Larval Biology and Ecology of Photuris Fireflies in Northcentral Florida

In north central Florida, at least a dozen species of Photuris fireflies occur in a variety of habitats. Since it is often not possible to identify Photuris species by their physical characteristics, species differentiation is based on the male flash pattern. However, since the flash of Photuris fireflies is more complex than other fireflies, sorting out the taxonomy of Photuris fireflies is unresolved. Identifying the differences in the larval fireflies may help in identifying species and improve our understanding of their biology.

Methods

Larvae of Photuris fireflies were collected from numerous habitats around Gainesville Florida in 1970 and 1971. The habitats included wet, dry and wooded areas. Larvae were collected on warm evenings after a rain throughout the year. Collected larvae were raised in baby food jars with moist sifted sand, and they were fed chicken liver and cut-up insects.
The larvae were split into four groups: groups 1 and 2 were placed in a refrigerator for 36 days and then reared at room temperature. Group 1 was raised with a long day (15 hours of light) and group 2 with a short day (10 hours of light). Groups 3 and 4 were raised only at room temperature. Group 3 was raised with a long day and group 4 with a short day.
Larvae were divided into two groups based on color: red and non-red. The larvae were raised to adult and identified. All red larvae grew into Photuris congener. The non-red larvae grew into a number of species. Since most of the species of Photuris were undescribed at the time of this study, they are only known by code names: "A," "B," "D," "W" and "V."

Results

Photuris larvae were found after dark, glowing periodically as they crawled in leaf litter. Larvae were common when the leaf litter was wet, particularly after a rain that followed a dry spell.

Ecology of Larvae

Red larvae were found in hardwood leaf litter in drier sites. They were collected mostly in August and September.
Non-red larvae were collected throughout the year but were most common in spring and fall. Photuris "A" larvae were collected throughout the year, mostly in areas that were wet all year. Photuris "B" and "D" larvae were collected in early spring and in fall from wooded areas. Photuris "W" larvae were collected in January and March from rotting logs. Photuris "V" larvae were collected throughout the year from wet sites.

Effects of Cold Treatment and Day Length

Differences in day length had no effect on larvae reared at room temperature, but for the larvae exposed to the cold, those with a short day length took longer to reach adulthood.

Soil Excavations

Photuris larvae spent inactive periods in several types of earthen chambers. Molting chambers — used to shed skins in larval growth — were shallow and had thin ceilings raised above the ground surface. Pupating chambers were deeper and had thicker ceilings. Some non-red larvae dug small wedge-shaped holes in which they rested in during the day while some red larvae dug extensive burrows.

Feeding Behavior

Photuris larvae are rarely seen feeding in the wild, but they have been found eating snails and earthworms. The food list for captive larvae is larger and includes snails, slugs, earthworms, larval potato beetles, cutworm larvae, and young squash-bug nymphs. Non-living food includes cut-up insects, Tubifex worms, raw or cooked beef or pork, chicken liver, creamed cheese, boiled egg yolk, grapes, some vegetables, and gelatin.

Identification of Larvae

If Photuris larvae could be identified to species without raising them to adult, it would be much easier to study the field ecology and behavior. During the study, the author was able to identify red larvae as Photuris congener. The non-red larvae produced all other Photuris species. Larvae from Photuris "W" was found only in rotting logs and had uncolored sections on their backs. The remainder of the non-red larvae could not be separated reliably.