• ‘Turn off your outside lights. It’ll help fireflies find a mate, which is good for next summer’s populations.
• Plant some native trees in your yard. The larva of some species grows in rotten logs and forest canopy litter, so let the natural litter around them accumulate.
• Add water features to your landscaping. Most fireflies thrive around standing water. That doesn’t, however, include swimming pools: Fireflies eat the grubs, snails and smaller insects around natural ponds and streams, and those food sources don’t live in chemically treated environments.
• Skip the chemicals. Even if fireflies don’t ingest a chemical pesticide directly, they will likely ingest other insects that have been poisoned. Instead, opt for natural options, especially for lawn fertilizers.
• Don’t over-mow the lawn. It’s where a lot of fireflies hang out during the day, and frequent mowing can disturb them. In fact, planting long grasses can attract even more fireflies to your yard….’

— via Lifehacker