Scytodes thoracica

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Geographic Range

Members of the genus Scytodes are predominately tropical or subtropical spiders. However, spitting spiders are found scattered across neartic, paleartic, and neotropical regions. This species is commonly found in the eastern United States, as well as in Britain, Sweden and other European countries. Specimens have also been found in Japan and Argentina. It is unclear which populations are native and which are introduced in these regions. The presence of this species in more northern climates is attributed to the availability of warm houses and buildings, to which these spiders have adapted. ("The Spider Book", 1912; Emerton, 1902; Kaston, 1972; "Scytodes thoracica (Spitting spider)", 2011; Ubick, et al., 2005)

Habitat

Spitting spiders are found in temperate forests. When associated with humans, they are most commonly found in dark corners, cellars, cupboards, and closets of houses and other buildings. ("Spitting spider Scytodes thoracica", 2012)

  • Average elevation
    Sea Level m
    ft

Physical Description

This species has long, thin, legs, and are glabrous (hairless), with the exception of short sensory setae scattered over the body. These spiders are also easily identified by their oversized cephalothorax (prosoma), which slopes upward towards their posterior ends. Their abdomens (which are roughly the same circular shape as the cephalothorax) slope downwards and are only slightly smaller than the cephalothorax. Like all spiders, these two body tagmata (segments) are separated by a thin pedicel (waist-like connector). (Emerton, 1902; Goethals, 1997; Kaston, 1972; Larsen, 2005; Robinson, 2005)

Large, well-developed poison glands are located in the cephalothorax. These glands are divided into two parts: a smaller, anterior compartment which stores venom and a larger, posterior compartment which contains a mucilaginous substance. These spiders produce a gummy substance which is a mix of the two substances and is excreted by their fused chelicerae, which can not be moved separately. Scytodes are ecribellate, lacking the silk-spinning organ (cribellum) of some other spiders. They have a single tracheal spiracle. (Emerton, 1902; Goethals, 1997; Kaston, 1972; Robinson, 2005)

Spitting spiders have pale yellow bodies with black speckled markings on the cephalothorax, which slightly resemble a lyre. Their legs, which slowly taper in size as they extend from their bodies, are long with black bands. The most anterior portion of the head, below the eyes, projects forwards, past the mandibles. This species exhibits sexual dimorphism, with males typically ranging from 3.5-4 mm in length and females ranging from 4-5.5 mm. (Emerton, 1902; Gertsch, 1949; Goethals, 1997; Kaston, 1972; Robinson, 2005)

  • Sexual Dimorphism
  • female larger
  • Range length
    3.5 to 5.5 mm
    0.14 to 0.22 in

Development

All spiders reproduce sexually, and sex is determined by meiosis. Following copulation and egg fertilization, females lay eggs in a cocoon carried under their bodies for 2-3 weeks until eggs hatch. Spiderlings remain with their mothers until their first molts and then disperse to live solitary lives, reaching adulthood after 5-7 molts. It can take 2-3 years for females to reach maturity. ("Spitting spider Scytodes thoracica", 2012; Gertsch, 1949; Guarisco, 1991; Koh, et al., 2009; Larsen, 2005)

Reproduction

Spitting spiders are solitary, interacting only during mating. These spiders are aggressive hunters, so males must approach females cautiously or else be mistaken for prey. Both sexes produce pheromones, which are detected through contact with chemosensory hairs covering the pedipalps and first pair of legs; female mate choice is based on male pheromone production. Location of mates is not based on visual cues and mating usually occurs following an accidental meeting of a male and female. Upon meeting a female, male spitting spiders fill their palpal organs (accessory reproductive parts on the ends of each pedipalp) with sperm. They do this by drawing a sperm web across their genital openings to accumulate sperm droplets, using their third pair of legs. In Scytodes, the sperm web is a single thread which typically takes a triangular shape. From there, sperm droplets are drawn into the palpal organ (bulb). Males approach females anteriorly; females raise their cephalothoraxes to allow males to insert both palpal organs into their genital opening. Sperm is then deposited and stored in females' seminal receptacles. After mating, the pair separates immediately. Males and females have multiple partners throughout their lifetimes. ("Spitting spider Scytodes thoracica", 2012; Foelix, 1982; Koh, et al., 2009; Sebeok, 1977)

