The Dark Side of the Light Show: Predators of Fireflies in the Great Smoky Mountains

Hindawi Publishing Corporation Psyche Volume 2012, Article ID 634027, 7 pages doi:10.1155/2012/634027 Research Article The Dark Side of the Light Show: Predators of Fireflies in the Great Smoky Mountains Sara M. Lewis,1 Lynn Faust,2 and Raphaël De Cock3 1 Department of Biology, Tufts University, Medford, MA 02155, USA 2 Emory River Land Company, 11828 Couch Mill Road, Knoxville, TN 37932, USA 3 Evolutionary Ecology Group, University of Antwerp, 2610 Antwerp, Belgium Correspondence should be addressed to Sara M. Lewis, Received 14 July 2011; Accepted 15 September 2011 Academic Editor: Diana E. Wheeler Copyright © 2012 Sara M. Lewis et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In the Great Smoky Mountains of East Tennessee, the Light Show is a popular seasonal attraction created by thousands of courting male Photinus carolinus fireflies (Coleoptera: Lampyridae) that flash in synchrony to locate females. This study was undertaken to provide a temporal snapshot of whether invertebrate predators are active within these dense and conspicuous firefly breeding aggregations. In addition, we examined whether female Photuris fireflies, which are specialist predators on other fireflies, show any feeding preferences within the diverse local firefly fauna. A field survey revealed a surprisingly diverse suite of generalist insectivores feeding on fireflies within P. carolinus breeding aggregations. In addition, laboratory studies revealed major differences in prey consumption rates when Photuris predators were given access to several lampyrid taxa. This suite of generalist and specialist predators appears to create a complex selective landscape that is predicted to be a powerful force shaping the evolution of firefly defenses. 1. Introduction Animals with conspicuous courtship displays that breed in dense aggregations are expected to be targeted by many predators [1, 2]. Fireflies (Coleoptera: Lampyridae), however, have a reputation for being distasteful to many potential predators [3, 4]. Several lampyrid taxa have been shown to contain chemicals that confer protection against generalist insectivores such as birds, spiders, and ants [5–7]. While lists have published tallying instances of observed predation on various fireflies [3, 8], no study has described the predator guild active within a firefly breeding aggregation at a single location and season. In North America, Photuris fireflies are specialist predators that eavesdrop on the courtship signals of other fireflies [9–12]. Photuris females have been shown to be voracious predators of certain Photinus fireflies [3, 13, 14], from which they sequester defensive compounds known as lucibufagins [6]. Lloyd [3, 10] reviewed numerous field observations of Photuris females preying upon several firefly species. Eisner et al. [6] reported lab studies in which 6 Photuris females each ate 2 Photinus ignitus males, and a study by Gronquist et al. [15] found that 5 Photuris females each ate 3 Lucidota atra fireflies, a diurnally active species that also contains lucibufagins. To date, however, no systematic study has been made of the feeding proclivities of these predatory Photuris fireflies. The Great Smoky Mountains in East Tennessee host a diverse and abundant lampyrid fauna, including both diurnal and nocturnal species [16, 17]. Among these are Photinus carolinus, a species in which thousands of males gather in dense aggregations and flash synchronously to locate females [18, 19]. In the Great Smoky Mountains National Park (GSMNP), this phenomenon is popularly known as the Light Show. During their 2-week mating season in June, these fireflies attract close to 30,000 park visitors. Such aggregations might be expected to attract many predators as well. Faust [19] reported that P. carolinus males were often caught in webs of Araneidae spiders, and harvestmen (Opiliones: Phalangiidae) was found carrying dead P. carolinus. Another abundant nocturnal firefly, Phausis reticulata, is also active in this rich alluvial montane habitat at the same time of night. Commonly known as blue ghost fireflies, these males fly slowly over the forest floor emitting a bluegreen flickering glow. However, to date there has been no systematic survey describing the common predators of these two firefly species which are so popular with park visitors. 2 This study was conducted during the P. carolinus mating season with the goal to survey invertebrate predators of P. carolinus and Phausis reticulata adults and also to determine whether specialist Photuris predators differentially prey on various firefly taxa. 2. Methods 2.1. Field Surveys of Firefly Predators. Field observations were conducted at GSMNP by walking along a ∼4 km path through P. carolinus breeding aggregations from 2000 to 2400 h during the peak display season (4–19 June 2011). Our surveys were conducted in Sevier Co. at Elkmont, Tennessee (35◦ 39 13 N, 83◦ 34 50 W), although this species is found throughout the park in second growth hardwood forests at about 750 m elevation [19]. Male courtship signals in P. carolinus consist of flash trains containing 4–8 pulses given at 0.5 sec intervals, followed by 6–9 sec of darkness; females respond to male advertisements by emitting a doublet flash approximately 3 sec following final pulse in a male’s flash train [19]. We detected predation by looking along the ground and on vegetation for the distress flashes given by P. carolinus; these distress flashes consist of consistent, rhythmic single flashes repeated every 1.5–3 sec [19] and are easily distinguished from firefly courtship flashes. We also looked for continuous stationary glows emitted from the light organ of injured fireflies. Whenever predatorprey interactions were observed, they were recorded and photographed (Sony Cybershot DSC-T20). Prey captured by orb-weaving spiders was monitored by counting firefly and other captured prey nightly in webs at ∼2400 h, toward the end of the P. carolinus flight period. Since webs were less likely to contain glowing prey towards the end of the firefly season, web surveys were made with spotlights. Similar observations focusing on invertebrate predators of nocturnal fireflies were also made in other areas of GSMNP. Birds and other potential diurnal predators were not covered by our surveys, as nocturnal fireflies such as P. carolinus disperse during the day to rest on or under vegetation, and thus their interactions with diurnal predators are quite difficult to observe. Similarly, it was logistically impossible to include bat predators in our field survey. 2.2. Laboratory Tests of Photuris Feeding Preferences. While most adult fireflies do not feed, some Photuris females are specialist nocturnal predators that hunt Photinus males using a combination of stalking, aerial hawking, a (...truncated)