Firefly Species and Nocturnal Activity Patterns of Adults in Peri-Urban Forests of Dongguan

Abstract

Against the backdrop of advancing ecological civilization and increasing public interest in reconnecting with nature, this study examines fireflies—iconic insects cherished for their natural charm—as valuable landscape resources. This study was conducted in Dalingshan Forest Park, Dongguan (Pearl River Delta), using the Forest Science Trail as a sampling site. Surveys combining line transect and point count methods were employed to analyze firefly species composition, adult activity patterns, and flight characteristics. Key findings include: (1) Four species were identified—Asymmetricata circumdata, Pygoluciola qingyu, Aquatica analis, and Luciola satoi—three of which were observed along the trail; (2) Adults appeared sporadically after 19:00, with peak activity occurring between 19:30 and 20:00, showing minor interspecific variation; (3) Although flight height varied slightly among species, most activities concentrated within 0–1.5 m, corresponding to herbaceous and shrub layers; (4) Distinct flight patterns were observed: A. circumdata displayed prolonged intermittent flights, while P. qingyu and L. satoi exhibited shorter perching-based flights. These results provide a scientific basis for firefly habitat conservation, biodiversity promotion, and the sustainable integration of firefly landscapes into nature education and ecotourism.

1. Introduction

Fireflies, belonging to the suborder Polyphaga within the order Coleoptera, are collectively referred to as insects of the families Lampyridae and Rhagophthalmidae. Their unique nocturnal luminescence has made them a group of significant interest as nighttime insects in many regions worldwide. Currently, there are approximately 2200 known species of fireflies under 140 genera in the family Lampyridae, and 50 species in 8 genera in the family Rhagophthalmidae [1]. Mainland China is rich in firefly resources, with documented records of 141 species and 1 subspecies under 24 genera and 5 subfamilies of Lampyridae, and 20 species in 1 genus of Rhagophthalmidae [1,2,3]. Fireflies serve not only as environmentally sensitive ecological indicator species but also as unique insect-based landscape resources, combining both ecological value and scenic appeal [4]. However, firefly populations globally are facing threats from habitat loss and environmental degradation [5].

In recent years, with increasing awareness of nature conservation and the prominence of fireflies’ unique landscape value, their protection, restoration, and utilization have become research hotspots in the ornamental insect industry. Studies on fireflies, both domestically and internationally, cover a wide range of areas including resource surveys, ecotourism, flashing behavior, taxonomic identification, artificial rearing, feeding behavior, and habitat characteristics. Considerable experience has been accumulated in the artificial propagation and utilization of firefly resources, making them an important component of nature education and ecotourism [1,6,7,8,9,10,11,12,13,14,15]. Overall, research on the nocturnal activity behavior of adult fireflies has primarily focused on aspects such as activity timing [16,17,18], flashing patterns [19,20,21,22], flight height [23], and environmental influencing factors [24,25]. However, there is a lack of studies examining the behavioral characteristics of firefly activity landscapes from the perspective of human nighttime observation and experience. At the same time, against the backdrop of rapid global urbanization, urban forests provide suitable habitats and food sources for wildlife within cities, and their role in biodiversity conservation is becoming increasingly important [18,26,27,28]. Research on the landscape behavior characteristics of adult fireflies in urban forests holds significant theoretical and practical implications for the conservation of firefly resources and the development of their value for tourism and educational activities.

This study aims to characterize and systematically understand the activity patterns, spatial distribution, and landscape features of different firefly species from a human observation perspective, thereby providing a scientific basis for the conservation of local firefly resources, the design of firefly landscapes, and the development of tourism and educational activities.

2. Materials and Methods

2.1. Study Area

The Dalingshan Forest Park in Dongguan is located in the southwestern part of Dongguan City, Guangdong Province, and northeast of the Pearl River Estuary (113°42′22″–113°48′12″ E, 22°50′00″–22°53′32″ N), with an elevation range of 15–530 m. It is rich in biological resources [29] and represents a large preserved forest patch within Dongguan’s urbanization process. It has become an important ecological and recreational site in Dongguan City and even the central area of the Guangdong-Hong Kong-Macao Greater Bay Area urban agglomeration, serving as a crucial ecological source for biodiversity conservation and restoration in the region.

