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DISPLAYING POSTS TAGGED: bug of the month (19)

Bug of the Month - the earthworm

Author
by Tim Blackburn
Publish date
1 June 2012
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June's Bug of the Month is certainly not a bug, but the integral role that the earthworm plays in many terrestrial ecosystems is why I've selected it this month. The famously influential Charles Darwin studied earthworms at great length. His 1881 book, The Formation of Vegetable Mould Through the Action of Worms, With Observations on Their Habits, sold more copies than On the Origin of Species. Darwin commented, "...it may be doubted if there are any other animals which have played such an important part in the history of the world as these lowly organized creatures."

Earthworms belong to the phylum Annelida which incorporates all the segmented worms, including the marine worms and the leeches. More than 3,000 species of earthworm, ranging in length from one centimetre to two metres, are found right across the planet in a diversity of habitats – including Melbourne Museum's gardens.

Earthworm An earthworm, showing its long segmented body.
Image: Tim Blackburn
Source: Museum Victoria

Earthworms inhabit moist, rich soils and emerge at night to feed on decomposing organic matter. They possess bristle-like hairs called setae which form a ring around most body segments. The setae help the worm to sense its environment and to grip the soil as the earthworm moves around. They do not have a skeleton, per se, but possess a fluid-filled body cavity (a coelom) against which their muscles contract. A swollen band towards their anterior (front) end, called a clitellum, secretes an egg-filled cocoon soon after mating.

Earthworm The bulge visible toward the anterior end of this earthworm is the result of the peristaltic (wave-like) contraction of its muscles against its hydrostatic skeleton. The swollen, orange band around the body is the clitellum.
Image: Tim Blackburn
Source: Museum Victoria
 

earthworm clitellum A close-up of the earthworm's clitellum
Image: Tim Blackburn
Source: Museum Victoria
 

Earthworms play an important role in stabilising soil structure and maintaining soil fertility. They are instrumental in the decomposition of organic matter and the associated replenishment of soil nutrients. Charles Darwin estimated that earthworms add a 5mm layer of nutrient-rich soil to English pastures each year.

Earthworms have a lower optimal body temperature than most invertebrates and prefer damp soils, since they must keep their cuticle moist to be able to respire through it. Earthworm activity will be high in Melbourne during June as temperatures plummet and evaporation decreases. I found a dense population of earthworms while digging up one of the garden beds in the Milarri Garden this week. The worms seem to be breaking down much of the leaf litter that accumulated during autumn, thereby returning nutrients to the soil.

Trees in autumn The current view of Carlton Gardens, looking out from the Millari Garden. Earthworms and soil microorganisms will break down the autumn leaves within a matter of months.
Image: Tim Blackburn
Source: Museum Victoria
 

The benefits that earthworms provide for soil are due to their burrowing habits and their methods of feeding, digestion and excretion. They swallow much of the soil and organic matter they encounter and deposit it as nutrient-rich faecal casts. The waste products and mucus secretions of the worms provide nutrients for many microorganisms, which improve soil fertility through further decomposition. Earthworms' burrowing actions also aerate and drain the soil, preventing it from becoming compacted and waterlogged.

These animals are essential components of both natural and human-dominated ecologies, and they've also influenced human history. For example, the migration and settlements of early humans were limited by the productivity and fertility of soils. The role that earthworms have played in the burial of ancient buildings over millennia was studied at length by Charles Darwin, a phenomenon which illustrates just how closely human societies are intertwined with earthworms. The world's diverse ecologies, agricultural systems and expansive cities owe much to the largely unnoticed action of earthworms below ground.

Links

Infosheet: Giant Gippsland Earthworm

Via Darwin Online: The Formation of Vegetable Mould Through the Action of Worms, With Observations on Their Habits

Hairy but not so scary

Author
by Chloe
Publish date
2 May 2012
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Chloe is a keeper with Live Exhibits at Melbourne Museum.

Who knew that within Melbourne Museum there are two rooms not considered to be in Australia?

