Arizona’s diverse ecosystems, from arid deserts to mountainous regions, support a wide array of spider species. These arachnids play a significant role in the local environment. Understanding the types of spiders present in Arizona, their behaviors, and habitats helps residents and visitors appreciate the natural diversity without unnecessary concern.
Common and Harmless Arizona Spiders
Arizona is home to numerous spider species that pose little to no threat to humans despite their often intimidating appearance. These spiders are beneficial, helping to control insect populations.
Orb weaver spiders are recognized for their intricate, circular webs, which can span up to six feet. They are often found in gardens and between shrubs, with many species brightly colored, featuring striped or spotted patterns on their distinctive abdomens. These spiders are non-aggressive, and their bites are not toxic to humans.
Wolf spiders are active hunters rather than web-builders. These large, hairy spiders, like the Carolina wolf spider, can reach over an inch in body length and are typically gray to dark brown with thicker legs. They are nocturnal, often found in gardens, open fields, or indoors. Their bites are rare and usually not a cause for concern.
Jumping spiders, characterized by compact bodies, stocky legs, and large, forward-facing eyes, are small but agile. Species like the Bold Jumping Spider, typically black with white spots, are active daytime hunters that leap to ambush prey. They are harmless and more likely to retreat if disturbed.
Spiders of Medical Concern in Arizona
While most Arizona spiders are harmless, a few species are considered medically significant due to their venom.
The Western Black Widow (Latrodectus hesperus) is identifiable by its glossy black body and a distinct red or orange hourglass marking on its abdomen. Female black widows, larger than males, typically measure about 1.5 inches including leg span. They prefer dark, secluded places like woodpiles, sheds, and crawl spaces, spinning irregular, strong webs. While their venom can cause muscle cramps, nausea, and difficulty breathing, severe outcomes are rare. Bites are usually defensive, occurring when the spider feels threatened, and medical attention is important if a bite is suspected.
Recluse spiders, belonging to the genus Loxosceles, are another group of medical concern. In Arizona, the Desert Recluse (Loxosceles deserta) and the Arizona Brown Spider (Loxosceles arizonica) are native. These spiders are light to yellowish-brown, measuring around 0.5 inches in body length with a leg span of 1 to 1.5 inches. They often have a violin-shaped marking on their cephalothorax, though this can be faint or absent in some Desert Recluse individuals.
Recluse spiders are reclusive, preferring dry, undisturbed areas such as woodpiles, storage boxes, or attics. Their bites can cause tissue damage, leading to a spreading sore, and medical evaluation is recommended if a bite occurs. The Brown Recluse (Loxosceles reclusa), often discussed in other regions, is not native or commonly established in Arizona.
General Spider Identification Tips
Identifying spiders involves observing several key physical characteristics.
All spiders possess two main body segments: a fused head and thorax (cephalothorax) and an abdomen. They consistently have eight legs, unlike insects which have six, and lack antennae or wings. Their size, including body length and leg span, provides initial clues.
Examining eye arrangement is another useful identification feature; while most spiders have eight eyes, their number, size, and pattern vary significantly between species. Web characteristics are also indicative; some spiders, like orb weavers, create intricate, symmetrical webs, while others, such as black widows, build messy, irregular ones. Many spiders, like wolf spiders, do not spin webs for hunting, relying instead on active pursuit. Observing these elements without direct handling is advised.
Distinguishing Look-Alike Spiders
Differentiating between harmless spiders and those of medical concern often requires attention to specific details, as color alone can be misleading.
Many brown spiders are commonly mistaken for recluse spiders. A key feature for recluse spiders is six eyes arranged in three pairs, a distinct characteristic setting them apart from most other spiders which have eight eyes. While many recluse spiders, including the Arizona Brown Spider, exhibit a violin-shaped marking on their cephalothorax, this mark can be subtle or absent in the Desert Recluse, making eye arrangement a more reliable indicator.
Distinguishing black widows from other dark-colored spiders involves looking for specific markings. The Western Black Widow female is characterized by a shiny black body and a prominent red or orange hourglass shape on her abdomen. Some other dark spiders may have red markings, but the distinct hourglass shape is a primary identifier for black widows. Black widow webs are typically irregular and tangled, differing from the more structured webs of many other species.