Red-backed Jumping Spider, Johnson's Jumping Spider
Phidippus johnsoni
Salticidae (Jumping Spiders), Order Araneae. Key family characteristics include large forward-facing anterior median eyes providing exceptional stereoscopic vision, robust bodies, and specialized jumping ability.
Physical Description
Compact and robust body shape with a high, rounded cephalothorax and an oval-shaped abdomen. The body is densely covered in fine setae giving it a velvety texture. Noticeable sexual dimorphism exists, with females typically displaying a distinct bright red dorsal patch on the abdomen.
Size Estimate
Medium-sized jumping spider, approximately 10 to 14 millimeters in body length for females, with a leg span proportional to the sturdy body. This specimen appears to be a mature adult.
Coloration & Markings
Deep glossy black head and front legs contrasting sharply with a vibrant, velvety red dorsal abdomen. A faint black stripe is often visible running down the center of the red abdominal patch, while the underside and rear legs are predominantly dark.
Web Type
Does not build a traditional web for capturing prey. Instead, constructs a silken retreat (nest or sac) under bark, rocks, or in crevices, used for molting, sleeping, and egg-laying.
Eye Arrangement
Typical salticid arrangement consisting of eight eyes in three rows: two enormous anterior median eyes offering acute color vision, flanked by smaller anterior lateral eyes, with two rows of smaller eyes on top of the cephalothorax.
Leg Characteristics
Front legs are significantly thicker, longer, and more robust than the rear legs, covered in dark hairs, and adapted for leaping and subduing prey. The rear legs provide the explosive spring mechanism.
Venom & Safety Information
Venom Information
Contains neurotoxic venom used primarily to immobilize insect prey. The venom has very low potency relative to humans and is generally harmless unless an allergic reaction occurs.
Medical Significance
Not medically significant. Bites are rare and usually only occur when the spider is pressed directly against the skin. Symptoms are typically limited to mild localized pain, redness, and slight swelling, similar to a mosquito bite.
Safety Recommendations
No special precautions needed beyond avoiding handling them roughly. If found indoors, they can be gently guided into a container and released outside.
Habitat & Behavior
Habitat & Range
Found primarily in western North America, ranging from British Columbia down through California and into the Rocky Mountains. Prefers dry, open areas, chaparral, grasslands, and forest edges, often found on low vegetation, rocks, and wooden structures.
Behavior & Temperament
Active diurnal hunter relying on exceptional eyesight to stalk and pounce on prey. Generally docile and curious toward humans, though they can deliver a defensive bite if trapped or squeezed.
Diet & Prey
Carnivorous predator feeding on a wide variety of small insects, including flies, bugs, moths, and other spiders. Stalks prey like a cat before leaping with pinpoint accuracy.
Seasonal Activity
Most active during the warm spring and summer months. They seek sheltered crevices under bark or inside structures to overwinter during colder periods.
Description
The Red-backed Jumping Spider is a striking and charismatic arachnid easily recognized by its glossy black front end and vibrant red abdomen. As an active diurnal hunter, it navigates its environment with remarkable agility and curiosity, often turning to observe human onlookers with its large, expressive eyes. Safe, beneficial, and fascinating, it is a welcome resident in gardens and natural landscapes.
Key Features
Vibrant red dorsal patch on a black abdomen, glossy black cephalothorax and front legs, large forward-facing eyes, and characteristic bounding movement.
Similar Species
Can be confused with other red-backed jumping spiders such as Phidippus apacheanus or male Latrodectus (widow spiders), but differs by its stockier build, lack of an hourglass marking, and distinct jumping behavior.
Life Cycle
Females construct a silken retreat to lay a batch of eggs, guarding them diligently until they hatch. Spiderlings disperse via ballooning or crawling, undergoing multiple molts to reach maturity within a year.
Ecological Importance
Acts as a natural pest control agent by keeping populations of flies, mosquitoes, and garden pests in check while serving as prey for birds and lizards.
Conservation Status
Not threatened or endangered, maintaining robust and widespread populations throughout its native range.
Interesting Facts
Jumping spiders can leap up to 50 times their own body length using hydraulic pressure changes in their legs. They also possess color vision that includes the ultraviolet spectrum.
Photography Tips
Use a macro lens in bright natural light or with a diffuser. Approach slowly from the side or rear to avoid triggering their escape jump, and focus sharply on the large anterior eyes.
Identified: 2026-08-10T06:10:48.703672