Insects are a helpful bunch

By Kim Pullen – Australian National Insect Collection

The vast majority of insects may not affect us in ways we observe directly, but each plays a role as a component of our functioning environment.

They help regulate plant and animal populations and recycle organic matter in all its forms. They are crucial in plant pollination and seed distribution, and are themselves food for birds, mammals, reptiles, fish and invertebrates, including other insects.

In Australia the indigenous population have long known about the benefits of readily available ‘bush tucker’ provided by insects as a food source that can be collected in the wild.

Some insects are sought out being a protein-rich food, such as the Bogong moth (Agrotis infusa) and Witjuti grubs (larvae of certain moths and beetles), while others are sought for their sweetness, such as Lerp insects (Psyllidae), Honeypot ants (Camponotus inflatus) and native Stingless bees.

Honeypot ants hanging from the roof of a nest chamber (Image Densey Clyne)

Most honey is now a product of introduced Honey bees (Apis mellifera) brought here in the early 1800s. City-living Australians almost never eat insects, but in tropical parts squashed Green tree ants mixed in water can make an interesting tangy drink.

Spiders and other arachnids produce silk, as do many insects. These silks have astonishing properties of strength for their weight and the race is on to find a way to synthesize the best of them. Silkworms (Bombyx mori) have been domesticated for thousands of years as the source of the raw material for the luxurious cloth.

Artificial bee silk

Predators and parasites are good at finding their prey and hosts – their survival depends on it. In our own gardens and crops, these beneficial insects are busy attacking pests, as long as we take care not to eliminate the good ones by spraying for the bad ones.

Caterpillars of the Prickly pear moth (Cactoblastis cactorum) hollow out the plant, causing it to collapse

Where a harmful insect or an unwanted plant is getting out of hand because its natural enemies are missing, we can import those enemies to deal with it. In the Queensland towns of Boonarga and Dalby there are monuments in honour of the Prickly pear moth  (Cactoblastis cactorum).

The surrounding country was overrun by the cactus until the moths, introduced from Argentina, decimated it in a few short years after their liberation in 1925. The dramatic job put biological control on the map.

I’m an insect and I’ll eat you!

By Kim Pullen – Australian National Insect Collection

Often when we see insects, their feeding is what has brought them to our attention. Weevils in the pantry, silverfish in the library. Caterpillars eating the tomatoes. Ladybirds doing a good job on those aphids. Mosquitoes tormenting us at the garden party.

Insects, like all organisms, need energy to live and function, and they get that energy from food. One way to make sense of the myriad of food habits animals have is to divide them into three groups: carnivores, that eat animals; herbivores, that eat plants, and fungivores, that consume fungi.

Although the typical image of a carnivore is that of a ferocious predator, this is only one way to get a ‘meat’ meal.

A Mantis’s keen eyes, trap-like legs and lightening reflexes mean a quick death for unsuspecting prey. (Image Paul Zborowski)

A predator kills its prey, but then it has to go looking for more, which can use a lot of energy. Why not simply attach yourself to another animal, or get inside and feed off its fluids?

This Robbefly has caught a Cicada bigger than itself, and is busy sucking out its juices. (Image E.Zillmann)

Food when you want it, for less work. This is parasitism, a second kind of carnivory. Parasites feed off another animal (the ‘host’) without killing it – although the parasite may transmit a third, more deadly organism, such as when a mosquito transmits malaria, another parasite.

Some groups of insects fall somewhere between predator and parasite in their way of feeding. They are like parasites, but eventually kill their host, literally eating it alive until nothing is left.

A parsitoid wasp inserts an egg into an aphid

Many wasps follow this pattern, and they are termed parasitoids. The mother wasp searches out a luckless host and may paralyse it with a sting. In some cases the paralysis is permanent, and the wasp drags the prey to its nest, lays an egg on it, and seals the nest.The egg hatches into a maggot which consumes the host over a period of weeks or months, eventually emerging from the nest as a new adult.

In other cases the wasp simply inserts an egg in the host and leaves. The hatching maggot consumes the insides of its poor host, taking care not to eat any essential organs until last!

We’re insects and we’re everywhere

By Kim Pullen – Australian National Insect Collection

September is Biodiversity Month, and there is no more diverse class of animals than insects.

Of the 1.18 million species of animals that have been given scientific names – or ‘described’, in the parlance of taxonomists – fully one million (85%) are insects. Yet this is only a fraction of what we think really exists.

Most animal biodiversity consists of insects. These moths (and a few bugs) were attracted to a light

Taxonomists have been describing new species since Carl Linnaeus devised a workable system 250 years ago. Linnaeus and his European colleagues began with familiar animals and plants in their surroundings, expanding into new realms as microscope technology revealed strange new forms of life, and explorers brought back exciting specimens from newly penetrated regions.

Workers competed to get authorship of large and spectacular species. Unfortunately for their documentation, the majority of insects don’t figure high on the scale of large and spectacular, so that even now, perhaps 80% (and by one estimate, 98%) have not been given names. And given how new kinds keep turning up, we can assume many have not even been discovered yet.

How did the phenomenal diversity of insects come about? To start with, they originated on this planet a long time ago in geological terms, so they have had ample opportunity to diversify and exploit other organisms also evolving, such as flowering plants. (Of course, they have also had plenty of time to go extinct, too. The fossil record shows us that whole groups have disappeared entirely.)

Insects have been able to exploit the sustained burst of evolution that has produced flowering plants. This is an Emperor Gum Moth caterpillar.

Other suggested factors in insects’ favour include their short generation time, sophisticated sensory and nervous systems, ability to fly and the way many change form, or metamorphose, during their life.

Facilitating some of these factors is the small physical size of insects. Few habitats on land and in fresh water have not been taken up by some form of insect. A single tree in a woodland or forest can play host to hundreds of species, each exploiting its own niche. They will attack the roots, wood, bark, leaves, flowers, fruit and seed from the inside and outside. These herbivores will in turn be eaten by other creatures, many of them also insects. As Jonathan Swift observed, “a flea hath smaller fleas that on him prey”.

The small size of insects lets them occupy numerous small ecological niches. Here, a tiny paracitic wasp is laying an egg inside an aphid.

The upshot is that, if you were to pick a name at random from a list of all the animals in the world, there is a 4 in 5 chance it would be an insect.