Every year Australian Quarantine and Inspection Service (AQIS) officers confiscate thousands of objects being brought illegally into the country through the post, airports and seaports. These items include food, drugs, plants and even live animals.

King Baboon tarantula (<em>Citharischius crawshayi</em>) King Baboon tarantula (Citharischius crawshayi)
Image: Alan Henderson
Source: Museum Victoria
 

Such illegal items can pose a significant risk to Australian wildlife. Tarantulas are a long-lived spider which can produce thousands of eggs each year. If they were to become established in the wild exotic tarantulas would have the ability to decimate populations of small native animals.

In 1996 a population of Mexican Redrump tarantulas (Brachypelma vagans) was discovered in a citrus field in Florida, America. The population is believed to have stemmed from one gravid (carrying eggs) female who was released after she was no longer wanted as a pet. Over 100 individuals were found in a single survey of the 40 acre property. The Mexican Redrump tarantula is not native to Florida but has been imported for the pet trade since the 1970s. It is thought that this incidence of releasing an exotic pet has alone caused devastating effects on local fauna. With Australia's warm climate it would be easy to find ourselves in a similar situation to Florida if we didn't enforce strict quarantine measures.

Mexican Redrump tarantula (<em>Brachypelma vegans</em>) Mexican Redrump tarantula (Brachypelma vegans)
Image: Alan Henderson
Source: Museum Victoria
 

Tarantulas with their unique markings, behaviours, and basic husbandry are popular pets in Europe and America. Many species are illegally transported around the world with collectors willing to pay hundreds of dollars for specimens. In Australia there are numerous species of native tarantulas that can be kept legally as pets.

Venezuelan Sun Tiger tarantula (<em>Psalmopoeus irminia</em>) Venezuelan Sun Tiger tarantula (Psalmopoeus irminia)
Image: Alan Henderson
Source: Museum Victoria
 

Queensland whistling tarantula (<em>Selenocosmia crassipes</em>) Queensland whistling tarantula (Selenocosmia crassipes)
Image: Alan Henderson
Source: Museum Victoria
  

But what happens to the items AQIS confiscate? Many items are destroyed to protect Australia's precious ecosystem. However, some lucky spiders are spared. They get used by museums and zoos to act as educational aids.

Quarantine room enclosures off display at Melbourne Museum Quarantine room enclosures off display at Melbourne Museum
Image: Chloe Miller
Source: Museum Victoria
 

Melbourne Museum is home two quarantine rooms where we house 14 tarantulas that were confiscated by AQIS. These spiders are housed under strict conditions which meet AQIS standards. These standards include the treatment of objects leaving the rooms such as waste, water, uneaten food and other implements. These items must be double bagged, recorded and frozen at minus 20 degrees for six weeks. The quarantine room is not considered to be in Australia territory but a grey zone within Australia.

Bugs Alive! Quarantine room at Melbourne Museum Bugs Alive! Quarantine room at Melbourne Museum
Image: Chloe Miller
Source: Museum Victoria
 

One quarantine room at the museum is located within the Bugs Alive! gallery and allows visitors to see its inner workings through a glass viewing wall, while the other room is located behind the scenes.

Our display spiders are fed every fortnight on Saturdays. One of our 'behind the scenes' spiders is fed weekly on Fridays at 3pm live on the web.

Tarantula feeding live on the internet Tarantula feeding live on the internet
Image: Chloe Miller
Source: Museum Victoria
 

Currently on display via the webcam is a Brazilian Salmon Pink tarantula (Lasiodora parahybana). Brazilian Salmon Pinks are the third largest species of tarantula with a leg span reaching 25cm.

Brazilian Salmon Pink tarantula (<em>Lasiodora parahybana</em>) Brazilian Salmon Pink tarantula (Lasiodora parahybana)
Image: Alan Henderson
Source: Museum Victoria
 

Equipped with urticating (stinging) hairs to flick at predators, she only uses her fangs as a last resort. This girl is a keen feeder, often climbing up the keeper's forceps to get to its prey.

