Mouse Spider, European Mouse Spider
Scotophaeus blackwalli
Gnaphosidae (Ground Spiders), Order Araneae. Key family characteristics include cylindrical spinnerets and a flattened body for squeezing into crevices.
Physical Description
A medium-sized spider with a noticeably flattened cephalothorax and abdomen, allowing it to hide in narrow cracks. The abdomen is covered in fine, velvety hairs (setae) giving it a mammal-like texture, which is the source of its common name. The body is robust and aerodynamic for fast running.
Size Estimate
Estimated body length 8-12mm (females being larger). Total leg span approximately 20-30mm. This specimen appears to be an adult.
Coloration & Markings
Uniformly dark grey, charcoal, or brownish-black. There are no distinct patterns, stripes, or chevrons. The fine hairs on the abdomen often catch the light, giving it a subtle silvery or silky sheen.
Web Type
The Mouse Spider does not build a traditional capture web. Instead, it is a hunting spider that constructs a small, thick silk retreat (a tubular cell) in crevices or under rocks to rest in during the day.
Eye Arrangement
Typical of Gnaphosids: eight eyes in two rows of four. The eyes are relatively small, with the posterior median eyes often oval or irregular in shape rather than perfectly circular.
Leg Characteristics
The legs are strong, sturdy, and relatively medium in length compared to the body. They are covered in short hairs and lack prominent spines. The feet have specialized claw tufts that allow them to climb smooth surfaces like glass or walls with ease.
Venom & Safety Information
Venom Information
Possesses venom used to subdue insects. To humans, the venom is considered very low potency. It is not neurotoxic or necrotic in a medically significant way.
Medical Significance
Harmless to humans. A bite might cause minor localized redness, itching, or slight swelling, similar to a bee sting, but symptoms usually subside quickly. No special medical treatment is required unless an allergic reaction occurs.
Safety Recommendations
No specific safety precautions are needed as they are not dangerous. If you want to relocate one, use the cup-and-paper method to move it outside to a garden or woodpile.
Habitat & Behavior
Habitat & Range
Commonly found in North America and Europe. It is a synanthropic species, meaning it is often found in and around human dwellings. Preferred microhabitats include bark, leaf litter, wall crevices, and indoor areas like closets or under furniture.
Behavior & Temperament
An active nocturnal hunter. They are exceptionally fast runners that track down prey on foot rather than using a web. They are generally timid toward humans and will attempt to flee rapidly if disturbed. They are not aggressive.
Diet & Prey
Primarily feeds on other small insects and spiders. They use their speed to overwhelm prey and are known to be opportunistic, sometimes scavenging dead insects they encounter.
Seasonal Activity
Most active during the warmer months, though they are often seen year-round inside heated buildings. Mating typically occurs in summer and early autumn.
Description
Known as the Mouse Spider due to its grey, velvety appearance and rapid, scurrying movements, Scotophaeus blackwalli is a fascinating nocturnal ground hunter. Unlike orb-weavers, it relies on speed and agility to catch prey. While often found indoors, it is an excellent natural pest controller, quietly patrolling corners and crevices for unwanted insects.
Key Features
Velvety grey-black abdomen, cylindrical spinnerets at the rear, flattened body shape, and exceptionally fast scurrying movement.
Similar Species
Often confused with the 'Eastern Mouse Spider' (Zelotes) or other dark Ground Spiders. It is also sometimes mistaken for the Australian Mouse Spider (Missulena), which is a much more dangerous, heavily built mygalomorph not found in this context.
Life Cycle
Females produce a flat, disc-shaped egg sac inside their silk retreat. They exhibit some maternal care by guarding the sac until the spiderlings emerge. They typically live for 1 to 2 years.
Ecological Importance
Serves as an important predator of domestic pests like silverfish, flies, and small moths. They play a vital role in balancing insect populations in both urban and natural environments.
Conservation Status
Not evaluated by the IUCN, but considered common and widespread with stable populations throughout its range.
Interesting Facts
The 'Mouse Spider' name refers purely to its appearance and movement, not its size or aggression. They are remarkably adept at squeezing through gaps only a few millimeters wide because of their compressed body structure.
Photography Tips
Since they are fast and light-sensitive, use a fast shutter speed and try to capture the cylindrical spinnerets at the back of the abdomen for a positive identification. Macro shots of the abdominal 'fuzz' are particularly striking.
User Notes
I found it on the pavement
Identified: 2026-07-12T17:54:40.428305