Which of the following pests have a violin shape on the back of the neck?

The brown recluse spider is known for its distinctive violin shape marking on the dorsal side of its cephalothorax, which can resemble a violin or fiddle. This feature is a key characteristic that helps in identifying this particular species among other spiders. The violin shape typically has a darker color than the surrounding body, making it more prominent.

In contrast, the other spider options do not share this specific marking. The wolf spider, while a common spider, lacks any distinctive violin shape; it has a more robust and stocky appearance. The black widow spider is recognized for its glossy black body and the red hourglass marking on its abdomen, rather than any markings on its neck. The orb weaver spider primarily has a rounded, bulbous abdomen with various color patterns, but it does not showcase any violin-shaped markings either.

Thus, the brown recluse spider is singular in possessing this notable feature, making it the correct answer to the question about which pests display the violin shape on their bodies.