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The light of fireflies in the night sky signal summer in many regions. But more and more groups are raising concerns about the dwindling numbers of these treasured insects. Don Salvatore, coordinator of the Firefly Watch, a Citizen Science Project at the Museum of Science, in Boston, is researching the disappearance of firefly populations, starting with those in residential yards. Ben Pfeiffer, firefly conservationist and founder of Firefly.org, is involved in the restoration of those populations.

Luring fireflies to your yard can take time and, depending on where you live, might even be impossible. Read on to learn about the different types of fireflies, to figure out if your yard can support them, and to find tips from Pfeiffer and Salvatore about how to attract fireflies to your yard.

Firefly 101

There are over 150 species of firefly in the U.S., each with its own environment, Salvatore says. Of those 150, there are three main types: Photurinae give off short flashes, Lampyrinae give off an extended glow, and Otetrinae send out pheromone signals instead of light. The first type is the one most commonly associated with fireflies and is found mainly east of the Rockies.

Fireflies relocate very slowly, say Pfeiffer and Salvatore. Even if you live in the Eastern U.S., there's no guarantee that you can turn your yard into a glowing oasis. But fireflies do change their habitat if a more ideal environment crops up nearby. If you already have them, follow these tips to try to keep them. If you've hosted them in the past, make these changes to attract them to your yard again.

1. Turn off artificial lights

Because firefly light is fairly dim, bright exterior and interior lights hamper your view of the bugs' natural bulbs and also obstruct the fireflies' signals to one another, Salvatore says. Males fly around blinking to attract females, who respond with a signal from their perches in trees or on the grass. A firefly's glow also warns predators, "Do not eat me." To see the fireflies you attract to your yard, dim your lights at dusk and turn them off at bedtime.

2. Go natural

"Keep your yard as ecological as possible," Salvatore says. First, avoid using pesticides or lawn chemicals on your grass because they may harm the larvae, as well as the slugs, snails, and worms they eat. Second, let part of your yard grow naturally. If you want to attract fireflies to your yard, Pfeiffer recommends setting aside a portion of your lawn that you'll mow about only once a year. Longer grass provides a cover for larvae and the bugs they also feed on. Taller blades also give female fireflies a better vantage point at night, when they crawl up to watch out for male mates in the sky.

3. Add water

Fireflies need water to survive. Any sort of moisture will do, says Pfeiffer, whether it's from "man-made ponds, small depressions in the yard, or standing water." Even dew on a branch helps. More often, however, providing the right environment for fireflies boils down to weather and region. For instance, Pfeiffer, who is based in Texas, says this year's rain and humidity have made it a great time for fireflies there.

4. Repel pests—the safe way

Because of the moisture requirement, where there are fireflies, there are often mosquitoes, Salvatore says. If you must debug, choose methods that are less likely to kill off fireflies and their food sources. Salvatore suggests mosquito pellets; the bacteria in the pellets attack mosquito larvae. From what he has read, it's unlikely the pellets will harm fireflies. Pfeiffer puts natural garlic-based spray and citronella oil on the list of safe products that shoo away unwanted suckers.

5. Grow a garden

Vegetable gardens are great for fireflies, Pfeiffer says. The soil is often tilled and moist—an ideal environment for fireflies to lay eggs. Don't worry, the eggs won't harm your crops. Tilled soil also attracts insects like worms, snails, and slugs, the all-star diet for firefly larvae.