April 2013 Featured Paper

“Firefly Flashing and Jumping Spider Predation” by Skye M. Long, Sara Lewis, Leo Jean-Louis, George Ramos, Jamie Richmond, Elizabeth M. Jakob Animal Behavior 83 (2012), pp. 81-86

Fireflies are well known for using their flashes to attract a mate. But does the flash influence predator behavior, either by alerting predators to the firefly’s presence, or by serving to warn the predator that the firefly is an unpalatable meal?

This study explores what effects the firefly flash has on predatory jumping spiders with the following questions:

  1. When attacking a firefly, are the spiders startled by their sudden flashing of light?
  2. Does the firefly’s flashing attract a spider’s attack, or deter it?
  3. Do jumping spiders learn to avoid unpalatable fireflies by their flash?

METHODS AND RESULTS

Firefly Disturbance and Flash Behavior

The researchers first had to determine if fireflies would flash during the day in a non-mating context. Both male and female fireflies were tested in the lab for daytime flashing. Fireflies were placed in a petri dish, left undisturbed for three minutes, then were tapped with a paintbrush. Left untouched, the fireflies did not flash, but were significantly more likely to flash when disturbed.

1. Testing the Startle Hypothesis

To determine whether an attacking spider is startled by a flashing light, crickets were tethered in place in a petri dish next to an LED light. Jumping spiders were then introduced into the petri dish. When a spider moved towards the cricket, the LED was turned on. The spiders showed no startle behavior when the LED was lit.

2. Effect of Flashing on Spiders’ Prey Choice

To test whether flashing lights affected the likelihood of a spider attack, spiders were given a choice between crickets tethered next to an unlit LED, a continuously lit LED, and a blinking LED. Spiders were significantly more likely to attack prey next to the blinking LED than they were to either an unlit or continuously lit LED.

3. Effects of Flashing on Avoidance of Unpalatable Prey over Multiple Encounters

Ellychnia corrusca is a firefly that is poisonous, but does not produce light. In these tests, an E. corrusca was placed in a petri dish next to an LED light, and a spider was introduced into the dish. The LED remained unlit in one set of trials, while in another, the LED flashed. Each spider was tested a total of seven times.

During the first set of trials, the spiders were just as likely to attack a firefly next to a flashing LED as they were a non-flashing LED. The spiders’ rate of attacks on fireflies with the unlit LED remained the same through all seven trials. However, by the seventh trial, no spider attacked a firefly positioned next to a flashing LED.

In each of the trials, the spider rejected E. corrusca as unpalatable and released it after the initial contact.

DISCUSSION

Test results indicated that fireflies do not flash in the daytime unless disturbed. Jumping spiders coming in contact with fireflies during the day will cause them to flash. Jumping spiders are not startled by a firefly’s sudden flash, as some predators are known to be, but instead seem more likely to attack prey that is flashing.

The spiders will attack both non-flashing and flashing fireflies even if in both cases the fireflies are toxic. In each case, the spiders will reject the captured firefly because the firefly releases chemicals through reflex bleeding that are noxious. However, after several attacks, spiders will learn to avoid attacking fireflies that flash while still attacking those that don’t flash. The spider will associate flashing with the prey’s unpalatability.

In summary, firefly flashing may initially attract a predator’s attacks on nontoxic fireflies, especially when no toxic fireflies are present. However, if toxic fireflies are present, predators will learn to avoid a flashing prey after several previous attacks on noxious fireflies. Attacks on flashing fireflies are eventually deterred, as the predator learns to connect the flashing with an unpalatable meal.

The effectiveness of the firefly’s flashing as a deterrent to predation may depend on the local firefly population—on the relative frequency of toxic and nontoxic fireflies.


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