References:

Brazilian Salmon Pink fact sheet from WAZA

Brazilian Salmon Pink Birdeater from Australian Reptile Park

Mexican Redrump Tarantula fact sheet [PDF 179KB] from the University of Florida

1996 Florida Mexican redrump tarantula incident

Southern Grasstree

Author
by Brendan
Publish date
1 April 2012
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Exhibition horticulturalist Brendan Fleming is turning April's Bug of the Month post into Plant of the Month. He is one of the Live Exhibits staff that tend the plants in the Forest Gallery and Milarri Garden.

From an early age I have enjoyed bushwalking within the Grampian Ranges in western Victoria. One particular plant species found there that fascinates me is Xanthorrhoea australis, the Southern Grasstree. X. australis is the most widespread of the genus of 30 odd species and subspecies. It is found down the eastern coast of Australia.

Southern Grasstrees A spectacular display of Southern Grasstrees following a bushfire in the Grampians.
Image: Brendan Fleming
Source: Brendan Fleming
 

Its appearance is unlike any other indigenous plant. Older grasstrees have a blackened, sometimes gnarled elevated trunk, with bluish-green whorled leaves that seem to explode from the crown and drape down to skirt the stem.

The Southern Grasstree is very slow-growing. It grows approximately one to three centimetres per year, reaching a height of three metres in about 100 years. It has a shallow root system and is found in even the poorest of soils. Whilst not generally occurring in areas with less than 250mm rainfall, it does best in areas exceeding 500mm per year. Southern Grasstrees are found in the understorey of woodlands, heaths, swamps, and rocky hillsides.

Grasstree species are mostly distinguished by the shape of their leaves in cross-section. X.australis has a diamond shape, and with the leaves being softer than other species.

apex of a Southern Grasstree Close up of the apex of a Southern Grasstree in Milarri, showing a single diamond-shaped leaf in cross section.
Image: Brendan Fleming
Source: Museum Victoria

From germination it takes about seven years to reach maturity, and although sporadic flowering and fruiting can occur thereafter, X.australis generally flower following fire. It is not well understood why fire stimulates reproduction, but cutting off the leaves can also initiate flowering. Application of ethylene, which is present in smoke, has a similar effect, indicating that flowering is stimulated from a hormonal response to leaf removal.

I found an extraordinary scene following bushfires several years ago in the Grampians National Park. Thousands of flower spikes up to 3m high as far as the eye can see, even curly ones, evoking some Leunig illustration!

Grasstree flower spikes Although most flower spikes are perfectly vertical, I occasionally see odd shapes at the Grampians.
Image: Brendan Fleming
Source: Brendan Fleming

The flowers are highly scented and produce much nectar, prized by birds, mammals and insects which pollinate the flowers. Each stalk can produce up to 10,000 seeds.

Southern Grasstree flower spike Close-up of the Southern Grasstree flower spike showing individual flowers.
Image: Brendan Fleming
Source: Brendan Fleming
 

Southern Grasstrees are quite susceptible to Phytopthora cinnamomi (root rot), often being the first plants to show symptoms. Hence they are a good indicator of the presence of the disease.

Drenching Southern Grasstree roots with Phosphonate Drenching with Phosphonate is a good way to boost the Southern Grasstree's defences against the Cinnamon Fungus Phytopthora.
Image: Chloe Miller
Source: Museum Victoria

Xanthorrhoea australis is not difficult to propagate. Seed germinate readily in just a few weeks, with no pre-sowing treatment required. Just be patient though - growth is very slow. A grasstree I germinated from seed was well-established but still trunkless after 10 years, and made a handsome addition to my garden.

Grasstrees feature heavily in Indigenous culture. Uses include weapons and fire sticks from flower stalks, sweet drinks from flower nectar, and edible leaf bases.

I don't have to go to the Grampians to enjoy grasstrees. The Milarri Garden at Melbourne Museum displays these remarkable plants right in the heart of Melbourne. Exit the Forest gallery to the North terrace and meet Milarri from its western end. It really is a dramatic entrance to the Museum's Indigenous garden.

