It’s got 6 legs but it’s not an insect!

Q. When is an animal with six legs not an insect? A. When it’s an entognathous hexapod.

Until fairly recently it was thought that all animals with six legs were insects. It is now widely accepted that there are two classes of six-legged animals – the insects (class Insecta) and the entognathous hexapods (class Entognatha).

The Entognatha are six-legged animals characterized by mouthparts which are hidden away in a pouch in their head (entognathous). The insects (Insecta) have mouthparts which are not hidden (ectognathous).

HEXAPOD Noun. (Greek, hex = six + pous = foot.) Any 6-legged arthropod.
ENTOGNATHOUS Adj. (Greek, entos = within, inner + gnathos = jaw + Latin, –osus = with property of.) Hexapods with mouthparts recessed within head.
ECTOGNATHOUS Adj. (Greek, ektos = outside + gnathos = jaw + Latin, –osus = with property of.) An organism with protruding mouthparts.

The class Entognatha contains three orders: Collembola (springtails), Protura and Diplura. As well as recessed mouthparts these three orders have a few other things in common. They are all wingless (apterous). Also there is no visible change in form between the life cycle stages other than in size, meaning they don’t go through a process of metamorphosis and so are termed ‘ametabolous’.

The largest of these orders is Collembola, the springtails. There may be as many as 2000 species in Australia, many of them undescribed. They are called springtails because they have a prong at the tip of their abdomen (known as a furca) that is folded back like a spring. When released, the individual is launched into the air. You can see the furca in the image below. Springtails are usually tiny animals about 1mm to 3 mm long.

Collembola

Almost all springtails are considered beneficial species because they contribute to the breakdown of organic matter. There is one pest species in Australia and that is the so-called lucerne flea (Sminthuris viridis) which may damage emerging seedlings. Springtails don’t have eyes as such, instead they have a cluster of light sensing organs (known as ocelli) on each side of the head. You can see ocelli on the side of the head of the super cute springtail in the image below.

Springtail

Protura are rarely seen, tiny (< 2 mm long), pale, hexapods which may occur in soil, leaf litter, decaying wood and moss. There are about 30 described species in Australia. They have no eyes or antennae and hold their front legs forward apparently to feel their way around. Proturans were not described until 1907 and to this day very little is known about their behaviour. Some species have been observed feeding on mycorrhizal fungi, but it remains to be seen if all Proturans feed exclusively on mycorrhizal fungi. The line drawing below comes from CSIRO.

Protura

There are 31 described species in the order Diplura which occur in Australia. They vary greatly in form and size from pale delicate hexapods less than 5 mm in length to robust earwig-like species which may reach 50 mm in length. Diplurans have no eyes but do have a pair of antennae. They also have a pair of abdominal appendages known as cerci which are filamentous in the families Campodeidae and Projapygidae, but pincer-like in the families Japygidae, Heterojapygidae and Parajapygidae.

Diplurans of the families Campodeidae and Parajapygidae appear to be herbivorous, Projapygidae may be omnivorous, while the rest appear to be carnivorous. Heterojapyx (picture below) is certainly carnivorous. It waits buried in soil with only its pincers (forceps) above the surface, ready to grab any unsuspecting prey wandering by. Superficially it may resemble an earwig, but the lack of eyes and wings gives it away. I had never seen one of these in the flesh until recently when I stumbled upon one while chopping wood on my property. What a find!

Heterojapyx

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The Rain Moths are back!

I see them every year and they never fail to intrigue and excite me. We have several species of moths in the family Hepialidae which visit our property, but by far the most numerous and most spectacular is the species Trictena atripalpis.

Trictena atripalpis

They usually all emerge on the same night and are drawn to our house lights, as you can see above.They need to emerge together because they only live for one night, so they must find a mate and the females must lay their eggs on the night. The trigger for their emergence is heavy rain, and we had quite a dump last night, about 40 mm or so.

In the morning there were only a few survivors left. During the night they were systematically picked off by owls and bats, and in the morning the day birds got the rest. I was only able to find two surviving moths around the house in the morning. The image below shows one of them. It should give you a pretty good idea of their size!

Trctena atripalpis

These moths emerge from underground, because their larvae are root feeders, leaving a pupal skin poking out of the ground. Sometimes just the tip of the skin is poking out of the ground, like in the image below, but on other occasions the entire skin is accidentally hauled out onto the surface.

pupal skin

If you are interested in learning more about these moths you can read one of my earlier posts entitled “Night of the Ghosts“. There is also a page on these moths in “Backyard Insects“.

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Preying on a mantis

For every insect out there, there is another insect which will try to eat it or breed in or on it.

Praying mantids are common predatory insects found in virtually any part of Australia in any habitat where they can find prey. Mantids are an insect Order all of their own known as Mantodea, comprising about 2,500 species worldwide, and about 200 Australian species. These insects are commonly called ‘mantises’ or singularly as a ‘mantis’ – but they are more correctly known as ‘mantids’ or singularly as a ‘mantid’.

