The valuable resources that male diopsids are defending are string-thin rootlets hanging down from the banks of small streams that run through the woodland in which they live. These apparently mundane bits of straggling vegetation are the prime night-roosting sites for large numbers of females. They gather here and all face upwards, the direction from which any potential predator will come. By fighting, or at least flaunting his broad head, a male diopsid rules the roost and secures his harem.
| NAME | Jamaican fire beetle Pyrophorus noctilucus |
| LOCATION | Central and South America |
| ATTRIBUTE | brightest light production by any insect |
Several groups of insects can generate light, including the springtails, true bugs, fly larvae and especially the beetles. The well-known glow-worms and fireflies are neither worms nor flies, but beetles, and many species occur worldwide. Light-generating beetles use their lights to attract or communicate with potential mates. Some flash to a secret rhythm, while others emit a continuous pale glow. There has long been debate about which beetle species might be brightest and until recently comparisons were rather subjective, usually describing the similarity to a candle at some set distance as seen by the naked eye or to stars of various brightnesses. Supremely accurate photometers can now measure light production down to the atomic level, and a clear winner has been found – Pyrophorus noctilucus, a click beetle found in forests in the West Indies.
It is auspicious that this species should rank highest. In 1885 the French physiologist Raphael Dubois first isolated the compounds luciferin and luciferase by dissecting the glowing spots on the thorax of P. noctilucus. Similar chemicals are found in all light-emitting organisms. Light generation by living organisms (known as bioluminescence) is remarkable because it is ‘cold’. Using the old candle analogy, a firefly produces 1/80,000th of the heat that would be created by a candle of the same brightness.
The chemical reactions that produce light are based on the enzyme luciferase, which combines luciferin with oxygen and adenosine triphosphate (ATP). The significance of Dubois’s discovery was not fully understood for nearly 60 years until ATP was identified as the energy-carrying molecular currency in every living thing. In photosynthesis, light energy is captured by green plants and transformed into chemical energy in the form of ATP. This is used to make basic sugars and other substances from carbon dioxide in the atmosphere and water taken up by the roots. Photosynthesis absorbs light; bioluminescence releases light. The two reactions are equal, but the reverse of each other.
| NAME | ten-spot ladybird Adalia decempunctata |
| LOCATION | Europe |
| ATTRIBUTE | over 80 different named colour or pattern forms |
Naming plants and animals should be a relatively straightforward procedure. Since the Swedish naturalist Karl von Linné (also Latinised to Carolus Linnaeus) developed the binomial (two-name) system, each organism has been given two names. Thus, for the seven-spot ladybird we have one name for the genus, Coccinella, meaning ladybird, and one for the particular species, septempunctata, meaning seven-spotted.
Except that nothing in nature is that straightforward. The common seven-spot always has seven spots, but the closely related ten-spot ladybird, Adalia decempunctata, very rarely has ten. In fact it can have anything down to no spots. It can be red with black flecks, black with yellow shoulder marks, chequered, netted, speckled or barred. When early naturalists put Linnaeus’s binomial system into use, they went to town with ladybirds.
There was sexmaculata and sexpunctata for six-spotted ones; octopunctata had eight spots, quadripunctata four; semicruciata was halfway to having a cross on its back; semifasciata had half a stripe; centromaculata had spots down the middle; triangularis had three marks; subpunctata had small spots; obscura was obscurely marked. There was only one small problem – all these were the same species.
There are over 80 different named forms of the ten-spot ladybird, many once thought to be separate species, but now recognised as one species featuring different genetically controlled colour patterns. Geneticists are still trying to work out how these patterns are controlled at the level of the genes and the DNA.
These are not races or subspecies, where particular colour-ways occur in discrete geographical zones or different places around the world. The different patterns often occur together, and in breeding experiments many different patterns can appear in the offspring of identical ‘normal’ ten-spotted parents.
One selection pressure that can drive the evolution of a diversity of forms is the presence of predators that hunt by favouring one precise colour-way. Birds, in particular, hunt using a ‘search-image’ in their brains, seeing targets that match the image but missing others that look slightly different. By having many different patterns, at least some individuals should survive to reproduce. The only trouble with this theory in this case is that all ladybirds are brightly coloured to remind birds not to eat any of them because they taste horrid. Quite why the ten-spot ladybird should have such versatile patterns is still open to debate.
| NAME | bloody-nosed beetle Timarcha tenebricosa |
| LOCATION | Europe and Central Asia |
| ABILITY | deliberately spits out its own blood |
Insects defend themselves from attack in many different ways. After hiding, possessing a weapon is one of the commonest strategies. The weapon may be biting or stinging an enemy, but it may also be simply tasting foul. Plenty of plants contain noxious chemicals to deter herbivores, and plant-feeding insects can take advantage of this fact by storing the poisons in their bodies.
There is one drawback for the individual with the poisonous body. Although birds (the main insect predators) may soon learn to avoid a particular species because it tastes disgusting, that is a bit late for the individual insect they have picked up, crushed, chewed and swallowed, even if they then vomit it back up again. It would be much better if the insect could warn of fits potential predator by giving it a taste of what might come should the meal be fully consumed.
This is exactly what many beetles do. Rather than wait until their innards are squashed out in the bird’s beak, they defensively squeeze out large droplets of their foul-tasting haemolymph (blood). As soon as the bird tastes the bitter chemicals, it spits out the not-so-tasty morsel more or less unharmed.
The commonest beetles to use this defence, called reflex bleeding, are ladybirds, which exude droplets of their yellow body fluids from special pores in their knee joints. The most spectacular, though, is the aptly named bloody-nosed