Wolf Spider Vs. Brown Recluse Spider: Differences That Confuse Us

Traits of wolf spiders
Wolf spiders and brown recluse spiders are both commonly found in the U.S., and are often confused for each other.
Did You Know?
The brown recluse spider is about half as large as the wolf spider. The latter is about 1.5 inches long, whereas the brown recluse can only grow to about 0.75 inches.
Wolf spiders and brown recluse spiders are often confused for each other, due to their similar appearance. However, there are notable differences between the two. Differentiating between these two is important, since while the bite of a wolf spider is harmless to humans, brown recluses are venomous, and can cause tissue damage. As a matter of fact, wolf spiders are also venomous and their bites can sting, but don't cause any long-term damage.

Let's look at the comparison between the wolf spider and the brown recluse spider in detail.
Wolf Spider or Brown Recluse Spider?
Though it is easy to confuse these two unrelated spider species, there are several tests that you can use to identify them.
Brown recluse range
Range of the Brown Recluse Spider
Wolf spiders are found virtually all over the world, apart from the Arctic and Antarctic Circles. Brown recluse spiders, on the other hand, are only found in southeastern North America, as shown image.

So, if you live anywhere apart from the highlighted region (majorly Texas to Georgia and as north as Kentucky, and parts of Iowa, Nebraska, Illinois, Indiana), you don't have to worry about brown recluse spiders, though local and easily terminable infestations of the spider have been found.
The Violin on the Neck
Violin markings of brown recluse spider
Violin markings on the cephalothorax of brown recluse spiders
Brown recluse spiders have markings on their cephalothorax (arachnid equivalent of a torso) that superficially resemble violins. This has led to them being called 'fiddleback spiders' or 'violin spiders'. Though other species of spiders (particularly cellar spiders and pirate spiders) have similar markings, it is one of the many traits that can help identify a brown recluse spider, since it clearly differs from the other two types of spiders in superficial visual characteristics. As far as their comparison with wolf spiders goes, the latter don't have any such markings.
Wolf spiders eyes
Wolf spiders have 8 eyes in 3 rows
Recluses spider eyes
Recluses have 6 eyes in 3 pairs
Both brown recluse and wolf spiders have contrasting and peculiar arrangements of eyes, which can be used to identify them. Wolf spiders have three rows of eyes, with the middle two being the most prominent, and the bottom 4 being the least conspicuous (the top 2 eyes are slightly hidden behind tufts of hair in the adjoining image). Brown recluse spiders, on the other hand, are one of the few spiders that do not have 8 eyes; they have 6. The 6 eyes are arranged in three pairs, clearly visible at the rounded end of the 'violin'.
Wolf spiders have stocky legs with spines
Wolf spiders have stocky legs with spines
Recluses have slender legs with hair
Recluses have slender legs with hair
All spiders, being arthropods, have 8 legs. However, the individual design of their legs varies massively between species. In this case, wolf spiders have stockier legs with spines. In contrast, the brown recluse spider's legs are much more slender, and don't have spines. Instead, they are often covered in fine hair.
Wolf spiders have colored patches and lines
Wolf spiders have colored patches and lines
Uniformly colored abdomen on recluses
Uniformly colored abdomen on recluses
The color of various individuals of both types may vary, but there is one important identifying factor. The brown recluse spider always has a uniformly-colored abdomen, while the wolf spider's abdomen has patches and lines in different colors. If the spider has a two-tone color scheme on its abdomen, it can't be a brown recluse (though there is no guarantee that it is a wolf spider, either).
Armed with these tips, you should now have no trouble in distinguishing between these two confusing species of arachnids. Remember: Wolf spiders―the spiny-legged, multicolored, eight-eyed, non-violin-marked ones―are perfectly safe for humans, while brown recluse spiders―the hairy-legged, uniformly colored, six-eyed, violin-marked ones―can cause serious injuries, and should be kept at arm's length.