Mantids are instantly recognisable insects with their triangular heads and their characteristic way of standing with forelegs held together as if they were praying – hence ‘praying’ mantid (image below). The word ‘mantis’ is derived from the Greek word for ‘seer’ or ‘prophet’, which probably alludes to their praying stance. There is a genus of mantids bearing the name Mantis – for example the classic ‘praying mantis’ Mantis religiosa found through Europe, Asia and Africa. Australia only has one representative of that genus, a mantid known as Mantis octospilota.

Praying mantid

Mantids can be found from treetops to ground level usually widely dispersed and solitary. They are non-specific predators and will prey upon a wide range of other insects, and some large species have been observed feeding on frogs and small lizards. Mantids will attack and eat their own kind – which is probably why they are mostly solitary! Female mantids are known to eat males after, and sometimes during, mating. Serious entomological texts maintain that this activity is usually observed under caged conditions and rarely in the wild. Courtship usually doesn’t precede mating; males just tend to leap onto the backs of females at opportune moments.

The triangular heads of mantids are very mobile and they have large eyes, which must help enormously when spotting prey . Mantid forelegs are armed with rows of spines (described taxonomically as ‘raptorial’). When prey is within reach, the forelegs are shot forward and the victim is impaled and held tight with the spines, and then lifted up to the mantids mouth parts and eaten alive.

Some species sway from side to side while slowly stalking prey – possibly mimicking a twig swaying in the wind. Interestingly other insects such as certain species of katydids also sway like leaves in the wind, not to stalk prey but as protection from predators. Most mantid species rely on cryptic colouring as camouflage and sit motionless, waiting for prey to come to them. The bark mantid Gyromantis sp. (image below) is a classic example.

Praying mantis

Males of most species have two pairs of wings, both of which are used in flight, while females of most Australian species have either reduced wings or no wings at all.  A males of a large species in flight is a sight to behold. The forewings of winged species are hardened to protect the more delicate hind (flight) wings. Mantid species vary in size from about 10 mm to a massive 120 mm in body length. Common species such as the garden mantid Orthodera ministralis (image below) are about 40 to 50 mm in length.

Praying mantis

Mantid eggs are laid in moist frothy liquid which hardens into an egg case (ootheca). Egg cases and are commonly found on fences and tree branches, and may contain hundreds of eggs. The size and shape of the egg case, and the number of eggs within, varies from one species to another. The eggs hatch into nymphs (essentially miniature versions of their parents without wings) which immediately hunt for and feed on small, soft bodies insects. The eggs of mantids are often parasitised by parasitic wasps and flies, and eaten by predatory insects such as ants, as well as by small mammals and birds.

I kept a mantid egg case in a container to see what would hatch out. About 100 mantid nymphs emerged along with 50 or so parasitic wasps (Podagrion sp.), which lay their eggs in the egg cases of mantids. As you can see from the photograph here (image below) this species of female parasitic wasp has a long ovipositor, but she must insert it in a mantid egg case before it hardens. To achieve this she either follows the mantid female or hitches a ride (a behaviour known in zoology as phoresy). As soon as the mantid egg case is complete, she inserts her eggs inside. The wasp eggs hatch and the emerging wasp grubs feed on the mantid eggs within the protection of the mantid egg case. In the mantid case I collected many mantids survived these clever wasps and hatched before being eaten.

Podagrion

Mantids are usually seen as being ‘good bugs’ but because mantids are usually widely dispersed they have little economic significance. Being non-specific predators they will attack beneficial insects as well as pest insects – unlike us they make no distinction between a pest fruit fly and a beneficial hover fly. However due to their low numbers they are unlikely to significantly affect populations of beneficials. My personal view is they should be seen as ‘benign’ i.e. neither good nor bad – and they are certainly interesting!

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Tomato fly – revisited

An email conversation with an entomologist from New South Wales prompted the addition of a paragraph (in bold) to this article from about a year ago.

I picked a tomato off the bush the other day and noticed a little hole in it. I cut it open and saw that the contents were looking a bit ordinary, as if it was about to rot. Under higher magnification I could see the culprits – fly larvae – yep, maggots! The image below shows a close-up of one.

tomato fly larva

Queensland fruit fly (Bactrocera tryoni) and Mediterranean fruit fly (Ceratitis capitata) are known to lay their eggs in tomatoes, but neither of these species is found in my region of Victoria. The larvae of vinegar fly (Drosophila melanogaster) – known in America as “fruit fly” – feed in fallen rotting fruit, but this tomato was on the plant. So what species of fly produced the larvae?

I put the offending tomato in a plastic container and waited. Over a few days the larvae grew bigger, allowing me to take the photograph above, and started to jump around the container. I knew this was a sign the larvae didn’t want to be in the moist tomato pulp anymore, and were looking for somewhere dry to pupate. I shepherded as many jumping larvae as I could into a dry container with some tissue paper at the bottom, and by the following day they were all pupae.

