Identifying a spider based solely on a white dot on its back is challenging because many species share similar coloration patterns. This feature, however, strongly points toward a specific group of active hunters found across North America. To confirm identification, the spot’s exact shape, the spider’s overall structure, and its behavior are necessary. The most frequent candidate matching this description is a member of the jumping spider family, known for its distinctive appearance and daytime activity.
The Primary Identification: Bold Jumping Spiders
The spider most commonly described as black with a white dot is the Bold Jumping Spider (Phidippus audax). This species is a compact, hairy spider with a black body, ranging from 6 to 15 millimeters in length. The identifying white spot is located on the abdomen, but mature specimens frequently display three spots: a central triangular spot and two smaller, circular spots positioned lower down. These markings are not always white; juveniles often display bright orange or yellowish spots. A striking feature of the Bold Jumper is its iridescent chelicerae (jaws), which shimmer with metallic green or blue colors, and its large, prominent anterior median eyes give it excellent vision.
Other Spiders With Light Markings
While the Bold Jumper is the most likely match, several other spiders possess light-colored markings on their dorsum (back) that fit a casual description.
- Crab Spiders (family Thomisidae), such as the Goldenrod Crab Spider, are ambush predators often found on flowers. While usually white or yellow for camouflage, some species have distinct white patterns on a darker background. They are recognized by their crab-like appearance, holding their front legs out to the sides.
- Juvenile or male Black Widow spiders (Latrodectus species) may display white, yellow, or red spots on the top of their abdomen, unlike the female’s classic red hourglass on the underside.
- The Spiny-backed Orb Weaver (Gasteracantha cancriformis) features a hard, spiny abdomen that is often black with white spots, though its shape is unmistakable.
- The Parson Spider (Herpyllus ecclesiasticus) has a dark body with a distinct white or light-gray band running longitudinally down the center of its gray abdomen.
Identifying Clues Beyond the Dot
A spider’s behavior and habitat provide the most practical clues to identification beyond physical markings. The Bold Jumping Spider is a diurnal hunter, meaning it is active during the day and relies on its exceptional eyesight to stalk and pounce on prey. Unlike many common spiders, it does not build webs to capture food, although it spins a silken dragline as a safety tether during its jumps. Observing a small, black spider actively moving in a jerky, irregular gait on a sunlit surface suggests a jumping spider. Other spiders that might have a white dot are often sedentary web-builders or nocturnal hunters. Orb weavers construct large, circular webs, relying on vibrations to detect prey. The Parson Spider is a swift, nocturnal hunter that spends its days hidden in silken retreats.
Assessing the Bite Risk
The Bold Jumping Spider is not considered medically significant to humans, and its venom is primarily effective against the small insects it hunts. Bites from this species are rare, typically occurring only if the spider is accidentally crushed or mishandled. They are far more likely to run away or assume a defensive posture than to bite. If a bite does occur, the symptoms are usually mild and comparable to a mosquito bite or bee sting, involving slight swelling, redness, and itching. These symptoms typically resolve within a day or two with simple care, such as cleaning the area and applying a cold compress. Medical attention is not required unless the symptoms worsen significantly or persist for more than 24 hours. Seek immediate medical care only if signs of a severe allergic reaction, such as difficulty breathing or severe swelling, develop.