What is a defining characteristic of the brown recluse spider?

The defining characteristic of the brown recluse spider is the dark fiddle-shaped marking on its back. This distinctive marking, which is often yellow to brown in color, usually has a shape that resembles a violin or a fiddle, hence the name. This pattern helps in identifying the brown recluse among other spider species, which may have different markings or lack such distinctive features altogether. Recognizing this marking can be crucial, as the brown recluse is known for its venomous bite, and proper identification can aid in avoiding potentially harmful encounters.

The other options present characteristics that are not applicable to the brown recluse. For example, while many spiders do have eyes, the brown recluse specifically has six eyes, which contradicts the claim of having eight. Additionally, the spider is not bright red; its color ranges from light yellowish-tan to brown. Lastly, the brown recluse typically grows to about half an inch in body length, with leg spans making it appear larger, but it does not reach up to 2 inches as suggested. Thus, the presence of the fiddle-shaped marking is a key factor in identifying this spider.