Based on a comprehensive investigation of the firefly species and their spatial distribution within Dalingshan Forest Park, the survey focused particularly on the Forest Science Trail, where adult fireflies are relatively concentrated and free from human disturbance at night. This Forest Science Trail is a narrow, elongated stream characterized by dense vegetation and a favorable ecological environment, stretching 500 m in length with an average width of 50 m. The area features tall trees and bamboo species such as Erythrophleum fordii Oliv., Syzygium samarangense (Blume) Merr. & L. M. Perry, Taxodium distichum (L.) Rich., Albizia falcataria (L.) Fosberg, and Bambusa textilis McClure. Shrubs include Microcos paniculata L. and Alchornea trewioides (Benth.) Müll. Arg., while herbaceous plants comprise Alpinia zerumbet (Pers.) B. L. Burtt & R. M. Sm., Cyclosorus interruptus (Willd.) H. Itô, Streblus asper Lour., Diplaziopsis cavaleriana (Christ) C. Chr., and Alocasia odora (Roxb.) K. Koch.

2.2. Research Methods

2.2.1. Survey on Activity Patterns of Fireflies

Fireflies undergo a complete metamorphosis life cycle consisting of four stages: egg, larva, pupa, and adult. According to relevant studies [30] and preliminary observations by local firefly enthusiasts in Dongguan, adults typically emerge in large numbers during summer. Pre-surveys in Dalingshan Forest Park indicated that the adult activity period occurs from April to August each year. This study was conducted primarily between April and August 2024, and March to August 2025. A combination of transect and point-count methods [10,31] was employed for the survey. Taking into account factors such as visibility within the stream valley, clarity of identifying flashing characteristics of adult fireflies by sight, and the filming distance for capturing flight behavior, the Forest Science Trail along the stream was evenly divided into 25-m segments from downstream to upstream, establishing 21 sampling points (Figure 1). Observations were carried out daily from 19:00 to 23:00, repeated at 30-min intervals. During the survey, personnel stationed at each sampling point turned off lights for a 1-min dark adaptation period. They then rotated steadily in four directions (front, back, left, right), recording the number of fireflies, horizontal distance, and height above ground (or above the slope surface on inclined terrain) in each direction for 1 min per direction. This observation cycle was repeated three times. Additionally, all-night observations were conducted over a period of three days.

2.2.2. Survey on Flight Characteristics of Fireflies

Firefly flight trajectories were captured using long exposure photography with a Sony camera, while flight patterns were recorded through naked-eye observation.

2.2.3. Survey on Species Identification of Fireflies

This study adopted the live sampling method to obtain firefly samples, with capturing carried out using insect nets or hand capture during the survey period. Species identification was conducted based on morphological characteristics, flight characteristics, and luminescent characteristics; after the completion of identification, the live samples were released back to their original habitats. For species that were difficult to identify morphologically through basic appearance in the field, they were brought back to the laboratory for anatomical identification. During continuous observation, firefly species and abundance were documented based on flight behavior and luminous characteristics.

3. Results

3.1. Species Composition of Fireflies in Dalingshan Forest Park and Its Forest Science Trail

This field survey documented a total of four species of adult fireflies in Dalingshan Forest Park, Dongguan City, namely: Asymmetricata circumdata (Motschulsky, 1854), Pygoluciola qingyu Fu & Ballantyne, 2008, Aquatica analis (Fabricius, 1801), and Luciola satoi Jeng & Yang, 2003 (Figure 2). However, only three species—Asymmetricata circumdata, Pygoluciola qingyu, and Luciola satoi—were observed along the Forest Science Trail. Among them, Asymmetricata circumdata reached a total of 2895 individuals, accounting for 69.78% of the total observed fireflies. Compared to the other three species, it exhibited the highest abundance and widest distribution within Dalingshan Forest Park.

3.2. Temporal Characteristics of Nocturnal Activity of Adult Fireflies in the Forest Science Trail

3.2.1. Seasonal Distribution Characteristics of Firefly Activity

Fireflies in the urban areas of Dongguan City begin to appear sporadically from late March to early April, while adult fireflies in Dalingshan Forest Park start to appear sporadically in early April, usually about one week later than those in urban areas.

Adult fireflies on the Forest Science Trail are present from April to August. In terms of the seasonal distribution of population size: adult fireflies first appear sporadically in early April, their population size gradually increases by mid-April, reaches the peak in mid-May, maintains the peak period from mid-May to early June, slowly decreases from early June to mid-June, and then appears sporadically after mid-June, persisting until August (Figure 3).

Regarding the sequential appearance of adult fireflies of different species, Asymmetricata circumdata was sporadically observed in early April, reached its peak abundance in mid-May, and became sporadic again after mid-June, with individuals persisting until mid-to-late June. Pygoluciola qingyu began to appear sporadically in early April, maintained high abundance from May to June, and gradually declined in July until August. Luciola satoi started to emerge in mid-to-late May, reached its peak at the end of May, began to decline in mid-June, and continued sporadically until late July or early August (Figure 4).