Spitting spiders are dioecious and females require 2-3 years to reach maturity. Most mating occurs in the warmer months (especially August) but these spiders can expand their breeding seasons when living in warm areas, such as within homes. Sperm can be stored by females for months until eggs are laid. Compared to most spiders, spitting spiders lay relatively few eggs (20-35 eggs per cocoon) and 2-3 cocoons are typically produced by a female each year. This species displays maternal care both before (females carry egg cocoons) and after hatching, with newly hatched juveniles remaining with their mother until their first molts. Speed of growth and, therefore, rate of molting, is closely related to availability of prey and so the time that juveniles remain with their mother, as well as the age at which males reach maturity, is widely variable. These spiders can mate multiple times and usually die of hunger, exhaustion, or predation. (Koh, et al., 2009; Ramel, 2011; Suter and Stratton, 2011)

  • Breeding interval
    This species breeds 2-3 times a year.
  • Breeding season
    These spiders breed during warmer summer months.
  • Range number of offspring
    20 to 35
  • Average number of offspring
    28
  • Average age at sexual or reproductive maturity (female)
    2-3 years

Female spitting spiders exhibit parental care. They do not make nests or suspend cocoons in webs or other structures, but instead lay eggs in a cocoon that they carry either under their bodies or in their chelicerae. Females are more vulnerable to predation during this egg-carrying period, as they are unable to feed or defend themselves by spitting. Eggs typically hatch 2-3 weeks after being laid and nymphs (juveniles) remain with their mothers until their first molts. On occasion, females consume egg sacs that have resulted from mating with non-preferred males or contain defective eggs. Males display no parental investment after mating. (Koh, et al., 2009; Larsen, 2005)

  • Parental Investment
  • female parental care
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • protecting
      • female
  • pre-weaning/fledging
    • protecting
      • female
  • pre-independence
    • protecting
      • female

Lifespan/Longevity

Spitting spiders have a relatively long life span as they do not die following mating; males live 1.5-2 years and females live 2-4 years. Females may be preyed upon during their egg-carrying periods, while males often die of hunger and exhaustion while searching for and courting females. (Guarisco, 1991; Larsen, 2005; Ramel, 2011)

  • Range lifespan
    Status: wild
    1.5 to 4 years
  • Average lifespan
    Status: wild
    2.5 years

Behavior

Spitting spiders are primarily nocturnal. They are wandering and solitary spiders that actively hunt their prey and, due to their long, thin legs, are slow moving. They have extremely poor eyesight and therefore walk around with their front legs, which are covered with sensory setae, held up in order to sense their environments. ("Spitting Spider", 2004; Suter and Stratton, 2005)

When these spiders come into contact with prey, their attacks usually proceed in the following order: tapping of the front legs, spitting, biting, wrapping, and then feeding. When a spider contacts a prey item, it orients itself towards the prey and slowly taps its front legs until the prey is centered between them. It then spits a string of a gluey, venomous substance at the prey, covering it in 5-17 parallel, overlapping bands. The material can travel at a rate of up to 28 m/s and the pattern of the bands is produced as the spider lifts its chelicerae and oscillates its fangs during expulsion. The spider then quickly approaches its prey and uses its first and second pairs of legs to further entangle the prey in the drying glue, silk and venom. The venomous glue paralyzes the prey and, once it is dry, the spider bites its victim, injecting venom to liquify its tissues. It then grooms its first two sets of legs, cleaning any remaining glue, before drawing the prey into its chelicerae using its pedipalps. The spider holds the prey with its third legs and wraps it in silk produced by spinnerets. It then consumes its prey by sucking up the dissolved tissues. These spiders also use their spitting "web" as a defensive measure against other spiders or threats. ("Spitting Spider", 2004; Suter and Stratton, 2005; Suter and Stratton, 2011)

  • Range territory size
    1 to 35 m^2

Home Range

Spitting spiders will typically wander within a territory 30-35 m in size. ("Spitting Spider", 2004)

