Lighting Bugs: The Flash and the Furious

Photo "Star Trails and Fireflies, June 22, 2009" by Steve Irving, used with permission

Nothing quite expresses the sublime joy of watching fireflies paint the night sky with their glowing tails. Few realize, however, that their beautiful language is for the purpose of mating. Male fireflies take off just after dark, emitting a telegraphic pattern of flashes that can vary in intensity, shape, length, and periodicity. Each species has a unique flash pattern which the female recognizes among all the other flashes as the one belonging to her species. In between pattern repeats, the male waits for the female to respond with her own characteristic flash from her hiding spot in the vegetation. When he catches sight of her come-hither flash, the male circles back, repeating his flash pattern and waiting for her to repeat her response. This way the male and the female firefly call to each other in the dark until they locate each other and consummate their romantic conversation.

Fireflies are beetles belonging to the family Lampyridae. They spend most of their lives as larvae (glow-worms), living in dark and muddy places and preying on snails. Like moths, their adult lives are short. Like moths, many beetles related to fireflies will use sex pheromones rather than light to attract their mates. The unique bioluminescence of fireflies, however, allows them to wait until dark (when birds and other predators are asleep) to come out to mate. Specific flash patterns make the species immediately identifiable from a long distance at night. The frequency and intensity of light flashes can also communicate information about the male's quality as a mate. These advantageous aspects to light communication has led to the evolution of light-based sexual signals four times in the firefly lineage.

The flash dance of fireflies can be exploited, however. If you're skilled with a small pen-light you can trick male fireflies to land on your hand by flashing back at them as a female firefly would. Females of the genus Photuris have also learned to pull this prank on male fireflies. Photuris females will call to males of other firefly species, but not for mating. These femmes fatales are looking for a snack. The male, oblivious to the fact that the female below is not of his own species, flies straight into her welcoming jaws.

Figure of firefly flash patterns by J. E. Lloyd, University of Florida from Fireflier Companion (1998) 1(4): 56.
Image of Photuris female munching on male also by J. E. Lloyd.

What is a cockroach?

Green cockroach (Panchlora sp.?), originally uploaded by pbertner.

This is a cockroach, order Blattodea. Insects in the order Blattodea (or Blattaria if you're old-school - either way it's a roach) are characterized by long, slender cursorial (running) legs with which they achieve impressive speeds. The top of their first thoracic segment (aka the pronotum) extends up to cover their heads as a shield-shaped hat. Their mouths contain a pair of plain, sensible mandibles for chewing, their 30+ segmented antennae are thin and sensitive, ranging far ahead of their body to warn of impending danger as they run. In those cockroaches that have wings, the first pair is thickened, leathery (they're called tegmina), protecting the hind pair that is thin and membranous.

Many cockroaches are earth-toned: dull brown, tan, red, and black. A few, like the beautiful cuban cockroach (Panchlora nivea) pictured above, have striking coloration.

One thing a cockroach is not, however, is fancy. You will never find them trying to stand out with flashy patterns. They are meant to blend in with the background. Flat bodies, shielded heads, leathery forewings, the body of a cockroach is made for sneaking into small hiding places and for furtive avoidance of malicious predators. Their beauty is a functional one.

Limits of adaptationism

Yesterday we talked about the "why" of insect antennae. Why ask why?

When biologists ask "why" - they are usually asking for a functional "because." The question could be re-phrased as "what for?" This is a very old approach for understanding how biological things work. It assumes that there's a certain order to things, that organisms are a certain way for a reason. God, in his infinite wisdom, made them that way to be suited to their world.

William Paley talks a lot about this. He's the guy who came up with the watchmaker argument for the existence of God. This argument basically states that a watch is complex and contains a mechanism that works in a intricate way to keep time, so when we see a watch, we get a sense that it has purpose and design and therefore a designer. Living things like animals and plants are likewise complex and work in an intricate way to perform their tasks of survival and reproduction. Ergo, living things have design and have a designer. And it follows that the traits expressed by these living things should have a purpose in that design.

But what about traits of living things that seem to have no function? Are they just fanciful inventions of a whimsical God? Whimsy is not something I typically attribute to God. So perhaps there are other explanations. For the next several days we'll examine the limits of adaptationism - why we cannot always ask why and get a straight answer in biology.

Antennation

Insect antennae are sophisticated organs that can perform many functions for insects:

• Olfaction (smell)
• Gustation (taste)
• Mechanoreception (feeling)
• Hygroreception (humidity detection)
• Thermoreception (temperature)

Basically, antennae can do everything but see. They play powerfully in orientation of the insect in space; detecting wind speed and direction, the smell of pheromones in the air leading them to a mate, or the subtle vibration of prey below the bark of a tree. What is interesting to me is that antennae have so many different forms. Termites have simple moniliform antennae like tiny strings of tiny beads. Silkmoth and mosquito males have elaborate bipectinate plumose antennae. My small hive beetles have adorable club-shaped antennae which make them look like Mickey Mouse when they hold their antennae up. The antennae of house flies are two fat dangly bulbs with a single feather mounted at the top of each. The antennae of scarab beetles terminate in a fan-like array of delicate fingers called lamellae that can be spread open or closed tightly like a fist and tucked away into cavities under the insect's head. Dragonflies have nothing but two short bristles for antennae. Dizzying variety is the rule when it comes to antennal form. So why so many types? Does each of them correspond to some special life-style like insect leg types?


Question of the day:

Why are there so many types of insect antennae?

Answer:

Dunno.

No, seriously- we don't know why there are so many types of insect antennae. Generally, where olfaction is important, we find more elaborate or specialized antennae, such as those of male moths. Dragonflies, on the other hand, hunt primarily by sight, and thus may be forgiven for having simple and uninteresting antennae. Evolution seems to have favored divergence in most cases and convergence in a few like the elbowed antennae of weevils and ants. Beyond that, antennae are as diverse as the insects themselves. Family resemblance in the antennae is quite useful for classifying insects, but why scarab beetles have fancy lamellate fingers and small hive beetles small club-shaped antennae is rather a mystery.

Some questions in biology will always be easier to answer with "It's for decoration" or "Because that's how God made him." And perhaps in a sense, this is true- that God has seen fit to elevate diversity over uniformity, and style sometimes seems to trump function. But as we scientists study and search for a function for strange traits and find that they do, indeed, have a function, are we disappointed? On the contrary, when fascinating form and amazing function come together we get a new sort of joy- beyond the joy of beauty and the joy of a well-made machine. It is the joy of something that is, on all accounts, very good - just as the creator said it was.