Grasstrees at the entrance to Milarri Walk Grasstrees at the entrance to Milarri Walk from the North Terrace during autumn.
Image: Brendan Fleming
Source: Museum Victoria
 

References:

Flora of Tasmania

Wrigley, J. & Fagg, M., 1983, Australian Native Plants, William Collins, Sydney, 512pp.

Bug of the month - Rainforest Mantid

Author
by Caitlin
Publish date
1 March 2012
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One of the largest insect species we keep here at Melbourne Museum is the Rainforest Mantid (Hierodula majuscula). At around 70mm in length, the adult Rainforest Mantid is not the longest mantid species in Australia, but it is certainly the most buff.

An adult female Rainforest Mantid on the hunt for prey An adult female Rainforest Mantid on the hunt for prey
Image: Alan Henderson
Source: Minibeast Wildlife
 

Its powerful raptorial forelegs are equipped with razor-sharp spines that allow the mantid to pin and immobilise live prey. A resident of north Queensland rainforests, the adult's solid green colour enables it to all but disappear amongst the foliage. A mantid on the hunt may remain perfectly still for hours, waiting for the right prey to present itself. Looming over its meal and appearing to "pray", the mantid finally strikes with lightning-fast accuracy and shows its true colours as another of nature's perfect predators.

The life of the Rainforest Mantid begins as one of up to 400 hatchlings from the ootheca – an egg case laid by the female 40-60 days prior. Often attached to the underside of a branch or leaf, the hatchlings emerge downwards and crawl over one another to clear the way. The nymphs must disperse from their brothers and sisters, as once they start eating, any prey small enough is fair game - including each other! At this stage, H. majuscula nymphs are less than 10mm long. As the nymph moults and grows, it may vary from greens to browns and reds, but is invariably green by its final moult.

Mantid nymphs hatching and moulting Mantid nymphs hatching and moulting for the first time after emerging from the ootheca.
Image: Alan Henderson
Source: Minibeast Wildlife
 

A superb hunter, the Rainforest Mantid's best weapon is its vision. Its large, compound eyes boast a wide field of vision, enhanced by its head's extraordinary range of movement. As a result, the Rainforest Mantid hunts primarily during daylight hours.

Mantid with large eyes Large eyes dominate the Rainforest Mantid's triangular, highly mobile head.
Image: Alan Henderson
Source: Minibeast Wildlife

An adult mantid is able to prey on not only a large selection of insects, but may also attack small lizards and frogs. After securing the prey with its raptorial forelegs, the mantid devours it alive. These mantids often eat the nuisance parts first, such as an insect's powerful kicking legs.

Mantid eating a cockroach Insect prey is usually consumed head-first to reduce the chances of it getting away.
Image: Alan Henderson
Source: Minibeast Wildlife

The Rainforest Mantid lives a solitary life and may never come into contact with another of its species after hatching until it is time to breed. Only the mature male of this species is capable of flight, so it is left to him to navigate the precarious expanse of tropical rainforest to find the perfect a female who is ready to mate. In contrast to hunting, night seems to be the preferred time for mating (though it may begin during or continue into daylight hours). As a flying male is quite vulnerable, it is thought that breeding takes place in the dark to reduce the risk of aerial predators.

However, there is still one major group of insect predators active at this time – the microbats. To combat this, many mantid species including H. majuscula have evolved a single ear on the lower side of the thorax, capable of picking up the ultrasonic sound frequencies of the microbats' echolocation signals. If the male mantid in flight detects such a signal, he immediately dives and weaves in such a display of evasive manoeuvres that he has been compared to a fighter jet.

In the dark, mantid eyes are much less effective. To counter this, a female of the breeding inclination sends out pheromones to attract suitable males. Once the male locates a female, he tempers his approach until the correct moment. He may wait hours within thirty centimetres of her, before rushing her in a mad frenzy and attaching himself to her back with his forelegs. If he is lucky, he will have attached himself a way that prevents her turning around to eat him. If he is unlucky, he may immediately become a meal. Either way, the Rainforest Mantid male can continue to mate even with his head completely missing. It's not all bad news for the male's genes: by becoming an extra meal, he may give his offspring a greater chance of survival by nourishing the female through the month of egg incubation.