Communication and Perception

Although they can see, these spiders do not rely on vision for mate or prey recognition due to their poor eyesight. However, like most spiders, they use chemical signals to detect and respond to predators, prey, and mates. Spitting spiders use their raised front legs to detect prey and their environment using trichobothria (sensory hairs) on the metatarsi (second to last segment of the leg). These sensory hairs also contain chemoreceptors, which are sensitive to pheromones. Scytodes are also known to employ both acoustic and vibrational communication by tapping on the ground with their first pair of legs. (Koh, et al., 2009; Sebeok, 1977)

Food Habits

Scytodes are active nocturnal wanderers, not web-spinners. They are insectivores and when living indoors, they mostly eat other insects and arthropods, such as moths (Order Lepidoptera), Flies (Order Diptera), other spiders (Order Araneae), and household bugs (Order Heteroptera). When living outdoors, they eat similar food items and, in the Philippines, are known to eat insects such as green scale (Coccus viridis), black citrus aphids (Toxoptera aurantii), citrus mealybugs (Planococcus citri), Philippine katydids (Phaneroptera furcifera) and lime swallowtails (Papilio demoleus). In Britain, mosquitos (Family Culicidae) are often eaten. Many of their prey items are significantly larger than these spiders. Females may also occasionally consume their own egg sacs. ("Spider Fauna in Philippine citrus and their note as predator in the control of insect", 1989; "Spitting Spider", 2004; Gertsch, 1949; Gilbert and Rayor, 1985; Larsen, 2005; Medlock and Snow, 2008)

  • Animal Foods
  • insects

Predation

Since spitting spiders are slow moving, they use their spitting apparatus against predators, rather than attempting to flee. Indoors, the majority of its predators are household arthropods such as other spiders and centipedes, and may include mammals such as domestic cats. In the wild, spitting spiders may be prey for bats, toads, birds, and shrews. Additionally, humans play a major factor in controlling populations of this species through pest control. (Atkinson, 2002; Bristowe, 1941; Suter and Stratton, 2005)

Ecosystem Roles

When associated with humans, this spider's largest ecosystem role is in the control of insect populations, mostly of household pest species. They also serve as food for house centipedes (Scutigera coleoptrata) and other arthropod carnivores found in homes. In the wild, they may be preyed upon by a number of other species. (Gertsch, 1949; Kaston, 1948)

Economic Importance for Humans: Positive

This species contributes to the disposal of household pest insects and could potentially save homeowners money on investing in other methods of pest control. (Bristowe, 1941; Gertsch, 1949)

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

Though this species plays a role in controlling insect populations, it may also be considered a household pest. Many home-owners invest in pest-control in order to exterminate these spiders. Additionally, this spider is venomous, although its chelicerae, or fangs, are too small to pierce human flesh. (Bristowe, 1941; Gertsch, 1949)

  • Negative Impacts
  • household pest

Conservation Status

This species is a common house spider of the United States. It is less commonly found in Europe, Argentina, and Japan, but its conservation status is not a concern. ("Spitting Spider", 2004)

Contributors

Jacqueline Brand (author), University of Michigan-Ann Arbor, Jeremy Wright (editor), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

delayed fertilization

a substantial delay (longer than the minimum time required for sperm to travel to the egg) takes place between copulation and fertilization, used to describe female sperm storage.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

insectivore

An animal that eats mainly insects or spiders.

internal fertilization

fertilization takes place within the female's body

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

nocturnal

active during the night

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

venomous

an animal which has an organ capable of injecting a poisonous substance into a wound (for example, scorpions, jellyfish, and rattlesnakes).

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

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Myers Enterprises II 2009 - 2012. 2011. "Scytodes thoracica (Spitting spider)" (On-line). Global Species. Accessed January 26, 2012 at http://globalspecies.org/ntaxa/65738.

Laguna College. Spider Fauna in Philippine citrus and their note as predator in the control of insect. PCARRD-ASSP Proj. No. 89-38623. Taguig, Philippines: The Science and Technology Information of the Philippines. 1989. Accessed January 17, 2013 at http://scinet.dost.gov.ph/union/ShowSearchResult.php?s=2&f=&p=&x=&page=&sid=1&id=Spider+fauna+in+Philippine+citrus+and+their+note+as+predator+in+the+control+of+insect+pests.&Mtype=REPORTS.

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