The mainly tropical spider family Scytodidae (spitting spiders) includes 229 described species (Platnick 2014), just seven of which occur in North America north of Mexico (Ubick 2005). In the Nearctic, with the exception of Scytodes thoracica (a synanthrope with a worldwide distribution that includes eastern North America north to southeastern Canada), all species are strictly southern. Two of these, Scytodes fusca and Scytodes longipes, are pantropical and probably synanthropic. Another synanthrope, Scytodes globula, may be established in Florida (Guarisco 2003). The remaining three Nearctic scytodids, most of which have been recorded from Texas (Vogel 1970 cited in Ubick 2005), are probably Nearctic endemics (i.e., found only in this region).
Scytodids are six-eyed spiders (lacking the anterior median eyes), with three pairs of eyes forming a strongly recurved row (i.e., the lateral eyes are positioned farther back than the median eyes). Their legs are long and lack heavy spines.
Scytodids are unique among spiders in that at least some species capture prey by spitting strands of glue from their fangs. The glue is produced in an enlarged posterior (rear) lobe of the venom gland that occupies much of the cephalothorax (accounting for the convex shape of the carapace, the top of the cephalothorax).
A potential prey item is approached with a distinctive slow-walking behavior. When within range (a few centimeters), the spider raises its fangs and sprays its victim--extremely rapidly--with fine strands of glue, binding it to the substrate and immobilizing it. The fangs vibrate during spitting, resulting in a stream of glue that forms two zigzag lines covering a broad area (see Suter and Stratton 2009 for a biomechanical analysis of this process, including photographs). After spraying, the spider cautiously approaches and bites its prey, then retreats and waits, eventually returning to feed. Feeding occurs through one or several bite holes. (Bradley 2013)Bradley (2013) notes that finding small prey glued to a wall or ceiling by sticky silk lines is a clue that there are scytodids in the area. Although it is often asserted that scytodid glue is mixed with venom, this has been challenged by Clements and Li, who found no evidence of spray toxicity in experiments using Scytodes pallida and various prey types (Clements and Li 2005; Suter and Stratton 2009).
Many scytodids are synanthropic, occurring in and around human habitation. Some scytodids are wandering hunters, living on the ground, under rocks, and in leaf litter. Others build loose pholcid-like space-filling webs and may be communal (e.g., Miller 2006). Females lack cylindrical spigots on the spinnerets and thus do not construct a typical egg sac, instead binding the eggs with a few strands of silk and carrying them beneath the body. (Ubick 2005)
Ubick (2005) provides key taxonomic references for the Nearctic fauna and refers to several known undescribed scytodid species in this region.
(Ubick 2005; Bradley 2013)
Like the Sicariidae and Diguetidae these spiders are haplogyne (having less complex female genitalia), and have six eyes arranged in three pairs. The Scytodidae differ from the Sicariidae and Diguetidae in having a dome-shaped carapace and in their characteristic flecked pattern of spots.
Scytodidae catch their prey by spitting a fluid that congeals on contact into a venomous and sticky mass. Remarkably, though it is produced in venom glands in the chelicerae, the fluid contains both venom and spider silk in liquid form. The venom-impregnated silk both immobilizes and envenoms prey such as silverfish. In high-speed footage the spiders can be observed swaying from side to side as they "spit", catching the prey in a crisscrossed "Z" pattern; it is criss-crossed because each of the chelicerae emits half of the pattern. The spider usually strikes from a distance of 10–20 mm and the whole attack sequence is over in a little under 1/700th of a second. After making the capture, the spider typically bites the prey with venomous effect, and wraps it in the normal spider fashion with silk from the spinnerets.