In fact, one gnat can lay two to three hundred eggs in its two to four month life span. If you frequently see gnats hovering around your sink drain or trash can, there's a good chance they're laying eggs inside your home. Source(s): http://www.wisegeek.com/how-can-i-get-ri...♥ G ♥ · 9 years ago.eport Abuse. Adults live about 7 to 10 days and deposit eggs on the moist soil surface or in soil cracks. Females lay up to 100 to 300 eggs in batches of 2 to 30 each in decaying organic matter. Eggs hatch in 4 to 6 days; larvae feed for 12 to 14 days.