Related Clues:

• Secret observers
• Works in intelligence
• Thorns in one's side
• Gnats and mice
• They're annoying
• Termites and such
• 41-Across, e.g.
• Gnats and moles
• Gnat and rat
• Raid victims
• They may be hard to get rid of
• Moles, e.g.
• Nathan Hale and others
• Swattable sorts
• Mosquitoes, e.g.