Tree trunk spider Temporal range: Cretaceous–present PreꞒ Ꞓ O S D C P T J K Pg N
Male Hersilia okinawaensis
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Chelicerata
Class:	Arachnida
Order:	Araneae
Infraorder:	Araneomorphae
Family:	Hersiliidae Thorell, 1869
Diversity
16 genera, 206 species

Hersiliidae is a tropical and subtropical family of spiders first described by Tamerlan Thorell in 1869,^[1] which are commonly known as tree trunk spiders. They have two prominent spinnerets that are almost as long as their abdomen, earning them another nickname, the "two-tailed spiders". They range in size from 10 to 18 mm (0.4 to 0.7 in) long. Rather than using a web that captures prey directly, they lay a light coating of threads over an area of tree bark and wait for an insect to stray onto the patch. When this happens, they encircle their spinnerets around their prey while casting silk on it. When the insect is immobilized, they can bite it through the shroud.

Diversity

Hersiliidae is an entelegyne family (characterized primarily by the nature of the female genital system), and together with the family Oecobiidae traditionally formed the superfamily Oecobioidea.^[2] The family consists of about 206 species divided into sixteen genera.^[3] It has a global distribution in tropical and subtropical regions, with only a few species being found north of the 40°N parallel. All members are ecribellate (lack the cribella or perforated plates which produce multiple, exceptionally fine strands of silk) and are recognizable by the pair of exceptionally long spinnerets set at the tip of the abdomen.^[2] They have eight eyes, set in two curved rows. They are small to medium-sized spiders and are active day and night. They are very well camouflaged when stationary on the trunk of a tree and aligned with the bark markings.^[4]

Genera

As of April 2019^[update], the World Spider Catalog accepts the following genera:^[3]

Extinct genera

• †Burmesiola Wunderlich 2011 Burmese amber, Myanmar, Cenomanian
• †Fictotama Petrunkevitch 1963 Dominican amber, Miocene
• †Gerdia Menge 1869 Baltic amber, Eocene
• †Gerdiopsis Wunderlich 2004 Baltic amber, Eocene
• †Gerdiorum Wunderlich 2004 Baltic amber, Eocene

Gallery

• 
  A Hersilia species immobilizing a cicada
• 
  Injecting venom through the shroud
• 
  Fully immobilized the cicada