3.2.2. Overall Rhythm of Fireflies’ Nocturnal Activity

In terms of the nocturnal activity of fireflies throughout the night, adult fireflies are generally active from 19:00 to 06:00 the next day, with the highest population density occurring between 19:30 and 20:00, accounting for 13.36% of the total number observed throughout the entire observation period. From the perspective of the current public night viewing period for adult firefly landscapes in Dongguan City, 19:00–23:00 is typically the ideal time for the public to view fireflies, and this is also the peak occurrence period of adult fireflies (Figure 5).

From the perspective of the peak nocturnal activity period of adult fireflies on the Forest Science Trail, the peak nocturnal activity period of fireflies is generally 19:30–21:30. Among this period, fireflies appear sporadically from 19:00 to 19:30; their population quickly reaches a peak around 20:00 and persists until 21:00. After 21:00, the number of fireflies decreases rapidly, and they appear sporadically after 22:00 (Figure 6).

3.2.3. Nocturnal Activity Rhythms Among Firefly Species

Asymmetricata circumdata (Motschulsky, 1854) began to appear between 19:00 and 19:30, with its peak occurrence from 19:30 to 20:00. After this period, the number of individuals started to decline, and only sporadic appearances were observed after 22:00. Through three overnight surveys, it was found that A. circumdata could appear from 7:00 PM until around 1:00 AM the following day; no flashing activity was observed after 1:00.

Pygoluciola qingyu Fu & Ballantyne, 2008 started to appear between 19:00 and 19:30, with its main activity period occurring from 19:30 to 21:30. The population reached its peak between 20:00 and 20:30, followed by a gradual decline. After 21:30, the number decreased rapidly and continued until 5:30–5:50 the next morning. However, based on three full-night surveys, it was observed that most individuals of P. qingyu seldom changed positions, staying in the same location and flashing synchronously throughout the night until early morning. The sharp decline in records after 21:30 may be attributed to a reduction in flashing frequency and lower courtship activity after this time.

Luciola satoi Jeng & Yang, 2003 began to appear between 19:00 and 19:30, with its main activity window from 20:30 to 21:30. After 21:30, L. satoi was no longer observed. Given its relatively small population size, the disappearance of L. satoi after 21:30 may also be related to its overall low abundance (Figure 7).

3.3. Flight Height Characteristics of Fireflies in the Forest Science Trail

3.3.1. Overall Characteristics of Fireflies’ Flight Height

In terms of flight altitude, fireflies primarily flew within a range from near the ground up to 5 m above the surface. The majority (50.96% of observed fireflies) were recorded at heights between 0 and 0.5 m, followed by 0.5–1 m (16.29%), and then 1–1.5 m (9.12%). The proportion of fireflies observed between 1.5 m and 5.5 m was relatively low and fairly even, ranging between 1% and 4% for each interval, with even fewer individuals observed at higher altitudes (Figure 8).

When correlating firefly flight altitude with the vertical structure of the forest vegetation, the distribution of fireflies across different forest layers—based on nightly flight observations—showed a clear pattern: the herbaceous layer had the highest abundance, followed by the shrub layer, the sub-canopy, and finally the canopy layer. This indicates that firefly flight activity is predominantly concentrated within the understory vegetation, specifically the herbaceous and shrub layers.

From the perspective of flight behavior, one of the primary purposes of male firefly flight is to locate females. The presence of bare ground patches and shrubbery—potential habitats for female fireflies—may induce males to make approach flights, which can influence their flight altitude [32]. Since fireflies rely on bioluminescent communication and require mutual visibility, males often patrol repeatedly in more open spaces between grasses and the canopy. This behavior increases their chances of detecting and observing females. The height of the herb and shrub layers provides a suitable environment for males to locate and communicate with females resting in the vegetation.

3.3.2. Flight Height Characteristics of Different Species of Fireflies

The three firefly species observed along the forest education trail exhibited significant differences in flight altitude (Figure 9).

(1) Asymmetricata circumdata was predominantly recorded at heights of 0–0.5 m, accounting for 37.71% of its total observations, followed by 0.5–1 m (18.85%), and 1–1.5 m (10.59%). Field observations indicate that females of A. circumdata typically remain in the herbaceous layer, while males fly through the understory searching for females and engaging in flashing communication. This behavior explains their prevalence at low altitudes (0–0.5 m). Additionally, A. circumdata demonstrated stronger dispersal capability compared to the other two species, which also contributes to its presence across multiple height intervals.

