December 2012 Featured Paper

"Morphology and Behavior of Phausis reticulata (Blue Ghost Firefly)" by Jennifer Frick-Ruppert and Joshua J. Rosen, Journal of the North Carolina Academy of Science, 124(4), 2008, pp.139-147
Read the Original Paper

Synopsis

Phausis reticulata, the Blue Ghost, is a firefly mainly of the southern Appalachian Mountains, but can be found as far west as Texas and Oklahoma. It is one of several types of fireflies known as “glowworm fireflies” because the flightless females resemble the larvae. The females produce a constant glow to attract the male, and the males, unlike most other glowworms, produce light as well.

Blue Ghosts are small fireflies - ranging from 0.2 inches to 0.35 inches in length. Females have a transparent exoskeleton and lack wings. They have two light organs on the underside of the abdomen - one near the thorax and the other at the posterior end, although some females have been observed with an extra pair of light organs at the posterior end. These light organs are only evident when lit. The eyes of the female are very small, while males have large eyes that occupy most of the head. The pronotum of the male covers the head and has two transparent areas located directly over the eyes. Males have two light organs at the posterior end of the abdomen.

Seasonal and Nightly Activity
In the sites studied, males first appeared in mid-May and vanished by mid-June. They began to emerge about forty minutes after sunset. Peak activity occurred eighty minutes after sunset, and then declined until nearly nonexistent after midnight. Females were visible only during peak male activity.

Forested areas where moist soil and deep leaf litter are completely covered by the tree canopy seem to be the preferred habitat of these fireflies. Most activity occurs during periods of high humidity. Males do fly during light drizzle, but not heavy rains.

Male Luminescence and Behavior
The males do not flash in any specific pattern, but instead emit a constant glow. They have the ability to turn their light on and off, but show no particular pattern in the timing of the illumination. Their glow appears bluish-white from a distance, but bright green when seen in close range.

Upon first emerging, males fly close to the ground, eventually ascending approximately three feet. Their flight is slow and their flight pattern erratic, each flying independently of the others.

Female Luminescence and Behavior
Far fewer females than males were observed. All were found in shaded areas with thick, moist leaf litter. Like the males, the females emitted a constant glow, but in the female this light is visible through both the underside and top side of their transparent exoskeleton.

Mating Behavior
Females were observed to be selective in their mating choice, refusing to mate with some males. In one instance, the female was seen pressing her abdomen into the leaf litter during the male attempt to mate. After several tries, the male abandoned the endeavor and walked away. When placed in a container with several males, however, the female eventually mated with one.

In one observation, three illuminated males flew directly upwind towards one female. Each extinguished his light as he drew near the female, then dropped to the ground. One male attempted to mate but was denied, while the other two were unable to find the female.

In another instance, several males approached a steadily glowing female. They flew over her without stopping, but one male reversed direction, turned off his light, dropped to the ground, and successfully mated with her.

Response to Stimuli
It is not known whether the males time their activity in response to light levels of the day or from an innate biological clock. Captive males placed in the dark to simulate evening during the daytime remained inactive. Reversing the light/dark cycles had no effect on their activity, which may indicate that circadian rhythms control their behavior.

Shining a bright white light on these fireflies elicited different responses. Some males flew away from the light while others did not, but most ceased glowing for several minutes. Females did not react to the white light and continued to glow even with the light directed on them. Neither males nor females reacted in any way to red or blue light. The researchers then opted to use red light when working in the field so as not to alter the fireflies’ normal behavior.

Tapping a jar containing the fireflies caused two of four males tested to dim then brighten their lights. All females tested lit up when disturbed. This reaction may be a defensive warning to predators, signaling their unpalatability.

Discussion

Many firefly species appear to be declining in numbers due to habitat loss, and the Blue Ghost may be especially vulnerable. Adult females do not fly, and their limited movement restricts their ability to colonize new areas. This relative immobility, coupled with their specific habitat needs as described above, leaves them at risk of population decline with loss of their habitat.

Females apparently advertise themselves to males by glowing. Males locate the glowing female while in flight, then drop to the ground and walk towards her. The male’s glow seems to play no part in the mating process, as females were never seen to light up in response to a male’s glow. The purpose of male luminescence remains unexplained, although it may allow them to interact with other glowing males.

Pheromones may also play a role in mate identification, indicated by the observation of the three males flying directly upwind towards a specific female.


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