Extra-oral digestion

Definition

A feeding process in which digestive enzymes are secreted onto or injected into food outside the body, liquefying or partially breaking down tissues before ingestion; the resulting fluid or partially digested material is then imbibed.

Etymology

Example

Spiders inject venom containing proteolytic enzymes into prey, then pump the liquefied tissues from the exoskeleton; similarly, many predatory Hemiptera such as assassin bugs (Reduviidae) inject saliva that externally predigests insect prey before sucking up the fluids.

Synonyms

• external digestion
• pre-oral digestion

Related Terms

• sanguivory
• fluid feeding
• Proboscis
• salivary gland
• enzymatic venom
• Trophic egg

Usage Notes

Distinguished from intra-oral digestion (typical chewing and gut-based processing) and from simple fluid feeding that lacks enzymatic modification of food. The term is absolute, not relative; a predator either employs extra-oral digestion or does not, though the degree of external liquefaction varies. Some authors restrict the term to cases where enzymatic breakdown is substantial rather than minor salivary softening. Common in fluid-feeding arthropods including spiders, solifuges, many true bugs, and some larval beetles, but absent in most mandibulate chewers.