Tim Blackburn

DISPLAYING POSTS BY: Tim Blackburn (4)

Tim Blackburn

Tim worked as a keeper for Live Exhibits 2008-2013. He completed an Honours project on the foraging behaviour of an Australian frog species in 2009 at Monash University.

Bug of the Month - the mosquito

Author
by Tim Blackburn
Publish date
4 February 2013
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Mosquitoes are midge-like flies comprising the family Cucilidae. There are over 3,500 species of mosquito described worldwide and most of these require vertebrate blood as the principal portion of the female diet. The blood provides protein for egg development and maturation, and the lipids it contains are an energy source. Females possess elongated piercing and sucking mouthparts for obtaining their blood meals. Males obtain all their energy from sweet fluids such as nectar and honeydew. Since they don't lay eggs, male mosquitoes do not require a protein source and do not bite.

Close-up of female mosquito The elongated proboscis of this female mosquito enables it to obtain the protein it requires for egg development and maturation.
Image: sondebueu
Source: sondebueu via cc
 

Adult females lay eggs in or near water, commonly on vegetation, a few days after a blood meal. The life cycle includes four larval stages, or instars. Between each instar the larva moults in order to grow. The larvae, or 'wrigglers' (so-called due to their characteristic movement), typically inhabit stagnant water bodies, and must come to the surface periodically to breathe through spiracles or a siphon. The larvae of some species use their mouth bristles to filter water for microorganisms, while others scrape food particles off the surfaces of submerged objects. The pupa does not feed but must come to the surface to breathe through respiratory trumpets.

mosquito larva The mouth bristles, used in filter feeding, are clearly visible on this wriggler. Note also the three body segments and the segmented abdomen.
Image: Tim Blackburn
Source: Museum Victoria
 

Female mosquitoes inject saliva that contains an anticoagulant into their host to prevent blood-clotting. The saliva also contains components that cause vasodilation (to increase blood blow) and suppress the immune response of the host (to protect the mosquito). Once the feeding episode ends, the host produces antibodies which trigger a release of histamine. This in turn increases the permeability of adjacent blood vessels, thereby enabling a stronger immune response. The blood vessels swell and this causes the familiar, itchy lump—the 'mozzie bite'.

Female mosquito A female mosquito just after landing on my toe as it commences a blood meal. Note the thin abdomen at the start of the meal.
Image: Tim Blackburn
Source: Museum Victoria
 

Female mosquito feeding The same mosquito one minute later. Note the swollen abdomen which is red because it is full of my blood.
Image: Tim Blackburn
Source: Museum Victoria
 

Viruses and pathogens are easily transferred between mosquito and host via the saliva. Mosquitoes are serious agents in the transmission of diseases such as dengue and yellow fever, malaria and lymphatic filariasis. In 1996, the World Health Organisation estimated that several million people die each year from mosquito-borne diseases around the world. Each disease is spread by a specific type of mosquito; malaria is spread by Anopheles spp. and dengue fever is primarily spread by Aedes aegypti.

However, mosquito-borne diseases are rare in Victoria, and mosquitoes here are more likely to annoy rather than cause disease. You can prevent bites by wearing insect repellent and protective clothing, and removing breeding sites. Window mesh and mosquito nets also help exclude potentially harmful species, particularly in tropical and subtropical areas. Various plant species such as Citronella Grass, Rosemary, Catnip and Marigolds repel mosquitoes and may be especially useful if planted near doorways and windows. 

Links:

CDC: Mosquito-borne diseases

Vector-borne diseases in Victoria

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

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

Daddy long-legs

Author
by Tim Blackburn
Publish date
20 September 2011
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Recently, a visitor to Bugs Alive! asked me whether daddy long-legs are spiders. The answer depends on what one is referring to when employing the term "daddy long-legs". It can be used to refer to a group of close relatives of spiders known as the harvestmen, which are arachnids (as are spiders) but are nonetheless not spiders. It can also be used to refer to crane flies, which are insects and not arachnids. The term is, however, most commonly used in Australia to refer to a species of spider known scientifically as Pholcus phalangioides. P. phalangioides is also sometimes known as the grandaddy long-legs, the cellar spider or the house spider, and is commonly found in houses in its irregularly structured webs which it often weaves in dark areas, such as under desks and behind bookshelves, or in the corners of ceilings in disused rooms.

The spider Pholcus phalangioides The spider Pholcus phalangioides is commonly referred to as the "daddy long-legs".
Image: Tim Blackburn
Source: Museum Victoria

Harvestmen, however, live in vastly different environments than does Pholcus phalangioides. They have been found in moist leaf litter, under rotting logs, under rocks and under the bark of trees. Unlike spiders, which are classified under order Araneae, harvestmen are classified under order Opiliones. The cephalothorax (the anterior/front body segment) of harvestmen is fused broadly with the abdomen (the posterior/rear body segment) to form a body which seemingly lacks a waist, whereas there is a distinct division between these two body segments in spiders. Furthermore, harvestmen have two eyes which are each positioned on the end of stalk-like projections found in a region approaching the top of the cephalothorax, as compared with spiders, which generally possess eight eyes attached directly to the anterior (front) region of the cephalothorax.

Harvestman specimen
Harvestmen are commonly referred to as “daddy long-legs” but they are not spiders. The above specimen’s second right leg appears blurry because harvestmen use their second pair of legs much like antennae, constantly waving them around.
Image: Tim Blackburn
Source: Museum Victoria
 

Harvestman on a leaf The two body segments of harvestmen are fused to give the appearance of a body with a much reduced or absent waist.
Image: Patrick Honan
Source: Museum Victoria
 

Unlike spiders, harvestmen do not produce silk, and they are omnivorous, having been known to feed on other invertebrates, plant matter, and the rotting carcasses of birds and mammals. They are non-venomous but can chew their food, whereas spiders must use venom injected by their fangs to convert their prey to liquid which they drink. Male harvestmen have a penis, which facilitates the direct transfer of sperm (from the genital region) to the female, whereas male spiders must use their pedipalps (which encircle the mouth) to do this indirectly.

Pholcus phalangioides
The distinct division between the two body segments of Pholcus phalangioides gives the appearance of a waist.
Image: Tim Blackburn
Source: Museum Victoria
 

Pedipalps of Pholcus phalangioides The bulbous terminations to the male’s pedipalps of Pholcus phalangioides are used to transfer his sperm to the female.
Image: Tim Blackburn
Source: Museum Victoria
 

pedipalps of harvestmen The pedipalps of harvestmen are used for food-handling only as males have a penis which enables the direct transfer of sperm to females.
Image: Tim Blackburn
Source: Museum Victoria
 

The Live Exhibits department sometimes has harvestmen in its collection. We are considering the merits of putting them on display in the near future, possibly to illustrate the differences between spiders and harvestmen.

Harvestman. A harvestman I recently found inside a house, oddly enough.
Image: Tim Blackburn
Source: Museum Victoria
 

Further reading:

Harvey, M. S. And Yen, A. L. (1997) Worms to Wasps. Oxford University Press, Oxford: p. 86-87.

Milledge, G. A. and Walker, K. L. (1992) Spiders Commonly Found in Melbourne and Surrounding Regions. Royal Society of Victoria, Melbourne.

Links:

Question of the Week: Daddy long-legs spiders

Harvestmen (CSIRO)

Harvestmen (Wikipedia)

Pholcus phalangiodes (Wikipedia)

Pholcidae (Wikipedia)

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Updates on what's happening at Melbourne Museum, the Immigration Museum, Scienceworks, the Royal Exhibition Building, and beyond.

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