Mantids mating This male is one of the unlucky individuals that has not survived the mating process.
Image: Alan Henderson
Source: Minibeast Wildlife
 

Rainforest Mantid females may live for up to a year. Though males may be capable of living just as long, their risky lifestyle results in a lower average life span. However, if a male survives mating, he may go on to mate with many more females and live to a ripe old age.

Bug of the Month: Red-back Spider

Author
by Tim Blackburn
Publish date
1 February 2012
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The Red-back Spider, Latrodectus hasselti, is a type of widow spider. It is closely related to the Black Widow (L. mactans), native to North America, and the Katipo (L. atricus), native to New Zealand.

mature female Red-back This mature female Red-back has a dark-brown body and an orange-red dorsal stripe.
Image: Tim Blackburn
Source: Museum Victoria

First described scientifically in 1870, it was thought that the Red-back may have been a recent arrival to Australia since it was first reported some time after European settlement, from the port town of Rockhampton in central Queensland. Widow spiders can survive for months without food, and this enables them to travel long distances in cargo. The Red-back, however, is considered to be an Australian native by most experts, because of some notably distinctive characteristics that it does not share with overseas widow spiders.

Adult female Red-backs have a body length that is three to four times that of adult males, with females typically being 10-15mm long. Only females possess bright red or red-orange markings. They are usually black (sometimes dark brown) when mature, whereas males are usually light brown with white markings.

Juvenile female Red-back Spider in web Juvenile female Red-backs have different markings and colouration to the adults. This one is resting in the snare of her web.
Image: Patrick Honan
Source: Museum Victoria

Red-backs are found in all but the most inhospitable of Australian environments. They are usually found in their webs which they usually weave close to the ground in dry, sheltered areas, such as under rocks and logs, in junk piles, in sheds and outdoor toilets, and in empty tins and bottles. Electric lights and food scraps in people's houses and other buildings attract moths, flies, cockroaches and mosquitoes, which Red-backs feed on, and this may explain why these spiders prefer to live in and around places of human habitation over natural environments.

Red-back in Bugs Alive exhibition The Bugs Alive! Red-back display demonstrates a kind of habitat that Red-backs prefer. This one is littered with empty cans and containers and is kept relatively dry.
Image: Tim Blackburn
Source: Museum Victoria
 

The web of the female Red-back is an irregular mess of fine but strong silk. It usually contains a funnel-like upper retreat where the spider rests during the day, under which rests a mass of entangled, sticky strands that form a snare held to the ground or a wall by a number of trip-wires. These trip-wires contain globules of glue and are very elastic. When an insect or small vertebrate walks into one, the trip-wire snaps and catapults the victim into the snare above. Then the spider approaches its victim, wraps it in silk and bites it to envenomate and kill it. Male Red-backs do not spin webs and simply feed on prey items they salvage from the edge of the female's web.

Red-back spider feeding on large cockroach The Red-back’s web enables it to catch prey much larger than itself. This immature female is feeding on a cockroach that is more than twice its own body length and also much broader.
Image: Patrick Honan
Source: Museum Victoria
 

The venom of the Red-back is neurotoxic to humans, triggering an uncontrolled release of neurotransmitters – the chemicals that transmit signals between nerve endings. This can cause paralysis in the bite victim when the venom’s action severely depletes the neurotransmitter reserves required for normal muscle function. Most human victims of Red-back bites suffer little more than localised pain and swelling. In severe cases, however, bites can lead to chest and abdominal pain, nausea, vomiting, fever, muscle spasms, convulsions, coma and death (more likely in the young, elderly and frail). Before the development of an antivenom in 1956, at least 12 deaths had been recorded. The antivenom is assumed to have saved many lives as there have been no deaths since it became available - despite an increase in the number of bites reported. This increase is thought to be a consequence of expansion of habitats suitable for Red-backs in the urbanisation of Australia’s cities, and associated increases in human urban populations.

