Tabla de Contenidos
Fireflies are insects in the order Coleoptera and the family Lampyridae . Only in the American continent they are represented by at least 1134 species belonging to 40 genera and four subfamilies: Pterotinae , Amydetinae , Lampyrinae and Photurinae .
Lampyrids have nocturnal habits and are distributed in places with warm and temperate climates. Because several species are aquatic, semi-aquatic, or thrive in humid environments, it is common to find fireflies in wetlands or near swampy areas.
Courtship
Fireflies are animals that are distinguished from other Coleoptera by their bioluminescence , that is, by their ability to produce light. This is possible thanks to the fact that they have specialized cells located under the abdomen in which a substance called luciferin is stored, which produces light in the presence of oxygen. Scientists have found that bioluminescence is key during pre-mating courtship.
In general, males are active at dusk. In some species it has been detected that they produce two types of courtship lights: the first consists of 8 fast flashes followed by 2 to 3 slow flashes, all long-range; the other type is the emission of a short-range green glow, which is only emitted when they have located a female.
Once the male and female meet, the male’s courtship pattern changes, flashing longer durations. Meanwhile, females produce response flashes after the male flash.
Metamorphosis
Fireflies are holometabolous insects , that is, they present complete metamorphosis characterized by four stages of development: egg, larva, pupa, and imago. The larvae are totally different from the adults, both in their anatomy and their ecology, and the pupae are immobile.
Depending on the species, the life cycle of fireflies lasts up to 2 years. The common European firefly, the most studied so far, lays its eggs in August, which hatch about a month later. From September to February the larvae are very active and have nocturnal habits; in March they go through the first of four to seven molts, reaching their final size in October. At the end of June of the following year, the larvae are ready to enter the pupal stage, which lasts approximately 10 days in females and 15 days in males. Adults only live for 1 to 2 weeks.
Taking into account that the adults emerge every two years, the same ecosystem will be occupied by two different populations that will not meet: the one in even years and the one in odd years.
The characteristics of each stage of development are described below.
Eggs
Depending on the species, two to four days after mating, females oviposit (ie, lay) between 30 and 200 eggs. It is believed that the number of eggs that the female oviposits is related to her weight when she was in the pupal stage.
In general, these eggs are spherical, measuring 0.8 – 1 mm, and their diameter is 1.1 mm. In some species, the eggs are creamy yellow in color and then become transparent and luminescent 2–3 days after being laid and until they hatch , i.e. until they hatch. In other cases, the eggs become luminescent only up to 4 or 5 days before hatching. There are eggs that hatch in 15 days, others in a month.
larvae
The larvae are immature individuals that emerge from the eggs after hatching and generally do not resemble adult individuals; during this stage of metamorphosis, which lasts up to 22 months, individuals grow and feed.
Morphology. In many species of fireflies, the larvae go through four to six instars, or stages. Each stage ends with a molt, at which time the skin opens and the individual gains size.
Thus, a first-stage larva measures about 2.7 mm and on the surface of its belly it has several setae (that is, hair-like structures) that are long and thick. It differs from mature larvae in that its body is not pigmented; also in their jaws, in the middle of which is a serrated tooth-like structure called the retinaculum .
In contrast, a sixth instar larva measures about 12.2 mm. Its head is prognathous , that is, located more or less in the same plane as the body, so its mouthparts are directed forward. Generally, the surface of its back is dark brown, with a pair of elongated, yellowish lateral spots, covered by tiny, whitish setae. Meanwhile, the surface of his belly is yellow, almost without setae; and the abdomen presents a row of thick setae.
Habitat. Most of the larvae are terrestrial, few species are aquatic or semi-aquatic. They are usually found among submerged vegetation and under decaying logs, where they emit light signals as a preventive measure or to attract their prey, on which they feed voraciously.
Feeding. The larvae are predatory. They eat worms, small insects, snails, and slugs. To do this, they have sickle-shaped jaws that allow them to inject digestive substances into their prey. Some species produce defensive substances called lucibufagins that cause vomiting in their predators.
pupa
Pupae are the last stage of metamorphosis in holometabolous insects such as fireflies. Some species suppress this phase, a phenomenon known as neoteny or paedomorphosis , which consists of maintaining juvenile characteristics when sexual maturity is reached. The rest of the species exhibit pupae that are housed in the emergent vegetation.
In certain species the pupae are luminescent, just as they were when they went through the egg and larval stages. Most of the pupae remain motionless and are heavily pigmented yellow, dark brown, or brown in color.
Various studies have reported that the duration of the pupal stage is related to sex, so that males remain in this stage between 6.8 and 15 days, while females remain as pupae for approximately 6.4 to 10 days.
Adult
Morphology. Adult fireflies measure between 10.0 – 10.6 mm. The first segment of the midbody, called the pronotum , is semicircular and slightly convex. In some species the forewings or elytra are dotted, brown in color, with yellow margins. The front part of the thorax or prothorax is yellow; the head, antennae and legs are brown; the head has antennae. In males, the luminescent organs occupy the ventral segments or ventrites 5, 6 and 7; in females these organs are located in ventrites 5 and 6, while ventrite 7 is triangular and rigid.
Feeding. Adult fireflies no longer feed, only living off the reserves they accumulated during their voracious larval stage. This is because their only goal is to reproduce, so this life stage only lasts 1-2 weeks.
sexual dimorphism. Dimorphism refers to the presence of observable characteristics in adult individuals that allow differentiating males from females.
In several species of fireflies, the females resemble larvae, because their body is elongated and flattened and they do not develop or have little developed wings, for this reason they are known as “light worms”. However, in these cases, the females differ from the larvae in that they do not have the yellow spots that are observed at both ends of each segment of the individuals in the larval stage. In addition, the females only appear during the summer, while the larvae can be seen in all four seasons.
On the other hand, males may be smaller than females, have wings and eyes that are better developed than females to discern light contrasts during courtship.
Sources
Fu, X., Nobuyoshi, O., Vencl, F., Lei, C. Life cycle and behavior of the aquatic firefly Luciola leii (Coleoptera: Lampyridae) from Mainland China . The Canadian Entomologist . 138(6):860-870 DOI: https://doi.org/10.4039/n05-093 , 2006.
Gutiérrez, P. Illustrated guide for the ecological and taxonomic study of aquatic insects of the Order Coleoptera in El Salvador. In: Springer, M. & JM Sermeño Chicas (eds.). Formulation of a standardized methodological guide to determine the environmental quality of the waters of the rivers of El Salvador, using aquatic insects . Project University of El Salvador (UES) – Organization of American States (OAS). UES University Publishing House, San Salvador, El Salvador. 64 p, 2010.
Guzmán, JR, De Cock, R. Have you seen a firefly? controlbiologico.info, 2011.
Lanuza, A., Santos, A., Barria, E., Hernández, G., Osorio, M. Predation of the “slug” Veronicella cubensis Pfeiffer (Mollusca: Gastropoda: Veronicellidae), by the larva of Cratomorphus signativentris Olivier 1895 ( Coleoptera: Lampyridae) in Panama . Technoscience . 23. 10.48204/j.tecno.v23n1a18, 2020.
