To combat mosquitoes invading your backyard, be diligent about standing water. Mosquitoes need as little as a tablespoon of water to lay eggs, so take the time to look for potential breeding sites. Things like broken water fountains, birdbaths, pets' water bowls and even clogged gutters can be the perfect habitats. Buckets, watering cans and anything used to hold water should be flipped upside down or drained and dried in the sun. If you have a rain barrel, add a little vegetable oil after a rainstorm; the oil will float to the top and suffocate any mosquito larvae that may be there.