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The Two Meanings of "Leech": Biological Parasite and Human Parasite
Leech operates in two distinct semantic domains—literal and metaphorical—both invoking attachment and extraction.
1. Literal: The Medicinal & Wild Leech
- Taxonomy: Phylum Annelida, Class Clitellata, Subclass Hirudinea. ~600 species.
- Anatomy: Segmented body, anterior/posterior suckers, three jaws with ~100 teeth each (medicinal leech Hirudo medicinalis).
- Feeding: Hematophagous; saliva contains hirudin (thrombin inhibitor), calin, hyaluronidase, anesthetics.
- Medical Use (Hirudotherapy): FDA-cleared for venous congestion in replantation/flap surgery; osteoarthritis pain (off-label). Applied 1–7 days; each leech consumes 5–15 mL blood.
- Risks: Aeromonas infection (prophylactic ciprofloxacin), prolonged bleeding, anemia, allergic reaction.
2. Metaphorical: The Human Leech
- Definition: A person who habitually exploits others' resources (money, time, labor, emotion) without reciprocity, often through manipulation, guilt, or dependency.
- Synonyms: Freeloader, sponger, parasite, moocher, bloodsucker, user.
- Contexts: Family (adult child not contributing), workplace (credit-taker), friendship (emotional vampire), politics (corrupt official), finance (predatory lender).
Contrastive Examples
| Sentence | Meaning |
|---|---|
| "The surgeon applied medicinal leeches to the congested flap." | Literal: therapeutic hirudotherapy. |
| "He's a leech who never pays rent but eats all the food." | Metaphorical: human exploiter. |
| "The leech dropped off when satiated." | Literal: biological behavior. |
| "She leeched off her parents' savings for a decade." | Metaphorical (verb): to exploit persistently. |