Monday, 26 November 2007

#39 Where are they hiding?

Insects are consumed in vast numbers every day by birds, mammals, reptiles, and other insects and invertebrates. To avoid becoming part of the food chain for long enough to develop and reproduce, an insect must be able to carry out its life with a certain degree of 'invisibility'. Just as humans employ methods of camouflage in warfare, many insects have evolved to blend into their surroundings in an attempt to hunt and remain undetected by prey.

Who is hidden, whilst in the open, amongst the leaf litter?

Here's the answer - the 20mm flightless nymph Gumleaf Grasshopper, Goniaea australasiae, blends in perfectly with its eucalypt leaf-litter habitat

Grasshoppers metamorphose gradually, moulting several times before their wings are fully developed. If the nymph is to survive to adulthood and reproduce, it must remain undetected by numerous preying invertebrates and vetebrates while feeding and growing.

Various methods of camouflage

Camouflage is a survival strategy practiced by both predators and prey. Insects are experts at camouflage, and I never cease to be amazed by the impressive disguises that I discover in the insect world.

Colour, shape, texture and patternation are the most obvious means of disappearing into the surrounding environment. An insect that mimics the colour and form of its substrate can often only be detected through the closest scrutiny.

The Gumleaf Grasshopper camouflaged in the first picture is a perfect example of an insect evolving to resemble the colour and structure of components of its immediate surroundings to avoid detection. But a grasshopper nymph that lives in tussocks of grass must take a different form.....

Can you find the 40mm flightless grasshopper nymph that extends from the top of this picture to below the centre?

Here it is, but it's even well camouflaged at close inspection, appearing just like a stick. Notice how the hind legs project at an angle giving the impression of further twigs.

As well as using colour and structure to blend into their surroundings, many insects go one step further by adopting behaviour that also mimics the movement around them. For example, stick insects and mantids will often move in a rocking motion when detected, to resemble a leaf or twig blowing in the gentle breeze. If you've encountered these creatures, you will be aware of this impressive display of deceipt.

Insects depending on camouflage remain motionless for long periods of time, some, like praying mantids, then striking at lightning speed when prey passes, unsuspectingly, right by the camouflaged creature. And some insects that resemble dead foliage will drop to the ground if disturbed, as if they are the real thing being dislodged from a plant.

This 50mm moth blended well into the mulch of my garden, but in its natural surroundings of leaf-litter, it would disappear almost entirely.

Some insects are flattened to look like leaves, others are elongated like twigs, and some even imitate objects like bird droppings, dead foliage, flower petals, and undesirable poisonous or nasty-tasting insect species. Some invertebrates will imitate other species in the ultimate game of deception. As some predators will only eat live insects, some invertebrates will even play dead. Ingenious methods of deceipt and camouflage employed by insects are endless.

The importance of insects

Insects suffer from an image problem: many, perhaps most people, consider insects as nasty, annoying, insignificant beasties to be squashed, sprayed or otherwise disposed of.

Regular readers of my nature blog will be aware of my fascination and respect for the flying and crawling invertebrates that make their homes in my backyard. I didn't always feel appreciation or regard for hairy spiders or scary creepy crawlies, and I am still occasionally faced with challenging (read, frightening) encounters of the bug or spider kind. But commonsense and a healthy dose of caution usually guide my actions.

"In Australia insects make up 75% of the known species of animals with the majority of these unique to Australia. Despite this diversity and abundance, many species are known only from a name and a specimen. Our lack of knowledge about insect habitats and ecology is a major barrier to their conservation. Without this knowledge we are unaware if species are threatened with extinction from habitat destruction or other threatening processes. Many insect species may already have been lost without us becoming aware that they existed at all." [ref: Australian Museum]

The stick-shape of the praying mantis provides means of camouflage amongst the twigs of a shrub

Insects out-number any other taxonomic group on Earth, and perform many important tasks. Scientists proclaim that most other life forms, like amphibians, reptiles, birds, and mammals would become extinct if insects disappeared, because of the domino effect that would occur in the food chain.

Pollination of plants and crops is a major role of insects. The vast majority of pollinators are flying insects. In many places, it is likely that the essential service of pollinators could be at risk due to habitat loss and pesticide use. Although pollination is a by-product of nectar-feeding and pollen-collecting insects, it is essential to the continued existence of many plants. It is estimated that two-thirds of all flowering plants depend on pollinating insects for this service.

