Red-backed Jumping Spider
Phidippus johnsoni
Salticidae (Jumping Spiders), Order Araneae. Key family characteristics include large, forward-facing anterior median eyes providing exceptional stereoscopic vision, and a compact body adapted for active leaping rather than web-building.
Physical Description
Compact, robust body with a distinctively high, rounded cephalothorax and an oval-to-elongated abdomen. The body features a somewhat velvety texture due to dense, short hairs, with females showing pronounced sexual dimorphism in overall body size compared to males.
Size Estimate
Body length ranges from approximately 10 to 15 millimeters for females and slightly smaller for males, with a stout leg span proportional to a medium-to-large sized jumping spider.
Coloration & Markings
Striking coloration featuring a bright red or orange dorsal abdomen, frequently split by a distinct black longitudinal stripe down the center. The cephalothorax is predominantly black, sometimes accented with white hairs, and the legs are black with occasional white banding.
Web Type
Does not build a traditional web to catch prey. Instead, constructs a silken retreat or relay sac under bark, rocks, or within crevices, used for molting, sleeping, and egg-laying.
Eye Arrangement
Typical salticid pattern consisting of eight eyes arranged in three rows. The anterior median eyes are exceptionally large and provide high-resolution, color vision, flanked by smaller anterior lateral eyes, with two additional rows on top of the carapace.
Leg Characteristics
Robust and powerful legs, relatively short compared to orb-weavers, with the first and second pairs often slightly stouter and used for subduing prey and signaling during courtship. Equipped with dense scopulae and claw tufts for clinging to vertical and smooth surfaces.
Venom & Safety Information
Venom Information
Contains neurotoxic venom used primarily to immobilize small invertebrate prey. The venom is not specialized for vertebrate defense and poses minimal risk to humans.
Medical Significance
Harmless to humans. Bites are extremely rare and typically only occur if the spider is directly squeezed or trapped against the skin. Symptoms are generally limited to minor localized pain, redness, and swelling, similar to a mosquito bite.
Safety Recommendations
No special precautions needed as they are beneficial and non-aggressive. If removal from a home is desired, gently guide the spider into a small container using a piece of card and release it outdoors.
Habitat & Behavior
Habitat & Range
Found primarily in western North America, ranging from British Columbia down through California and into parts of the Rocky Mountains. Prefers open areas, grasslands, chaparral, and the sunny exterior walls of buildings.
Behavior & Temperament
Active diurnal hunter relying on acute eyesight to stalk and pounce on prey. Generally docile and curious toward humans, though mature females guarding egg sacs may display defensive posturing if cornered.
Diet & Prey
Carnivorous generalist feeding on a wide variety of small insects including flies, mosquitoes, aphids, and other spiders, capturing them through a calculated stalking and leaping ambush technique.
Seasonal Activity
Most active during spring and summer months when warm weather provides abundant prey and optimal conditions for foraging and mating. Overwinters inside silken retreats hidden beneath bark or structural siding.
Description
The Red-backed Jumping Spider is one of the most charismatic and visually striking arachnids in North America. With its brilliant red dorsal abdomen contrasting against a deep black velvet body, it easily catches the eye of nature enthusiasts. As an active hunter boasting exceptional vision, it navigates its environment with remarkable agility, frequently pausing to peer curiously at observers.
Key Features
Vibrant red or orange dorsal abdomen marked with a central black stripe, combined with a black cephalothorax and exceptionally large, forward-facing anterior median eyes typical of the Salticidae family.
Similar Species
Can be confused with other red-backed jumping spiders such as Phidippus cardinalis or certain color morphs of Phidippus apacheanus, distinguished primarily by range, subtle variations in the black abdominal stripe, and carapace markings.
Life Cycle
Females construct silken egg sacs in protected crevices containing around 100 to 200 eggs. Spiderlings emerge and disperse after their first few molts. They overwinter as juveniles or sub-adults, reaching maturity in the spring or summer.
Ecological Importance
Serves as an effective natural predator and biological control agent by regulating populations of nuisance insects, garden pests, and disease vectors around homes and natural habitats.
Conservation Status
Not evaluated by the IUCN, but populations are generally stable and widespread across their native geographic range, facing no significant conservation threats.
Interesting Facts
Jumping spiders can leap up to 50 times their own body length using a sudden hydraulic pressure change in their legs. They are also known to perceive colors across the UV spectrum and engage in complex, visual courtship dances.
Photography Tips
Best photographed in natural daylight using a macro lens from a low angle to capture their expressive eyes. Approach slowly to avoid startling them, and use a fast shutter speed to freeze movement.
Identified: 2026-08-17T17:34:26.711080