Spiders are successful predators with a unique approach to consuming prey. Unlike creatures that chew and swallow solid food, spiders rely on a multi-stage process that first turns their meal into a nutrient-rich liquid. This specialized feeding method is necessary because a spider’s digestive tract is too narrow to accommodate solid matter. The process involves mechanical tools for subduing prey and a powerful chemical cocktail for liquefaction.
Preparing the Meal: Fangs, Chelicerae, and Venom
The initial phase of a spider’s meal begins with its chelicerae, the jointed mouthparts located at the front of its cephalothorax. These chelicerae serve as jaws, and each is tipped with a sharp, hollow fang used to pierce the prey’s exoskeleton.
The primary function of the fangs is to inject venom, which is produced in glands. This venom is a complex mixture of neurotoxins and compounds designed to quickly immobilize the prey. For many species, the venom also contains pre-digestive enzymes that immediately begin breaking down the prey’s tissues. While some spiders crush prey into a pulpy mass, most rely on chemical action for digestion.
The Unique Step of External Digestion
Spiders employ a process called extra-oral digestion (EOD) to prepare their meal, converting the solid contents of the prey into a consumable liquid. To achieve this, the spider releases a potent cocktail of digestive enzymes, which are regurgitated onto or injected directly into the prey’s body.
This digestive fluid is rich in various hydrolases, including proteases, lipases, nucleases, and carbohydrases. These enzymes work to dissolve the internal structures and tissues of the prey, a process known as liquefaction. This chemical action turns the prey’s internal contents into a soup-like substance within its exoskeleton.
Some spiders, known as “refluxers,” repeatedly pump the digestive fluids into the prey and then suck them back up. This constant cycling action improves the mixing and distribution of the enzymes, speeding up the breakdown process. Depending on the size of the prey, this liquefaction can take minutes to several hours, leaving only the indigestible exoskeleton behind.
How Spiders Ingest Liquid Food
Once the prey’s insides are fully liquefied, the spider uses a muscular system to draw the meal into its body. The liquid food enters the narrow mouth opening and passes through the pharynx. The primary mechanical tool for ingestion is the powerful sucking stomach, which is located in the foregut.
This muscular stomach expands and contracts to create a strong vacuum, functioning like a powerful pump to pull the liquid contents from the prey. The ingested food is pulled rapidly into the body due to wavelike contractions of the surrounding muscles. As the fluid is drawn in, it must pass through two sets of internal filters: thick brushes of hairs in the mouth cavity and a second filter in the pharynx. These filtering mechanisms ensure that any remaining solid particles are strained out before the liquid enters the midgut for final digestion and nutrient absorption.