all directions. The abdomen is usually more or less globular. The chelicerae are small and weak, and the paturon is transversely (not obliquely) truncated for the reception of the small unguis or fang. The somewhat long thin legs are almost or entirely destitute of spines.