Visual Communication
In the context of orientation, vision is extremely important to most insects, as it is to most animals
in general. However, for communication, insects tend to rely more heavily upon their other sensory
systems. Ethologists have found that at least two important signaling phenomena are more readily
studied in visual signals than in auditory or chemical signals. One is the origin of signaling
structures; the other is the evolutionary transformation of signals from their original purpose to
assume new roles, a process known as ritualization.
Bioluminescence
Larvae and larviform adult females of Phrixothrix beetles are sometimes called ‘railroad worms’
because, like twin lanterns, luminescent organs of their body glow green while those on their head
glow red. The predatory larvae of some small dipterans called fungus gnats are unique among flies
in producing their own light.
For centuries scientific investigators and curious lay observers alike have been fascinated by the
production of light by living organisms, or bioluminescence.
Bioluminescence occurs widely in vertebrates, invertebrates, bacteria and fungi. Ninety percent of
deep-sea marine life is estimated to produce bioluminescence in one form or another. Even
symbiotic organisms carried within larger organisms are also known to bioluminesce. Among the
Insecta, self-luminescent species occur at least nine families in five orders: Collembola,
Hemiptera, Diptera, Dictyoptera, and Coleoptera. The intensity of luminescence varies greatly
from one insect species to another. In some species, it is so low as to be visible to human beings
only by the completely dark-adapted eye.
Bioluminescence has been described in more beetles than any other group. Fireflies, lightning
bugs, or blinkies—adult lampyrid and elaterid beetles—are the most well-known probably because
there are over 2,000 species and many are widely distributed.
How is the light actually produced? In 1885 the French physiologist Raphael Dubois
experimented and showed that two substances were required for the light. These were named
luciferin and luciferase, both after Lucifer, the bearer of light.
In the presence of oxygen, the luciferase, and the cellular energy source ATP (adenosine
triphosphate), luceriferin oxidizes to oxyluceriferin, an unstable compound that is in such an
excited state it yields a photon of visible light.
Bioluminescence as a Communication Method
Why do railroad worms have red and green lanterns? Do fungus gnats in the family Keroplatidae
use their light to lure potential prey? When fireflies sometimes blink in unison, what do they
accomplish?
Bioluminescence serves many purposes in the animal world in general, and among insect species
in particular, and its functions are often different for various life stages. For immature fireflies, for
example, bioluminescence appears to be a warning signal to predators, because many firefly larvae
contain chemicals that are distasteful or toxic.
For most adult fireflies, the production of light is used to locate other individuals of the same
species for reproduction. Courtship typically takes the following sequence: Males initiate flashing
during flight at species characteristic times (often around sunset) in a well-defined habitat area;
their flight paths are also species characteristic, especially during moments of light emission.
Females remain stationary and, upon perceiving a male flash, answer with their own flashes, which
follow that of the male after a brief, again species-characteristic delay. Repeated flash–answer