If you observed what appeared to be a spider with antennae, you likely saw something else entirely. True spiders do not possess antennae, a feature unique to insects and some other arthropods. This article will clarify what anatomical structures spiders actually have and introduce other creatures that are frequently mistaken for spiders, helping you accurately identify your next eight-legged encounter.
Understanding Spider Anatomy
Spiders, as arachnids, possess a pair of appendages called pedipalps, which are located near their mouthparts. These pedipalps are jointed and can resemble small legs, serving various functions such as sensing objects, manipulating food, and in male spiders, transferring sperm during reproduction. In adult male spiders, pedipalps are often noticeably enlarged or bulbous at the tips, aiding in their identification.
Beyond pedipalps, spiders typically have eight walking legs and a body divided into two main segments: the cephalothorax (a fused head and thorax) and the abdomen. The cephalothorax houses their simple eyes and their chelicerae, which are mouthparts equipped with fangs for injecting venom into prey. The abdomen contains vital organs, including digestive and reproductive systems, and spinnerets that produce silk for webs, egg sacs, and other uses.
Creatures Often Confused with Spiders
Many creatures are commonly mistaken for spiders, particularly those with long, slender appendages. A prime example is the harvestman, often called “daddy longlegs.” While arachnids like spiders, harvestmen lack silk-producing spinnerets. Their bodies appear as a single, fused oval segment, unlike the distinct two-part body of a true spider. Harvestmen do possess antennae-like structures; their second pair of legs is often elongated and used as sensory “feelers” to explore their environment.
Certain insects can also be confused with spiders if they possess long antennae. Spider beetles, for instance, have rounded bodies and long legs that can make them appear spider-like, but they only have six legs and distinct, long antennae. Other insects like crickets also have long antennae, which can lead to misidentification, although they clearly exhibit six legs and three distinct body segments (head, thorax, and abdomen). Even some amblypygids, or whip spiders, despite being arachnids with eight legs, have their anterior legs modified into extremely long, whip-like sensory appendages that function much like antennae.
Distinguishing Features
Differentiating between true spiders and other creatures often mistaken for them involves observing a few key anatomical features. Spiders consistently have eight legs, whereas insects, including those with long antennae like crickets or spider beetles, will only have six. The most obvious difference lies in their body segmentation: spiders have two distinct body parts—a cephalothorax and an abdomen connected by a narrow waist (pedicel)—while harvestmen have a single, fused, oval-shaped body. Insects, in contrast, feature three distinct body segments: head, thorax, and abdomen.
Another distinguishing characteristic is the presence or absence of antennae. True spiders do not have antennae; any long, thin appendages near their head are pedipalps. Harvestmen, however, use their elongated second pair of legs as sensory organs resembling antennae. The ability to produce silk and build webs is also exclusive to spiders, as harvestmen lack spinnerets. Finally, while spiders typically have six to eight simple eyes arranged in various patterns, harvestmen usually have only two eyes, positioned on a raised tubercle in the middle of their body.