Running Crab Spider, Philodromid Crab Spider
Philodromus sp. (likely Philodromus dispar or Philodromus vulgaris)
Philodromidae (Running Crab Spiders), Order Araneae. Philodromids are characterized by second legs that are usually noticeably longer than the first, flattened body shapes, and rapid agility without spinning capture webs.
Physical Description
Small, flattened dorsoventrally with a teardrop-shaped to oval abdomen and a rounded cephalothorax. The body is light brown to greyish, smooth with fine setae, and features laterally extending legs that allow it to fit into tight crevices.
Size Estimate
Very small individual, approximately 3-5 mm in body length with a leg span of around 8-12 mm. Given the tiny size relative to the outdoor plastic surface structure, this specimen appears to be a juvenile or small adult male.
Coloration & Markings
Muted greyish-tan and brown hues. A darker cardiac mark/stripe is visible longitudinally along the dorsal center of the abdomen, accompanied by faint darker lateral mottling along the carapace and abdomen for camouflage against bark and weathered surfaces.
Web Type
No web for prey capture. They are active free-ranging hunters. Females only spin a small, flattened white silk pad/sac to protect egg clutches in secluded crevices.
Eye Arrangement
Eight small, dark eyes arranged in two strongly recurved rows of four across the front of the carapace, providing wide-angle detection of movement.
Leg Characteristics
Slender, radially arranged legs held sideways in a crab-like posture. The second pair of legs (Leg II) is visibly longer than the rest, enabling extremely quick sideways and forward running movements across surfaces.
Venom & Safety Information
Venom Information
Contains mild, insect-specific venom used to quickly immobilize small insect prey. The venom lacks medical importance and is harmless to humans.
Medical Significance
Non-dangerous / Harmless. Fangs are generally too small to pierce human skin, and bites are extremely rare, resulting at most in minor localized redness comparable to a tiny bug bite.
Safety Recommendations
No action needed as it poses zero threat to humans or pets. If found indoors, safely relocate outside using a small container and paper.
Habitat & Behavior
Habitat & Range
Widespread across North America, Europe, and Asia. Found on tree bark, foliage, outdoor wooden decks, fences, patio furniture, and exterior walls of structures.
Behavior & Temperament
Extremely fast, agile, and skittish. When disturbed, it darts away in quick bursts or flattens itself against surfaces to evade detection. Shy and completely non-aggressive toward humans.
Diet & Prey
Active ambush predator feeding on small flying or crawling invertebrates such as midges, aphids, gnats, leafhoppers, and small flies.
Seasonal Activity
Most active from mid-spring through autumn. Subadults overwinter under tree bark, leaf litter, or structure crevices.
Description
A nimble, small running crab spider resting on a white plastic surface outdoors. Recognized by its flattened light brown body, distinct dark central stripe on the abdomen, and crab-like lateral leg posture, this beneficial spider is a master of camouflage and swift hunting without the use of webs.
Key Features
Flattened body; second pair of legs visibly longer than others; brownish mottled pattern with a dark dorsal cardiac stripe; crab-like resting posture.
Similar Species
Thomisidae (Thomisid Crab Spiders, which have much larger/thicker legs I and II compared to III and IV), Lycosidae (Wolf Spiders, which have different eye arrangements and heavier bodies), and Salticidae (Jumping Spiders, which have larger anterior median eyes).
Life Cycle
Overwinters as a subadult under bark or in dry crevices. Reaches adulthood in spring or early summer, mates, and females lay eggs wrapped in small silk egg sacs, guarding them until hatching.
Ecological Importance
Serves as an efficient biological control agent for garden pests, preying on aphids, midges, and small flies around outdoor vegetation and home exteriors.
Conservation Status
Not evaluated (NE). Common and widespread across urban, suburban, and natural landscapes.
Interesting Facts
Unlike true crab spiders (Thomisidae), running crab spiders have leg pairs of more uniform length with leg II being the longest, making them exceptionally fast runners across smooth or uneven vertical surfaces.
Photography Tips
Use a macro lens or high magnification with good lighting to capture the fine dorsal pattern and eye layout. Keep the camera parallel to the surface it is resting on due to its small size.
Identified: 2026-07-27T21:12:35.236130