The bugs, bacteria, and nasties are sucked into the first millimeter or so of the wood and are trapped there.
And let's say President Assad's nasties kill them in droves.
c.1400, "foul, filthy, dirty, unclean," of unknown origin; perhaps [Barnhart] from Old French nastre "miserly, envious, malicious, spiteful," shortened form of villenastre "infamous, bad," from vilein "villain" + -astre, pejorative suffix, from Latin -aster.
Alternative etymology [OED] is from Dutch nestig "dirty," literally "like a bird's nest." Likely reinforced in either case by a Scandinavian source (cf. Swedish dialectal naskug "dirty, nasty"), which also might be the source of the Middle English word. Of weather, from 1630s; of things generally, "unpleasant, offensive," from 1705. Of people, "ill-tempered," from 1825. Noun meaning "something nasty" is from 1935. Related: Nastily; nastiness.
Good; stylish; admirable (1834+)noun