Dark brown or rusty excrement (spots of dried blood) on mattresses, as seen here, could mean that you have bed bugs.

M. Potter, University of Kentucky

• Red, welt-like bites that itch and occur while sleeping
• Dark brown or rusty excrement (spots of dried blood) on mattresses, linens or near the bed
• A peculiar musty, sweet odor may be present in heavily infested areas.
• Insects found in cracks and crevices in bedding, nearby furniture, drapes, carpeting, or behind headboards and picture frames, etc. Bed bugs prefer wood and fabric surfaces to metal and plastic. 

Bed bugs can also infest hotels, motels, and other public buildings, so you might want to look for similar signs before you tuck in for the night.

Once a pest control professional has determined you have a bed bug infestation, you need to consider carefully your options for bed bug treatments for your home.