Scotophaeus blackwalli (Mouse Spider)

About Scotophaeus blackwalli

Taxonomic Hierarchy

→ Kingdom: Animalia
→ Phylum: Arthropoda
→ Class: Arachnida
→ Order: Araneae
→ Family: Gnaphosidae
→ Genus: Scotophaeus
→ Species: Scotophaeus blackwalli

Other Common Names

Mouse Spider, Stealthy Ground Spider, Ground Spider

Author

Author of species name: Tamerlan Thorell. First year published: 1871, as Drassus blackwallii.

Pronunciation

skoh-toh-FEE-us black-WALL-eye

Meaning

The genus name Scotophaeus is latinized Greek for “dark gray” (Cameron 2005). The specific epithet, blackwalli, is in recognition of the British naturalist, John Blackwall.

Notable Previous Names

Herpyllus blackwalli

Identifying Traits of Scotophaeus blackwalli

Size

Body length (excluding legs) of adult female ranges from 9-12 mm; adult males range from 6-9 mm.

Female Primary Colors

Male Primary Colors

Eye diagram of Scotophaeus blackwalli

Eyes

Total of eight eyes in two rows of four. When viewed from the front, both rows are very slightly procurved (curved upwards). The anterior median eyes (middle pair in the bottom row) are the largest pair, while the posterior median eyes are the smallest. In spiders, the anterior median eyes are considered the primary eyes, while the others are considered “secondary.” Viewed from some angles, the secondary eyes can appear white or silver because of a light-reflecting, crystalline structure inside them called a “tapetum.”

Legs

These spiders seem to be built for speed and, with the help of dense brushes of hairs (scopulae & claw tufts) on the last two segments of their legs, they can easily maneuver walls and ceilings with ease. In relation to body size, their legs are not very long, but are strong and thick, especially in the adult females. All legs are noticeably velvety or hairy-looking, more so in adult specimens, and are a solid brownish-orange color. Unlike web-building spiders, which usually have three tiny claws on the very tip of each leg, this hunting species only has two claws.

Body

Both genders are very similar-looking. The body of this species is somewhat slender and flattened, with the cephalothorax and abdomen essentially equal in size. The carapace is the same color as the legs, brownish-orange, and is covered in reflective silvery hairs. The elongated abdomen is dark gray and appears velvety and soft, reminiscent of a mouse. Even from a distance, one can see how furry the spider looks. The long, cylindrical “tail-pipe” spinnerets help to peg it as a member of the family Gnaphosidae.

Range of Scotophaeus blackwalli

Scotophaeus blackwalli can be found in the following states, provinces and territories across the United States and Canada. Our current understanding of each spider's distribution is drawn from numerous scientific publications and online spider submissions, in order to be as accurate as possible. It is important to remember that spiders do not adhere to the territorial lines decided on by humans, therefore these ranges are subject to change.

Important Range Notes

This is a cosmopolitan species that sometimes gets inadvertently transported to new locations via commerce and other human activity. It was probably transferred to North America from Europe. So far it is found along the Pacific Coast south into Mexico, along the coast of the Gulf States, and a few scattered records from elsewhere (including Colorado and Hawaii). It is also found in Europe, of course, as well as some countries in South America.

United States

Canada

Additional Information

Habitat

In North America, this species is almost always collected in and around buildings, but has also been found under tree bark or in shrubs. The all-encompassing common name for the entire family Gnaphosidae is “Stealthy Ground Spiders,” but it is not entirely accurate since many of the species, Scotophaeus blackwalli included, are found on trees and walls, high off the ground.

Web

This is a nocturnal hunting spider that does not spin a web to catch prey; it hunts “on foot” instead. It uses its silk for other purposes, such as safety lines, egg sacs, and little silken daytime retreats. Incidentally, we have noted in our observations that the “chamber” of webbing created around the egg sac is actually a pretty extensive labyrinth of silk (see example).

Season

Females can be found as adults at any time of year, but summer and fall are typically when the males reach maturity.

Food

Prey is any insect or other spider it is able to chase down and subdue. Scotophaeus blackwalli is very fast and can climb walls and ceilings with ease, which makes it quite a skilled and agile predator. They are basically free “pest control” inside the home. In addition, as has been observed with various other species, the “Mouse Spider” sometimes feeds (or scavenges, rather) on already dead insects. The British naturalist and arachnologist, W. S. Bristowe, remarked that he knew of several cases where lepidopterists had caught the spiders eating their pinned specimens during the night (Bristowe 1958).

Lifecycle

Egg laying typically takes place in the late summer or fall. The female chooses a safe, dark place to deposit her eggs and builds a silken “chamber” around herself. Within the chamber, she attaches a thin disc of silk to a flat surface. She then deposits her eggs onto the center of it and finishes off by covering them all with a thicker layer of silk about 10-12 millimeters in diameter. The eggs underneath create slight bulges in the center of the “disc.” She lays anywhere from 50-130 individual pale-colored eggs at a time. Spiderlings emerge from the egg shells in about 3-4 weeks, but stay inside the safety of the silken egg sac until they have completed their first molt. After that, they disperse and go their own individual ways.

