The Sicarius terrosus spider is a member of the family Sicariidae. Originating in Chile, this species is now also known as Sicarius thomisoides, but it is still more often referenced by its original name. Using an illustration by Hercule Nicolet, biologist Charles A. Walckenaer published a description of this species in 1847.
Habitat of Sicarius Terrosus
The Arica y Parinacota, Atacama, Coquimbo, O’Higgins, Santiago Metropolitan, Tarapacá, and Valparaiso areas of Chile are all home to the Neotropical species Sicarius terrosus.
Sicarius terrosus is found in a variety of dry environments throughout the Chilean coast, from sandy beaches and rocky cliffs to inland deserts. Arthropods like centipedes and spiders like the ground spider, Solifugae, which is known as the sun spider or camel spider, and the recluse spider (Loxosceles) fall prey to Sicarius terrosus. This spider voluntarily takes refuge behind huge stones, where it leaves egg cocoons on their surface.
There is one record of this species in the Buenos Aires province of Argentina, but it has probably been mislabeled. But this species is more likely to occasionally appear in southern Peru.
Morphology of Sicarius Terrosus
Size
The body length of Sicarius terrosus ranges from 12 to 20 mm. The opisthosoma (rear part of the body) of males is 6.7 mm long and 5.4 mm wide, while their carapax (front part of the body) is between 4.7 and 7.7 mm in length.
The carapax length ranges from around 5.6 to 8.17 mm in female Sicarius terrosus, with one specimen measuring around 6.25 mm in width along the opisthosoma.
Coloring
On Sicarius terrosus spiders, the sternum and legs are orange, and opisthosomas are brownish gray; the chelicerae (‘jaws’), labium (a mouthpart), and endites (leg lobs) are reddish brown; and the carapax is a pale reddish brown.
There are no ocular tubercles (the raised areas where the eyes are situated) on the carapax at all in the head area of Sicarius terrosus, making the cephalic region much thinner than in S. yurensis.
Body Features
A single row of macroscopic setae (hair-like structures) surrounds the carapax. Like S. yurensis, the sternum of this species is shaped like an oval, but unlike other representatives of the genus, it is more elongated than it is broad.
Both sexes of Sicarius terrosus have between five and six thorns on their thighs. The anterior-lateral region of the male’s thighs does not include any black setae (bristles). The palps (second pair of appendages, or pedipalp) on the legs of the male are slightly bent and transition smoothly into an embolus (breeding organ).
In contrast to male reproductive organs, female reproductive tissues of Sicarius terrosus (or Sicarius thomisoides) lack spherical reservoirs and instead have spermathecae with 8–20 branches. Female immature stages are characterized by pre-spermatheca that contain just a few short, finger-shaped branches.
Venom
All recluse spiders, including Sicarius terrosus, generate venom that includes the sphingomyelinase D enzyme, making it dermonecrotic. It is unusual, being present only in a few dangerous bacteria.
Venom from Sicarius terrosus is so potent that it can produce open sores up to an inch in diameter, destroy tissue, and reduce blood and blood vessel thickness. Experimentally, rabbits attacked by these spiders perished within hours, but there isn’t much information available concerning the effects of the venom on people.
Keeping Sicarius Terrosus as a Pet
Desert-themed terrariums are ideal for Sicarius terrosus. A tank with a base size of 8 by 8 inches (20 by 20 cm) and a height of 40 inches (15 cm) is suitable for an adult specimen. The substrate has to be loose and dry; rinsed and roasted sand is an excellent choice.
Expect daytime highs of 85 degrees Fahrenheit (30°C) and lows of 70 degrees Fahrenheit (22°C) inside the tank. Because of the need for low humidity (between 30 and 40 percent), watering should be kept to a minimum. Although the spider isn’t hostile and won’t try to scale glass, only experienced breeders should keep it due to its speed and toxicity, which can damage mammal organs.
Taxonomy
Using an illustration by Hercule Nicolet, biologist Charles A. Walckenaer published a description of this species in 1847. This same species was also named by Nicolet as Thomisoides minorata, Thomisoides terrosa, and Thomisoides rubripes two years later, in 1849.
Ivan Magalhaes, Antonio Brescovit, and Adalberto Santos were the first to classify these names as synonyms of S. thomisoides in 2017. Formerly known as Thomisoides terrosus and Sicarius terrosus, Sicarius levii was also officially characterized in 2017 by the aforementioned three authors.
In addition, Sicarius yurensis, which had been considered a subspecies of S. terrosus, was upgraded to the status of a whole species by these authors.
Variability in the structure of the male and female copulatory apparatus and reproductive organs within S. thomisoides suggests that it may be a complex of twin species.