Fennel is used as a food plant by the larvae of some Lepidoptera species including in its native range the mouse moth and the Old-World swallowtail. Where it has been introduced in North America it may be used by the anise swallowtail. The word "fennel" developed from the Middle English "fenel" or "fenyl". This came from the Old English "fenol" or "finol", which in turn came from the Latin "feniculum" or "foeniculum", the diminutive of "fenum" or "faenum", meaning "hay". The Latin word for the plant was "ferula", which is now used as the genus name of a related plant. The
Fennel of Life" repeatedly refers to the plant and mentions its purported ability to strengthen eyesight: Fennel, "Foeniculum vulgare", is a perennial herb. It is erect, glaucous green, and grows to heights of up to , with hollow stems. The leaves grow up to long; they are finely dissected, with the ultimate segments filiform (threadlike), about wide. (Its leaves are similar to those of dill, but thinner.) The flowers are produced in terminal compound umbels wide, each umbel section having 20–50 tiny yellow flowers on short pedicels. The fruit is a dry seed from long, half as wide or less, and