Remarks

It is important to note that there are dangerously venomous mygalomorph spiders in the genus Missulena, family Actinopodidae, that are also nicknamed “Mouse Spiders.” They are found in Australia (and one species in Chile) and, aside from also being spiders, have nothing in common with the relatively innocuous Scotophaeus blackwalli.

Pictures of Scotophaeus blackwalli

General

Female Spiders

Male Spiders

Filtering options are grayed out when we do not have pictures for the given perspective. If you are a spider photographer, you can submit pictures of spiders to help fill any voids in our ever expanding library.
  • Scotophaeus blackwalli
  • Sex: FemaleFemale
  • Maturity: Adult
  • Attributes: Dorsal
  • City/Region: Windsor
  • Country: England
  • Scotophaeus blackwalli
  • Sex: FemaleFemale
  • Maturity: Adult
  • Attributes: Dorsal
  • City/Region: Windsor
  • Country: England
  • Scotophaeus blackwalli
  • Maturity: Immature
  • Attributes: Eyes
  • City/Region: Lakewood
  • State: Colorado
  • Country: United States
  • Scotophaeus blackwalli
  • Sex: FemaleFemale
  • Maturity: Adult
  • Attributes: Dorsal
  • City/Region: Lakewood
  • State: Colorado
  • Country: United States
  • Scotophaeus blackwalli
  • Sex: FemaleFemale
  • Maturity: Adult
  • Attributes: Eyes
  • City/Region: Lakewood
  • State: Colorado
  • Country: United States
  • Scotophaeus blackwalli
  • Sex: FemaleFemale
  • Maturity: Adult
  • Attributes: Dorsal
  • City/Region: Lincolnshire
  • Country: England
  • Scotophaeus blackwalli
  • Sex: FemaleFemale
  • Maturity: Immature
  • Attributes: Dorsal
  • City/Region: Krain
  • State: Washington
  • Country: United States
  • Scotophaeus blackwalli
  • Sex: FemaleFemale
  • Maturity: Immature
  • Attributes: Dorsal, Lateral
  • City/Region: Krain
  • State: Washington
  • Country: United States
  • Scotophaeus blackwalli
  • Sex: FemaleFemale
  • Maturity: Adult
  • Attributes: Gravid, Lateral
  • City/Region: Edinburgh
  • Country: Scotland
  • Scotophaeus blackwalli
  • Maturity: Immature
  • Attributes: Spiderlings
  • City/Region: Krain
  • State: Washington
  • Country: United States
  • Scotophaeus blackwalli
  • Sex: FemaleFemale
  • Maturity: Adult
  • Attributes: Egg Sacs, Webs
  • City/Region: Krain
  • State: Washington
  • Country: United States
  • Scotophaeus blackwalli
  • Maturity: Immature
  • Attributes: Egg Sacs, Spiderlings
  • City/Region: Krain
  • State: Washington
  • Country: United States
  • Scotophaeus blackwalli
  • Sex: FemaleFemale
  • Maturity: Adult
  • Attributes: Lateral
  • City/Region: Krain
  • State: Washington
  • Country: United States
  • Scotophaeus blackwalli
  • Sex: FemaleFemale
  • Maturity: Adult
  • Attributes: Dorsal, Gravid
  • City/Region: Krain
  • State: Washington
  • Country: United States
  • Scotophaeus blackwalli
  • Maturity: Immature
  • Attributes: Lateral, Spiderlings
  • City/Region: Krain
  • State: Washington
  • Country: United States
  • Scotophaeus blackwalli
  • Maturity: Immature
  • Attributes: Dorsal, Spiderlings
  • City/Region: Krain
  • State: Washington
  • Country: United States
  • Scotophaeus blackwalli
  • Sex: MaleMale
  • Maturity: Adult
  • Attributes: Eyes
  • City/Region: Krain
  • State: Washington
  • Country: United States
  • Scotophaeus blackwalli
  • Sex: MaleMale
  • Maturity: Adult
  • Attributes: Ventral
  • City/Region: Krain
  • State: Washington
  • Country: United States
  • Scotophaeus blackwalli
  • Sex: FemaleFemale
  • Maturity: Adult
  • Attributes: Dorsal
  • City/Region: Krain
  • State: Washington
  • Country: United States
  • Scotophaeus blackwalli
  • Sex: MaleMale
  • Maturity: Adult
  • Attributes: Dorsal, Lateral
  • City/Region: Krain
  • State: Washington
  • Country: United States

References and Further Reading

Various Research Papers

Scientific Diagrams and Keys for Identification

References for the Casual Reader

 

Species guide last updated: March 11, 2014

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