How to Identify a Barn Spider: A Comprehensive Guide
Barn spiders, scientifically known as *Araneus cavaticus*, are common arachnids found throughout North America. Often mistaken for other orb-weaver spiders, identifying a barn spider accurately is crucial for understanding the local ecosystem and addressing any potential concerns about their presence. While generally harmless, recognizing these spiders can ease anxieties and provide valuable insights into their behavior and habitat. This comprehensive guide provides detailed steps and instructions to help you confidently identify a barn spider.
## Understanding Barn Spiders
Before diving into the identification process, it’s essential to understand the general characteristics of barn spiders. They are orb-weavers, meaning they construct large, circular webs to capture their prey. These webs are typically found in sheltered locations, such as barns, sheds, under eaves, and other similar structures, hence their name. Barn spiders are nocturnal hunters, actively repairing and rebuilding their webs at night. During the day, they typically retreat to a secluded spot near their web, often under a leaf, in a crack, or within the structure they inhabit.
## Step-by-Step Identification Guide
Follow these detailed steps to accurately identify a barn spider:
**1. Observe the Size and Shape:**
* **Size:** Barn spiders are relatively large spiders. Adult females typically range from 0.5 to 1 inch (13-25 mm) in body length, while males are slightly smaller, usually measuring between 0.3 to 0.7 inches (8-18 mm). Note that size can vary depending on the spider’s age and the availability of food. Young barn spiders will, of course, be considerably smaller. Therefore, consider other characteristics in conjunction with size. Measuring the spider, if possible, provides valuable data for comparison. You can use a ruler or tape measure, being careful not to disturb or harm the spider.
* **Shape:** Barn spiders have a classic orb-weaver body shape. Their abdomen is large and rounded, resembling an oval or teardrop. The cephalothorax (the combined head and thorax) is smaller and more compact. This distinct body shape helps differentiate them from spiders with more elongated or flattened bodies.
**2. Examine the Color and Markings:**
* **Color:** Barn spiders exhibit a range of colors, typically in shades of brown, tan, gray, or reddish-brown. The base color often varies depending on the individual spider and its environment. Pay attention to the overall color tone and any subtle variations.
* **Markings:** The most distinctive feature of barn spiders is the presence of prominent markings on their abdomen. These markings usually consist of a series of dark, wavy lines or blotches that run horizontally across the abdomen. The pattern can vary, with some spiders having more distinct and contrasting markings than others. Some individuals might have a single, darker stripe running lengthwise down the center of their abdomen, while others exhibit a more mottled or speckled appearance. Look closely at the pattern and arrangement of these markings, as they are key indicators for identification. Consider using a magnifying glass or taking a close-up photograph to better observe the details of the markings.
**3. Inspect the Legs:**
* **Length and Spination:** Barn spiders have relatively long and slender legs, typical of orb-weaver spiders. These legs are covered in fine hairs and spines, which aid in sensing vibrations and capturing prey. The spination (arrangement of spines) on the legs can be a subtle but useful characteristic for identification. Use a magnifying glass to examine the spines more closely. Note the density and pattern of the spines on each leg segment.
* **Color:** The legs of barn spiders are generally the same color as the cephalothorax, often in shades of brown or tan. Some individuals might have darker bands or rings on their legs, adding to the overall camouflage. Observe the color patterns on the legs and compare them to the body color.
**4. Observe the Web:**
* **Web Structure:** Barn spiders are known for constructing large, circular orb webs. These webs are typically vertically oriented and can span several feet in diameter. The web consists of a complex network of sticky spiral threads attached to radial support lines. The central hub of the web is usually non-sticky, allowing the spider to move around without getting caught in its own trap.
* **Web Location:** Barn spiders prefer to build their webs in sheltered locations, such as barns, sheds, under eaves, garages, and other similar structures. They typically choose spots that offer protection from wind and rain, as well as a stable anchor point for their web. Observing the location of the web can provide clues about the spider’s identity. While other orb-weavers might also build webs in similar locations, barn spiders are particularly common in these types of structures.
**5. Examine the Eye Arrangement (If Possible):**
* **Eye Pattern:** Spiders have eight eyes arranged in different patterns depending on the species. While examining the eye arrangement of a barn spider can be challenging without specialized equipment, it can provide a definitive identification. Orb-weaver spiders, including barn spiders, typically have two rows of four eyes each. The exact arrangement and spacing of the eyes can vary slightly, but this general pattern is consistent within the family. This step requires getting very close to the spider, which might not be feasible or safe in all situations. If you can safely observe the eye arrangement, it can provide valuable confirmation of the spider’s identity.
