Spiders possess a biology distinct from many other creatures, especially concerning their feeding apparatus. Unlike animals with conventional mouths and jaws for chewing, spiders employ highly specialized structures to consume their prey. These unique adaptations allow them to thrive in diverse environments. Understanding these structures provides insight into how spiders process food.
Chelicerae and Fangs
The most prominent components of a spider’s feeding system are its chelicerae. These paired appendages are located at the front of the spider’s cephalothorax, the fused head and thorax region. Each chelicera consists of a stout basal segment and a sharp fang at its tip. The fangs are hollow, serving as conduits for venom injected into prey.
Venom glands, which produce this neurotoxin, are situated within the basal segment of the chelicerae or extend further back into the cephalothorax. When a spider bites, it squeezes these glands to control the amount of venom delivered. This enables the spider to administer a dose appropriate for the prey or threat, or even a dry bite without venom. The fangs have chitin fibers arranged to provide rigidity, allowing them to penetrate the tough exoskeletons of insects.
Understanding Pedipalps
Positioned alongside the chelicerae, pedipalps are a pair of appendages. They serve distinct functions from the spider’s eight walking legs. Pedipalps are rich in sensitive chemical detectors, acting as organs for taste and smell.
These appendages play a role in manipulating prey, helping the spider hold and orient its meal during feeding. They also assist in grooming. In male spiders, pedipalps undergo a modification, developing bulbous structures at their tips used to transfer sperm to the female during reproduction. These male palpal structures vary between species, making them important for species identification.
The Feeding Process
Spiders exhibit a unique feeding strategy known as external digestion. After capturing prey, they introduce digestive enzymes into the victim’s body. These enzymes liquefy the internal tissues of the prey into a digestible fluid. Some spiders may also chew their prey with serrated structures on their chelicerae, or regurgitate digestive fluid onto the prey.
Once the prey’s contents are liquefied, the spider uses its sucking stomach (pharynx) to draw the fluid into its body. This muscular pump creates suction, allowing the spider to ingest the pre-digested meal. Fine hairs and filters within the mouth cavity, and a second filter in the pharynx, ensure that only liquid food, free of solid particles, is ingested. This process means spiders primarily consume liquid food, leaving behind the indigestible exoskeleton.
Diverse Mouthparts in Spiders
The appearance and orientation of a spider’s chelicerae and pedipalps vary across different spider groups. A primary distinction lies between mygalomorph spiders, such as tarantulas, and araneomorph spiders, which comprise the vast majority of spider species.
Mygalomorphs possess orthognathous fangs, meaning they are arranged parallel to each other and move in a downward, stabbing motion. In contrast, araneomorph spiders have labidognathous chelicerae, where the fangs cross each other in a pincer-like action, moving from side to side. This difference in fang orientation impacts how spiders capture and manipulate prey. These variations in mouthpart morphology allow different spider species to exploit a wide range of prey types and environments.