(2) Pygoluciola qingyu exhibited a strong concentration at 0–0.5 m, making up 79.08% of observations, with 0.5–1 m as the second most common range (11.68%). This species was often observed perched motionless for extended periods on the tips of fern fronds, which within the forest education trail are mostly within 0–0.5 m, explaining its prevalence at this height.

(3) In contrast, Luciola satoi was most frequently observed at 3–3.5 m (25.93% of individuals), followed by 4–4.5 m (18.52%), and 0–0.5 m (14.81%). Field surveys suggest that L. satoi often perches on trees at heights of 3–5.5 m or on ground-level leaf litter, reflecting its preference for higher and more varied flight altitudes compared to the other species.

Figure 9. Percentage distribution of flight altitudes for three firefly species along the Forest Science Trail. Note: Flight altitude refers to the height of the firefly above the ground.

Figure 9. Percentage distribution of flight altitudes for three firefly species along the Forest Science Trail. Note: Flight altitude refers to the height of the firefly above the ground.

3.4. Flight Characteristics of Fireflies in the Forest Science Trail

3.4.1. Flight Types of Fireflies

Firefly flight patterns were categorized into prolonged continuous-intermittent flight and brief resting-intermittent flight.

Prolonged continuous-intermittent flight refers to the ability of an individual firefly to sustain continuous flight for a relatively long period exceeding three minutes without any resting behaviour. Brief resting-intermittent flight is characterized by short bursts of flight, typically lasting less than one minute, after which the firefly lands and remains stationary for a relatively extended period without immediately taking off again. After this resting phase, the firefly may engage in another short flight.

In terms of flight duration among different species:

Asymmetricata circumdata exhibits prolonged continuous-intermittent flight, using flight and flashing to locate mates.

Pygoluciola qingyu displays brief resting-intermittent flight. Individuals often perch on the tips of leaves along streams and fly infrequently.

Luciola satoi also demonstrates brief resting-intermittent flight. It can be found perching in various forest strata—including the herbaceous layer, shrub layer, sub-canopy, and canopy—though it primarily remains on trees or leaf litter along valley streams.

3.4.2. Flight Trajectories of Fireflies

Based on the flight trajectory diagrams of adult fireflies from different species (Figure 10), distinct patterns can be observed:

The flight trajectory of Asymmetricata circumdata is relatively smooth, appearing as a flickering dotted curve with wide spacing between points. The paths often take an “S”-shape or a straight-line (“—”) pattern.

Pygoluciola qingyu exhibits flight trajectories characterized by flickering, gently undulating segments. Their flight path is irregular and not fixed.

Luciola satoi displays flight trajectories composed of flickering, irregular dotted curves with small intervals between successive points.

4. Discussion

4.1. Habitats of Dalingshan Forest Park and Its Forest Science Trail and the Maintenance of Firefly Diversity

From the survey results, among the four recorded firefly species in the Dalingshan Forest Park, Luciola satoi Jeng & Yang, 2003 was newly discovered during this investigation and had not been previously documented in Dongguan City. This finding enriches the firefly species diversity in Guangdong Province. However, it was also noted that within the Forest Science Trail, three main firefly species were observed, while Aquatica analis (Fabricius, 1801) was not present, although it had been observed in the surrounding areas of the trail in earlier surveys. This indicates that the Forest Science Trail investigated in this study plays a significant role in maintaining the local firefly biodiversity, while certain specific firefly species may have been affected by environmental changes in recent years.

Furthermore, all three firefly species within the Forest Science Trail were found in the upper reaches of the valley, sharing the same habitat. This suggests, to some extent, that valley habitats may provide favorable support for firefly diversity. Pygoluciola qingyu Fu & Ballantyne, 2008 was predominantly concentrated on ferns near the valley, while Luciola satoi Jeng & Yang, 2003 was mainly observed on trees in the valley vicinity. The frequent occurrence of fireflies on certain specific plant species may indicate a preference, warranting further investigation into the relationship between fireflies and plants in future studies.

4.2. Nocturnal Activity Period of Fireflies

In contrast to prior research predominantly focused on the crepuscular luminous behavior of fireflies, this study—through continuous all-night monitoring—confirms that Pygoluciola qingyu exhibits a consistent whole-night luminescence. This finding not only challenges the conventional perception that “fireflies are primarily active during dusk” but also provides critical temporal insights for firefly conservation management and the development of ecotourism. The recommended peak viewing time for fireflies is from 19:30 to 21:00. Depending on the nocturnal activity patterns of various firefly species and human activity preferences, the viewing period may be appropriately extended until 23:00.