The flies haven’t emerged yet, but I know what species they are because I went through this same exercise last year. Behold, the metallic-green tomato fly Lamprolonchaea brouniana (Diptera: Lonchaeidae).

metallic green tomato fly

These little flies are only about 4mm long, so they might be a bit hard to see in the garden. The good news is that, in my garden anyway, they are not in very large numbers and don’t lay eggs in every tomato. It is an endemic species that has been most commonly collected from the temperate south. Those wanting to learn more about this pretty little fly could jump onto the Australian Fauna Directory here.

(Note – The “jumping” behaviour of the larvae of these flies is not unique. Queensland fruit fly larvae also “jump” when they leave the larval substrate to pupate. My NSW correspondent suggested that this has led to some confusion in Victoria where people are assuming these metallic-green tomato fly larvae are Queensland fruit fly larvae. Then they wonder why their Queensland fruit fly traps and baits, which are specific to QFF, aren’t working. This illustrates why accurate identification is vital in pest management.)

One more thing about the vinegar flies mentioned above. Don’t be alarmed if you find lots of little flies in your compost. Vinegar fly larvae help with the decomposition process. You don’t need to “get rid of them”! Vinegar flies are about 3.5 mm long and look like this (below).

drosophila

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What’s good about ants? Plenty.

Many people, especially gardeners, only see ants as pests, but they couldn’t be further from the truth. These days I work weekends in a garden centre, and when summer arrived every second customer I encountered wanted a product to kill ants. One person even asked me for the “Agent Orange” of ant insecticides! They were somewhat bemused when I asked “What sort of ants are they, and why do you want to kill them?”

ponerine ant
This harmless ponerine ant is holding a water drop in its mandibles.

There are more than 1,300 described species of ants in Australia, but only a minority are considered to be pests. Most ant species are beneficial in some way. Ants are extremely important in the environment and are sometimes referred to as ‘ecosystem engineers’. For example, in bushland, ants are vital dispersers of seeds, a mutually beneficial practice known as myrmecochory. Many Australian plants, about 1500 species or so, have evolved to produce seeds with elaiosomes, which are expendable seed parts containing oil, protein, starch, sugar and vitamins. Ants collect the seeds, and carry them off to their nests underground. However, they only eat the elaiosomes and discard the rest of the seed in a ‘rubbish tip’ section of the nest, or hide them under leaf litter outside the nest. The seeds are then sort of planted, safe from predation or fire, where they can germinate safely.

Mind-boggle alert! Some stick insects exploit these ants’ seed-burying behaviour by laying eggs that look like seeds (see below), and even have an expendable fatty part for the ants to feed on. The eggs are collected by ants and taken into their nests where they are safe from predators. When the young stick insects (nymphs) hatch they even look and smell like ants. The nymphs then wander out of the nest, past the unsuspecting ants, and up the nearest gum tree to feed on the leaves.

Phasmid eggs

Anyway back to the ants. Ground-dwelling ants aerate the soil while digging their nests, which allows water to penetrate the soil more effectively. Those ants that make their nests in dead wood aid the decomposition process of that wood. Many ant species are predators or scavengers consuming vast numbers of the eggs, larvae and adults of insects and other invertebrates − either dead or alive. Ants in turn are food for many creatures such as birds, echidnas, reptiles and other invertebrates.

Some common ant species that are predators and scavengers include funnel ants (Aphaenogaster spp.), green tree ants (Oecophylla smaragdina), meat ants (Iridomyrmex spp.) and sugar ants (Camponotus spp. – pictured below). These ants should be encouraged and respected rather than bombed with insecticides.

camponotus

Where I live in Western Victoria there is really only one ant species to be wary of and that is the Jumping Jack ant (Myrmecia pilosula) pictured below – aka Jack jumper, hopper ant, skipper ant. Jumping Jack ant stings can cause anaphylaxis, a life-threatening condition in some people typified by constriction of the throat and difficulty in breathing. Milder symptoms include swelling and itchiness around the wound. They are extremely aggressive ants by nature and move in a characteristically jerky, jumping manner. Their movement may look a little comical, but there is nothing funny about the sting!

jack jumper ant

In a future blog post I will be writing about how some butterflies have interesting associations with certain ant species. In some cases the butterflies are totally reliant on the ants for their survival.

 

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Insect Architects

After a few months off for house painting one minute bugs is back!

I was prompted to write this post after completing an article for Hort Journal Australia on a similar topic. My argument in the Hort Journal piece was that insects are not mathematical or engineering geniuses, and that their behaviour is dictated by the instincts they have evolved with. All very scientific and anti-anthropomorphic. The post here is a bit different. Let’s marvel at the exquisite perfection of some of the structures that insects build.

Our first architects are moths of the family Psychidae – the case moths. These are harmless creatures found in most gardens throughout Australia. Cases are spun by caterpillars from silk to which twigs, sand, moss, lichen, leaves or bark are attached. The cases can open and close at each end, the front end for feeding and the rear end for ejecting droppings. I believe the species illustrated below is Lepidoscia arctiella – look at how precise those little bits of twig are!

Psychidae

Continue reading Insect Architects

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