|
Family: Scytodidae (spitting spiders)
Life
> Eukaryotes
>
Opisthokonta >
Metazoa
(animals) > Bilateria > Ecdysozoa > Panarthropoda > Tritocerebra >
Arthropoda > Arachnomorpha > Cheliceriformes > Chelicerata > Euchelicerata
> Arachnida > Araneae
> Araneomorpha
The only genus of this family, Scytodes,
can be regarded as the stealth fighter of spiders and is commonly called the
spitting spider and is harmless to humans. Previously Scytodes was
included in the same family as Loxosceles (violin spider,
Sicariidae) and Drymusa (False
Violin spider, Drymusidae). Scytodes is harmless, unlike Loxosceles
which is venomous to humans).
Locally, this spider has abandoned a sedentary web life,
unlike those in tropical regions, and instead roams nocturnally and actively
hunts its prey. It can be found under bark, leaf-litter and sometimes in the
home. There are 28 species known from South Africa and this genus has a
worldwide distribution. Three cosmopolitan species can be found to inhabit dark
recesses in homes.
Scytodes is derived from the greek "skytos" meanig
"leather-like".
It is a small spider, about 5-9mm in length. It is shiny
and glabrous (hairless) but with a scattering of short setae over the body and
the base colour is mid-brown with darker symmetrical patterning of stripes and
spots The thin legs are banded. It has a distinctive shape with a domed,
oversized prosoma (a diagnostic feature of Scytodes) which houses an
anterior venom gland that is connected to a posterior section that synthesises a
sticky silk used for defence and prey capture.
Scytodes is a nocturnal wanderer with poor vision
and roams around with front legs raised to detect prey using long trichobothria
(sensory hairs) on the metatarsi (second last apical segment of the foot). Once
prey such as fish moths, moths, flies etc. is detected, it proceeds with such
stealth that it goes unnoticed by its prey. Once within a range of up to 5-10mm,
it ejects 2 streams of very sticky synthesized silk over its prey, gluing it to
the substrate. In this rapid event (lasting about 140 milliseconds) the silk is
ejected a distance of 15-20mm through the rapid contractions of large prosomal
muscles. It appears that the victim is paralysed by a venomous component in the
silk. The spider then advances and bites a leg of the prey and once dead, it is
removed from its bonds dragged off to a safe retreat to be sucked dry leaving
the empty remains. Prey capture has been well documented and two rows of
horizontal zig-zag oscillations of silk have been described. However, in the
Cape Town area, vertical oscillation has been observed with Scytodes testudo.
It is not known if different methods are used randomly by all species or if the
methods are species specific.
Unlike most spiders, Scytodes is quite long lived,
being known to live from 2 to 4 years. After laying, the eggs are held together
with a few strands of silk and carried around by the female in her chelicerae
(fangs) although Bristow states that it is attached to the spinnerets and held
with the palps leaving the chelicerae free for prey capture. Some species use a
lace-like covering for the eggs. Eggs hatch about 2 weeks after laying and
emerge 2 weeks later.
Text by Norman Larsen © |