Furthermore, it was observed that compared to Asymmetricata circumdata, Pygoluciola qingyu engages in less flight activity and frequently remains perched on vegetation. This low-energy perching strategy may supply the necessary energy for sustaining all-night luminescence. However, it is noteworthy that although Luciola satoi displays similar behavior—reduced flight and prolonged resting on plants—it does not emit light throughout the night. This suggests that energy expenditure is not the sole determinant.

Furthermore, subtle differences in courtship behaviors were observed among the three firefly species. Nocturnal activity timing is likely associated with mating behavior, as the difficulty of males locating females may influence temporal patterns. However, this study did not explore in depth the effect of courtship behavior on luminescence duration, which warrants further investigation.

4.3. Flight Height of Fireflies and Habitat Vegetation Management

As bioluminescent insects highly dependent on vegetation cover and structure for survival and reproduction, firefly population abundance, spatial distribution, and behavioral patterns are significantly influenced by habitat vegetation type and configuration [22]. This study quantified the flight heights of fireflies and concluded that their preferred flight levels are within the herbaceous and shrub layers. This finding offers new insights into understanding firefly habitat selection and provides guidance for vegetation management in firefly habitats—such as recommending the preservation of herbaceous and shrub layers and reducing the clearance of litter layer.

Furthermore, different categories of fireflies exhibit distinct flight heights, revealing adaptive microhabitat selection among various groups. This discovery offers precise optimization directions for firefly habitat management: vegetation management and microhabitat creation should be tailored according to different firefly groups to provide suitable habitats.

Compared to traditional “neat-and-tidy” vegetation management approaches, this vegetation structure design based on flight height preferences can effectively construct microhabitats that meet the ecological needs of fireflies, thereby providing crucial spatial support for population restoration.

4.4. Extending the Firefly Viewing Season: Preliminary Strategies and Ideas

The peak activity period of fireflies in Dongguan City is concentrated in mid-May. Among them, Asymmetricata circumdata—due to its large population size, wide distribution, and strong dispersal capacity—acts as a key species determining the timing of this peak period. The occurrence times of different firefly species vary significantly. Through scientific allocation of habitat resources and staged conservation measures, effective continuity of viewing periods among species can be achieved, thereby significantly extending the firefly viewing season and further expanding the economic window for ecotourism.

It is noteworthy that considerable differences exist in the population sizes among various firefly species. Dominant species such as Asymmetricata circumdata utilize broad adaptability to occupy core resources, while rare species achieve coexistence through specialized ecological niches (e.g., specific host plants or microhabitats). Species with very small populations may be limited by habitat fragmentation, leading to isolation and disrupted connectivity. Studying the activity patterns of each firefly species and creating suitable habitats tailored to different species could potentially enhance their population sizes.

5. Conclusions

Through continuous observation of nocturnal firefly activity along the Forest Science Trail in Dalingshan Forest Park, the following preliminary findings have been revealed:

(1) Although four species of fireflies—Asymmetricata circumdata, Pygoluciola qingyu, Aquatica analis, and Luciola satoi—are distributed in Dalingshan Forest Park, Aquatica analis was not observed along the Forest Science Trail.

(2) In terms of nocturnal activity patterns, fireflies were observed throughout the entire night. Specifically, they began to appear after 19:00, with the peak activity period occurring between 19:30 and 20:30. While the emergence timing did not differ greatly among species, slight variations were observed in peak periods: Asymmetricata circumdata reached its peak earliest, followed by Pygoluciola qingyu and Luciola satoi. Notably, Pygoluciola qingyu exhibited a unique capacity for sustained luminescence throughout the night.

(3) The flight height of fireflies was concentrated within 0–1.5 m above ground. Minor differences were detected among species, with Asymmetricata circumdata generally flying the highest and farthest.

(4) The three observed species also displayed distinct flight patterns and trajectories: Asymmetricata circumdata exhibited prolonged continuous intermittent flight, while Pygoluciola qingyu and Luciola satoi displayed brief sedentary intermittent flight.

Future management efforts should rationally schedule viewing times and protection measures based on fireflies’ luminescence schedules, and implement vegetation maintenance tailored to their preferred flight heights. These findings provide actionable scientific support for the refined management of firefly habitats and the sustainable development of ecotourism.