Although some insects are pests to humans and their pets, stock and crops as they carry disease and consume or damage plants, pest or harmful insects are a minority.

Insects and other arthropods aerate the soil, and control insect and plant pests; they also decompose dead materials, thereby reintroducing nutrients into the soil. Burrowing invertebrates such as ants and beetles dig tunnels that provide channels for water, benefiting plants. And insects provide food for insects and other arthropods, reptiles, birds and mammals.

What are arthropods?

Joint-legged animals without backbones are called arthropods. Arthropods make up over 75% of the world's animal species, and include animals such as insects, crustaceans (eg. crabs and lobsters) and arachnids (eg. spiders and ticks). The largest group of arthropods are the insects. Other arthropods include centipedes and millipedes.

Some spiders also find it necessary to employ the art of camouflage. The Garden Wolf Spider (Lycosa godeffroyi) positions its hind legs over its abdomen to break up the round shape when it is caught out during daylight - an effective camouflage technique, don't you think?

Arthropods have a jointed body, an exoskeleton (external skeleton), and at least six jointed legs. Characteristics of arthropods, along with features which distinguish insects from other arthropods are explained in this link in an easy-to-read fashion.

A large Garden Orb Spider (Eriophora transmarina) takes advantage of decayed flowers to disguise its shape, remaining motionless, but in full view of potential predators - it looks safely camouflaged to me

And this caterpillar is not only camouflaged by its green colour and flattened form matching the leaves, its outstretched posture takes the imitation to another level (notice it even has a pointed tip)

Humans generally view insects and arachnids as pests and vermin that need to be controlled. They usually are not considered as something to be preserved. But insects play a major role in functioning ecosystems. They must be preserved because of their inherent values but also because we need them for human survival.

Insect cocoons, egg-sacs and pupae are also expertly camouflaged - but that's another story

Insects are masters of disguise and deception; if you can't run, you've got to hide. These complex methods of escaping danger and mounting surprise attacks are fascinating to observe. Insects, spiders and other invertebrates are vital components of all ecosystems. While taking care to stay out of harm's way, a little tolerance and understanding of bugs and insects will go a long way toward maintaining or increasing the health and diversity of your environment.

All these photos of camouflage examples except the Gumleaf Grasshopper were taken in my backyard, so I'm pleased to say that my garden has a healthy and diverse invertebrate population.


Esperance Blog said...

Hi Gaye, you must either be more patient than the insects you watch, or have better eyesight than an eagle to see your examples. I am very impressed and probably overlook dozens everyday, but as you say, that is what they want to happen.

I have a large shadehouse and catch a number of insects who fly into it, then hang on to get their bearings. They stand out starkly in this environment and make you realise the number that must be continually moving around. Unfortunately for them, the Willy Wagtail and other insectivorous birds have been quick to appreciate this food bonanza and I bet there are a lot of little fat chicks around because of it.

Fascinating blog Gaye, keep up the good work.


Anonymous said...

Hi Gaye,
Words almost fail me on the excellence of your narration. You have produced a yet another very interesting and fascinating account, this time of the intricacies of insect camouflage and to realise those photographs are taken in your backyard is testament to your extraordinary observation powers.

Well done Gaye, on a well written blog. I hope there are many people who access your site for there is much food for thought in the content of this entry.


Denis Wilson said...

Hi Gaye
Sorry I have been slow on the uptake on this posting.
Great "clean" photos, as usually. Well done. Loved your large Grass Hopper nymphs, especially. Great work to spot them.
Here I get huge numbers of moths, and, in the season, Tree Crickets, which are amazing, both for the length of their antennae, and for the ferocity of their mouths. They also can climb any surface, and enter any building built by mankind. But for scariness, (for me) it is the powerful fluid motion of the large centipede which gives me the willies. Fortunately I do not get many of them, but they combine the venom of a spider, fluid movement of a snake, and determination of - well, a centipede. They are the stuff of nightmares, for me.

Insects rule the world, though. They just let us think we do. For all our powerful chemicals, we are just a nuisance to them. Nothing can breed up as fast as insects (well, except for bacteria - but we don't get to see them).

You are right to point out how beautiful they often are - at least, beautiful in a design sense, if not in brightness of colour. The camouflaged eyes of your Leaf Grass Hopper is a good example.

Lovely post, and informative.


Gaye from the Hunter said...

hi folks,

I've been preoccupied, but I certainly appreciate your interest in my blog entry and your comments.

Thank you.