Many people associate fireflies with warm, humid summer nights in the eastern United States, often wondering if these enchanting insects also grace the skies of Colorado. While their presence might be surprising to some, fireflies do indeed exist in Colorado.
Fireflies in Colorado
Fireflies are present in Colorado, though their populations are generally localized and more dispersed compared to the eastern U.S. These bioluminescent beetles can be found in various regions, including the Front Range, Western Colorado, and Southeastern Colorado. They primarily inhabit moist, wetland areas such as those near creeks, ponds, rivers, lakes, and marshes, often in places well-shaded by trees like cottonwoods. Water diversions and irrigation have also created new wetland habitats that fireflies have colonized.
Several species of fireflies are known to occur in Colorado. Luminescent species, particularly from the Photuris and Photinus genera, have confirmed reports from counties including Weld, Larimer, Boulder, Adams, Pueblo, Yuma, Routt, Alamosa, and Saguache. Photinus pyralis has been specifically identified in Baca County. Non-luminescent species, such as Pyropyga minuta and the Ellychnia corrusca complex, are more common and can be found in irrigated lawns and gardens across eastern Colorado.
Fireflies in Colorado are typically active for a brief period each year, generally from late June through July. They usually begin flashing after 9:00 PM, as the nights warm up. This short adult activity window often lasts only a couple of weeks, making them a fleeting sight.
Spotting a True Firefly
Fireflies, despite their common name, are beetles belonging to the family Lampyridae, not true flies. A distinct feature of adult fireflies is their elongated-oval body shape, which is slightly flattened. Their forewings, or wing covers, are typically dark gray or brown and are relatively soft compared to most other beetles. The prothorax, a broad, plate-like structure, conceals most of their head and is often edged with yellow, red, or orange. Most species range from 10 to 15 mm in size.
Many fireflies produce light, known as bioluminescence. This “cold light,” which generates very little heat, comes from a specialized organ located at the tip of their abdomen. For flashing species, this light-producing organ is typically yellow to yellow-green. The light is created through a chemical reaction involving luciferin, luciferase, ATP, and oxygen.
Fireflies use flash patterns to communicate, primarily for attracting mates. Each species has a unique flash pattern, which can vary in duration, timing, color, and the number and rate of repetitions. Flashes can be yellow, orange, or green, and the timing of these flashes is crucial for species recognition.
Insects Often Mistaken for Fireflies
Several other insects might be confused with fireflies, as not all firefly species produce light as adults, and some nocturnal insects exhibit similar behaviors or appearances. For example, some non-luminescent firefly species, like the Ellychnia corrusca complex, are day-flying and resemble flashing fireflies but lack light-producing organs. These species rely on pheromones for communication.
Glow-worms are another group that can cause confusion. The term “glow-worm” refers to the wingless female fireflies or even the larval stages of fireflies, which can also produce light. Unlike adult fireflies that fly and flash, glow-worms are typically wingless and produce a continuous glow rather than distinct flashes. Their light is often used to attract flying males.
Other beetles, such as certain click beetles or longhorn beetles, might be mistaken for fireflies. Some click beetles can glow, but their light organs are on their head or under their abdomen, and they do not typically flash like fireflies. Firefly-mimicking longhorn beetles can resemble fireflies in size, shape, and color, sometimes even having similar abdominal markings, but they do not produce light.