A wood-boring insect or worm.

1

1789.  [The teredo.] I should conceive it a preservative against the Borer, so destructive to ships.—Phil. Transactions, lxxix. 68. (N.E.D.)

2

1789.  The dismal ravages [to the harvest of sugar] made among the canes by a most pernicious insect, called the borer.—Letter from St. Kitt’s, Feb. 13: American Museum, v. 414 (April).

3

1867.  

                    I some misdoubt
’T was borers, there ’s sech heaps on ’em about.
J. R. Lowell, ‘Fitz-Adam’s Story.’    

4