**6. Observe the Spider’s Behavior:**
* **Nocturnal Activity:** Barn spiders are primarily nocturnal hunters, meaning they are most active at night. They typically spend the day hidden near their web, emerging at dusk to repair or rebuild their web and wait for prey. Observing the spider’s activity patterns can provide clues about its identity. If you consistently see a large orb-weaver spider active at night in a barn or shed, it is likely a barn spider.
* **Web Repair:** Barn spiders are meticulous web builders and maintainers. They regularly repair their webs, replacing damaged or broken strands. They also rebuild their webs entirely, usually at night, to ensure they are in optimal condition for capturing prey. This dedication to web maintenance is a characteristic behavior of barn spiders.
* **Prey Capture:** When prey gets caught in the web, the barn spider quickly rushes to the victim, immobilizes it with silk, and injects venom. The spider then wraps the prey in silk for later consumption. Observing the spider’s prey capture behavior can provide insights into its hunting strategies.
**7. Consider the Habitat:**
* **Geographic Location:** Barn spiders are found throughout North America. Knowing the geographic location of the spider can help narrow down the possibilities. If you are in an area where barn spiders are known to occur, the likelihood of encountering one is higher.
* **Preferred Habitats:** As their name suggests, barn spiders are commonly found in barns, sheds, garages, and other outbuildings. They prefer sheltered locations that offer protection from the elements and a stable anchor point for their webs. If you find a large orb-weaver spider in one of these preferred habitats, it is more likely to be a barn spider.
## Differentiating Barn Spiders from Similar Species
Several other orb-weaver spiders can be mistaken for barn spiders. Here’s how to differentiate them:
* **Garden Spiders (Argiope species):** Garden spiders are also large orb-weavers, but they typically have more vibrant colors and distinct markings. Many garden spiders have bright yellow and black stripes on their abdomen, which are absent in barn spiders. Additionally, garden spiders often build webs in gardens and open fields, while barn spiders prefer sheltered locations.
* **Cross Orb-Weavers (Araneus diadematus):** Cross orb-weavers are similar in size and shape to barn spiders, but they have a distinctive cross-shaped marking on their abdomen. This marking is formed by a series of white spots that create a cross pattern. Barn spiders lack this distinct marking.
* **Shamrock Orb-Weavers (Araneus trifolium):** Shamrock orb-weavers can vary in color, but they often have a shamrock-shaped marking on their abdomen. This marking can be faint or prominent, depending on the individual spider. Barn spiders do not have a shamrock-shaped marking.
* **Hentz Orb-Weavers (Neoscona crucifera):** Hentz orb-weavers are smaller than barn spiders and have a more elongated abdomen. They also have different markings, typically consisting of a series of dark spots or lines arranged in a different pattern. They are often found in wooded areas rather than buildings.
## Addressing Concerns about Barn Spiders
While barn spiders can appear intimidating due to their size, they are generally harmless to humans. They are not aggressive and will only bite if they feel threatened. Their venom is not considered medically significant, and bites are rare. In most cases, a barn spider bite will result in mild pain and localized swelling, similar to a bee sting. You can treat the bite with over-the-counter pain relievers and antihistamines.
If you are concerned about the presence of barn spiders in your home or outbuildings, you can take several steps to discourage them:
* **Reduce clutter:** Remove clutter and debris from your property to eliminate potential hiding places for spiders.
* **Seal cracks and crevices:** Seal any cracks or crevices in your foundation, walls, and windows to prevent spiders from entering your home.
* **Install screens:** Install screens on windows and doors to keep spiders out.
* **Use natural repellents:** Use natural spider repellents, such as peppermint oil or vinegar, to deter spiders from entering your home.
* **Relocate spiders:** If you find a barn spider in an undesirable location, you can gently relocate it to a more suitable habitat. Use a container or jar to capture the spider and release it in a nearby wooded area or garden.
## Conclusion
Identifying a barn spider requires careful observation of its size, shape, color, markings, web structure, and behavior. By following the steps outlined in this guide, you can confidently distinguish barn spiders from other similar species. Remember that barn spiders are generally harmless and play an important role in the ecosystem by controlling insect populations. While it’s natural to be wary of spiders, understanding their characteristics and behavior can help you appreciate these fascinating creatures. If you have persistent concerns about spiders, consult with a pest control professional for advice and assistance.
By taking the time to learn about barn spiders and other local arachnids, you can develop a greater appreciation for the biodiversity around you and address any concerns in a safe and responsible manner. This knowledge empowers you to coexist peacefully with these fascinating creatures and maintain a healthy balance in your environment.