Spiders do not possess chewing jaws or teeth, making their mouth structure fundamentally different from mammals or insects. Located on the cephalothorax, the feeding apparatus is a highly specialized collection of modified limbs and openings. These tools are designed entirely for piercing, subduing, and ingesting liquid food, reflecting an evolutionary path focused on liquefying prey.
The Defining Features: Chelicerae and Fangs
The most visible components of a spider’s feeding apparatus are the chelicerae, a pair of strong appendages located directly in front of the mouth opening. These structures are often compared to jaws, but their function is primarily for grasping, injecting, and holding prey. Each chelicera consists of a large basal segment and a movable, pointed fang at the tip.
The fang is a sharp, needle-like structure that serves as the hypodermic injector for venom in nearly all species. Venom glands are located within the basal segment of the chelicerae or extend into the cephalothorax, delivering the venom through a tiny opening near the fang’s tip. The chelicerae hold the subdued prey steady, creating the necessary punctures for venom delivery and the subsequent digestive process.
The orientation of the fangs divides spiders into two major infraorders. Mygalomorphs, such as tarantulas, have orthognathous chelicerae where the fangs move parallel to the body axis. Araneomorphs, or “true spiders,” possess labidognathous chelicerae, meaning their fangs move in a pincer-like motion, opposing one another at right angles to the body.
The Role of Pedipalps
Flanking the chelicerae are the pedipalps, a second pair of appendages often mistaken for a fifth pair of legs. These jointed structures are integral to the feeding process, acting as sophisticated tools for handling and sensing. Pedipalps are highly sensitive and explore the prey item, providing chemical feedback about its suitability as a meal.
Once prey is secured, the pedipalps rotate and manipulate the food, holding it in place during venom injection and the later stages of digestion. The basal segments, known as maxillae or endites, are often armed with serrated edges or dense hairs. These structures help crush and mash the prey, working digestive fluids into the tissues.
In male spiders, the pedipalps have an additional, highly modified role. They feature an enlarged tip used exclusively for the transfer of sperm during mating.
The Feeding Mechanism: External Digestion and Sucking
Spiders cannot physically chew and swallow solid food because their digestive tract is extremely narrow and only capable of handling liquids. External digestion begins when the spider regurgitates a cocktail of powerful digestive enzymes onto or into the captured prey. These enzymes, which include proteases and lipases, begin breaking down the prey’s internal tissues, effectively liquefying the meal outside the spider’s body.
The true mouth opening is a tiny slit located behind the chelicerae and between small mouthparts like the labium and the rostrum. This opening leads directly into the pharynx, which connects to a highly muscular structure called the sucking stomach. This specialized organ is the primary pump for ingestion, using powerful muscles to rapidly expand its volume and create a strong vacuum.
The vacuum action draws the liquefied contents of the prey into the spider’s foregut. For larger or tougher prey, the spider engages in a periodic reflux process, repeatedly pumping the liquid back out onto the meal and sucking it back in. This ensures maximum saturation and digestion efficiency, ultimately leaving behind only a small, indigestible pellet of exoskeleton and other hard parts.