Insects: a fascinating life form.

Caelifera Grasshopper that is exceptionally yellow. 

Insects make up about 90% of all known animals. One million species have been described and this number is estimated to be between 10 and 20 percent of the total amount of insect species in existence (there are still a lot to be discovered). A testament to the biological success of insects is the time they have been around. The first insects are thought to have emerged during the Devonian period about 420 million years ago.

Insects are great consumers of plant matter and play a far more important role as primary consumers than mammalian herbivores. That means that they introduce a large amount of carbohydrate energy into the nutrient cycle that they acquire from plants.

Insects are not only important consumers, they are also important decomposers and are responsible for breaking down large amounts of dead organic matter and returning those nutrients back into the nutrient cycle.

Crematogaster ants consuming the soft insides of Beetle.

Insects are food for many animals. The insect eating suborder of bats, Microchiroptera, has one of the highest species diversity amongst mammals. There are about 830 species of Microchiroptera worldwide. [1] This species diversity would not be possible without insects.

Birds migrate in order to take advantage of insect population explosions. The Amur Falcon can migrate over 14 000 kilometers from Russia and Northern China to take advantage of termite alates and grasshoppers in Southern Africa. [2] 

Spiders are great consumers of insects. Araneomorphae, which are spiders that build webs in which to catch their prey are the primary insect eaters. Studies have estimated that spiders can consume up to 200 kilograms of insects per hectare per year. [3]

Nephilia eating a Locust.

Besides just being food, insects also play a major role in pollination and many plants have evolved with a specific insect and each is reliant on the other for each other’s existence. The best example of this relationship is that of the fig wasp and it’s specific tree of the Ficus genus. In general, every species of fig tree has a unique species of wasp that pollinates the fruit and allows the fig to reproduce. This mutualism is a good example of coevolution.   

The lifecycles of insects is another fascinating aspect of insect biology. There are two basic types of insect lifecycles: the hemimetabolic (incomplete metamorphosis) and holometabolic (complete metamorphosis). Grasshoppers, dragonflies and termites are examples of the first; moths and butterflies are examples of the second. In insects with a holometabolic lifecycle, the larva can be viewed as the feeding stage and the ‘adult’ can be seen as the breeding stage. The term adult is in fact misleading: and the more specific term imago is preferable. [4]

Chrysomeloidea Leaf Beetles mating.

In the same vein as seeing the larva as the feeding stage, one can take the thought further and it doesn’t take much imagination to see the larva as the mouth and the ‘adult’ the reproductive system of the insect which is no longer a unitary organism; rather the species takes the place of an individual. This way of looking at insects makes them bigger than the traditional way of seeing the puny ant walking in the great wide world. It’s a complicated idea and not very well expressed, but something to think about.[5]

These Pyrgomorphidae Grasshoppers have just hatched. The nymphs instinctively congregate and cluster together. They will stick together throughout the nymph stage although groups will disperse from this black mass.

These facts may or may not be interesting to you, but what I find the most interesting about insects is their ways of living. Their insect drives to consume, congregate, swarm, stridulate, amongst other things, are the most intriguing for me. What force pulls cicadas out of the ground in numbers to climb up tree trunks and moult? What is the force that drives a katydid to perch on a plant stalk in the dark and stridulate incessantly? What is the allure of artificial light to nocturnal insects? 

Processionary Caterpillars, Thaumetopoeinae. These insects stick close together throughout the larval stage.

They then make a train of insects and move across the ground in search of other Processionary Caterpillars.

Other Processionary Caterpillars are located by the thread left by the last one in the line. The lines link up forming incredibly long lines of Caterpillars that eventually head up a tree to make their cocoons. 

Matabele Ants, Pachycondyla analis on their way out on a raid. These ants are destroyers of termite colonies. These ants stridulate when provoked.

Moribund Termite mound, the death of this colony could be attributed to Matebele Ants.

The easy answers to these questions of course are the usual deterministic answers: ‘the need to find a mate’ or ‘the need to feel secure in numbers’ or ‘the need to obtain food’.  These answers may be correct but they are looking at the surface reasons behind the behaviours. I find it far more stimulating to think about the mysterious drives hidden in the chemical make-up of these little animals. The answers to these can only be guessed at, as we will never know what it is that drives insects. This is largely because insect life is so alien to us. One just has to look at the physical appearance of insects that has come about due to their lifestyles to appreciate just how strange they appear to be.

Ants of the Polyrhachis schistacea species tending Membracid Tree Hoppers. The bugs secrete a goo that the ants relish. In this mutualistic relationship the ants gain food and the tree hoppers gain protection. The ants tend the tree hoppers in a way that is akin to agriculture.

But it is this unknown and unfamiliar aspect of insect life that drives my curiosity and interest in these small animals. The more I learn, the more I see and the more enjoyment I get out of observing these creatures.

Stone grasshopper Trachypetrella perfectly resembles the granite on which it lives.

This Stinkbug, Pseudatelus mimics fungus that grows in rotting wood.

Mimicry is another fascinating phenomenon that is prominent in insects. For me the most arresting thing about mimicry is the time it takes for natural selection to arrive at something so incredible and that is compounded by the abundance of mimicry in nature.

Katydid Zabalius aridus, resembles a leaf.

The same Katydid taking evasive action with an example of flash colouration

Net-winged beetle of the Lycus genus uses aposmatic colouration to deter predation. These warning colours suggest the beetle is poisonous or foul tasting.

Cabbage tree emperor moth caterpillars, Bunaea alcinoe, are big and conspicuous. This is another example of aposmatic colouration and the red on the face look like the development of eye spots.

This incredible animal is a Monkey moth caterpillar, Eupterotidae. They are slow moving and move over the ground. Is this a possible scat mimic?

Rhanidophora cinctigutta is a caterpillar with strange club shaped protuberances on it's body, these move in rapid and urgent gestures, the aposmatic colouration and the movement all suggest that this insect is a wasp mimic.

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[1] http://data.iucn.org/dbtw-wpd/html/SSC-Microciropteranbats/Chapter%201.html

[2] http://www.africanraptors.org/amur-falcon-migration-route-finally-plotted/

[3] http://www.conservation.unibas.ch/team/nyffeler/pdf/nyffeler2000bas.pdf

[4] For a more detailed and interesting overview of the nature of language and interpretation of the insect lifecycle see the essay by Stephen Jay Gould, Glow, Big Glowworm. Gould. 1991. Bully for Brontosaurus: Reflections in Natural History. W.W Norton & Company: New York.

[5] The pioneer of this way of thinking was Eugene Marais and these ideas were expressed in his work Soul of the White Ant which was published in 1937. This is a now outdated, yet beautiful text on the lifecycle of termites.