Links:

Red-back Spider infosheet

Bug of the Month - Prickly Katydid

Author
by Patrick
Publish date
1 January 2012
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Prickly Katydids, or Spiny Tree Crickets, occur from the rainforests of northern New South Wales to Iron Range in Far North Queensland. There are four species of Prickly Katydids but the most common is Phricta spinosa. It has the rather long official common name of Giant Spiny Forest Katydid and is found from Innisfail to Cooktown. Those that know and love this species simply call it Phricta.

Prickly Katydid. The spiny countenance of a Prickly Katydid.
Image: Patrick Honan
Source: Patrick Honan
 

During the day, Phricta sits motionless on bark or amongst twigs with its legs held out straight where it is remarkably well camouflaged. Some bird species, particularly Black Butcherbirds, move up and down tree trunks trying to disturb the insects so they will give themselves away. When threatened, Phricta will point its back legs skyward, revealing rows of sharp spines and red patches at the bases of the legs. These red patches appear to discourage predators.

adult male prickly katydid The legs of this adult male bear the black and orange markings of its startle display.
Image: Patrick Honan
Source: Patrick Honan

Adults have a body length of 10cm or so, and their highly sensitive antennae may be three times that length. Adults are normally found high in the rainforest canopy, but after mating, the female glides to the ground to lay her eggs in the soil.

Prickly Katydid laying eggs An adult female pushes her abdomen into sandy soil to deposit a batch of eggs
Image: Patrick Honan
Source: Patrick Honan
 

The young Phricta feed low in the understorey on the constant 'rain' of flowers and buds from above.

A young nymph feeding on a fallen flower bud. A young nymph feeding on a fallen flower bud.
Image: Patrick Honan
Source: Patrick Honan

Phricta moult several times before reaching adulthood. Moulting takes place during the first part of the night and they are very vulnerable to predators at this time. The elongated antennae may take a long time to withdraw fully from the old skin.

Phricta moulting at night. Phricta moulting at night.
Image: Patrick Honan
Source: Patrick Honan
 

The colours of juvenile Phricta are variable and help camouflage them against tree trunks and lichen-covered bark.


Juvenile prickly katydid Juvenile Phricta are often beautifully patterned with greens and browns. The budding wing pads can be seen between the spines of the legs and thorax.
Image: Patrick Honan
Source: Patrick Honan

juvenile Phricta. A lichen-coloured specimen with a radically different colour pattern to other juvenile Phricta.
Image: Patrick Honan
Source: Patrick Honan

After reaching adulthood, Phricta can be found higher in the canopy, feeding on the young leaves of trees and shrubs. On particularly windy or stormy nights, they will move down into the lower canopy or into tree holes to shelter from the weather.

ovipositor of Phricta The long, sword-like ovipositor is visible at the end of this juvenile female's abdomen. Her oval-shaped 'ear' can also be seen just below the 'knee' of her right foreleg.
Image: Patrick Honan
Source: Patrick Honan

Like most katydid species, male Phricta call loudly to attract females in the rainforest at night, a sound familiar to people who frequent these forests. Females possess an auditory tympanum (or ear) on their forelegs to pick up the call.

Parasites on the thorax of juvenile Phricta. Parasites on the thorax of juvenile Phricta.
Image: Patrick Honan
Source: Patrick Honan
 

Phricta are attacked by owls and other predatory birds, as well as honeyeaters and brush turkeys. They are also host to parasitic mites, which gather sometimes in large numbers on the top of the thorax. The effects of these mites on the insects are not known.

Phricta can be seen in the 'Diversity' display in Bugs Alive! at Melbourne Museum. Despite being very common and widespread in North Queensland rainforests, this species was not described scientifically until 2005, an indication of how much is still to be discovered and catalogued by science.

Further reading:

Rentz, D., 1996, Grasshopper Country: the Abundant Orthopteroid Insects of Australia, University of New South Wales Press, Sydney, 284pp.

Rentz, D., 2010, A Guide to the Katydids of Australia, CSIRO Publishing, Collingwood, 214pp

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