Hunting the Hunter (Part 1)

You would think that a spider as robust (and venomous) as a huntsman spider (Sparassidae) would be pretty safe from predatory and parasitic insects. But not so. This article is the first in a series on the insects which make a meal of large spiders.

A few years ago I witnessed a titanic struggle taking place on a window at the front of our house. A large spider hunting wasp (or ‘spider wasp’) was pulling a huntsman spider backwards up the window glass.

Wasp and huntsman

This spider is a female of the species Cryptocheilus bicolor of the order Pompilidae. These gorgeous black and orange wasps find a large spider and sting it to paralyse it.The female spider wasp doesn’t feed on the spider herself – the spider is food for her offspring.

Earlier that day I had seen our wasp digging a nest hole in the sand bank at the rear of our house. Many species of spider hunting wasps place their prey in a nest in the ground (one spider per cell) and lay a single egg on it. The hatching wasp grub feeds on the live but immobilised spider.

I saw her trying to fly with the spider but she could barely lift it off the ground – her wings were damaged as you can see from the image above. Dragging the spider was her best option and she was attempting a shortcut up over the house rather than going all the way around!

The glass was slippery and the spider was heavy and down down down she would slip – sometimes all the way to the ground. Each time she fell down she started the climb again. I have no idea why she insisted on going up glass rather than up the house bricks where she would have had more grip.

Eventually after about half an hour of this frustrating struggle she gave up and began hauling the spider around the house – a distance of about 50 meters. She accomplished the task of dragging the spider to her nest in just a few minutes. After about an hour she emerged from the nest and flew away. I assume she had laid her egg and had no more interest in the nest.

When spider wasps move around on the ground they move in a jerky ‘stop start’ manner and constantly flick their antennae and wings. The video below shows typical spider wasp behaviour (featuring a different individual to the one described above).

 

There are about 230 species of spider hunting wasps (Pompilidae) found in Australia. This is only one of the groups of insects which attack spiders – there are many more. The image below shows some insects from one such group. What are they? You’ll have to wait for the next ‘one minute bugs’!

insect

 

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Said the Spider to the Fly

“Will you walk into my parlour?” said the spider to the fly;
“’Tis the prettiest little parlour that ever you did spy.
The way into my parlour is up a winding stair,
And I have many pretty things to show when you are there.”
“O no, no,” said the little fly, “to ask me is in vain,
For who goes up your winding stair can ne’er come down again.”

This early 19th century poem by Mary Howitt paints a picture of a cunning spider trying to entice a fly into its web. In real life web-spinning spiders don’t try to inveigle flies, or any other form of insect, into their webs. Spider webs are spun across an area where prey is likely to fly or wander through, and (hopefully) blunder into (and get entangled in) the web. According to research, spiders collectively consume somewhere between 400 and 800 million tons of insects per year. Spider webs work pretty well then!

Orb web

Spider webs are made from spider silk which is produced from a number of silk glands located in the spider’s abdomen. The silk at this stage is a viscous liquid consisting of about 50% proteins and a mixture of other substances. The silk is extracted through special finger-like organs called spinnerets, which cause the protein molecules to align and form solid silk.

Modern web-spinning spiders have three pairs of spinnerets and each pair does a different job. The silk from the front spinnerets is used for attachment points, drag lines, and in the construction of the main frame threads of a web. The middle pair of spinnerets produce swathing silk used to wrap up prey and spin egg sacs. The rear spinnerets produce the gluey silk used in orb web construction.

Weight for weight, spider silk is up to 5 times stronger than steel of the same diameter. A silk fibre is approximately one micrometer in diameter which is about 80 times thinner than human hair. Male spiders often have fewer silk glands than female spiders – after all a male spider’s only purpose in life is to mate with females. Females need their full assortment of silk glands for web building, prey capture, and egg sac production.

Orb spider

Orb-weaving spiders, such as garden orb-weavers (Eriophora spp.), are very common in gardens, crops, vineyards and nurseries, and there are about 100 or so species scattered throughout Australia. These spiders usually construct a web in the evening and take it down at dawn. These orb webs are stretched across open spaces, which begs the question: How does a spider get her first thread across that open space?  She releases a long thread of silk which drifts in the breeze until it lands on something solid. If the attachment is to her liking she commences construction of the web proper, a process which takes about an hour. The web will be strong enough and flexible enough to stop a large insect flying into it at full speed. If the web was rigid rather than flexible it would break under such force. Garden orb-weaving spiders, like all other spiders are predators, meaning they are a beneficial presence in any garden, nursery, vineyard etc. The one in the image above has snared an Australian plague locust (Chortoicetes terminifera).

A web building spider may produce an egg sac containing hundreds of eggs. When those eggs hatch into spiderlings you might think the web would become overcrowded, but spiders have a clever solution for this potential problem. The spiderlings release a thread of silk which is picked up by the breeze and the spiderlings ride the air currents. This technique is known as ‘ballooning’ and spiderlings may be carried high up into the stratosphere and travel thousands of kilometres.

Sometimes there are mass ballooning events where many thousands of spiderlings descend on an area. There are numerous examples that will show up in a Google search. The media has a field day with these events, and they scare the living daylights out of arachnophobes everywhere. I guess nothing instills fear in arachnophobes more than the idea of venomous spiders raining down from the sky! Fear not – they are harmless baby spiders.

Orb weaving spider

My favourite web building spiders are the golden orb-weaving spiders (Nephila spp.) (pictured above). The ‘golden’ part of their common name refers to the colour of the web, not the colour of the spider itself. Their webs are huge, as much as a couple of meters across, permanent, and very strong. I know this from personal experience as I have blundered into them several times and basically bounced off! The webs are very complex, with a fine-meshed orb suspended in a maze of non-sticky barrier webs.

Female golden orb-weaving spiders sit head down in the middle of their orb waiting for prey to fly into the web and get stuck on its sticky threads. After she consumes the prey the remains are stacked into a string of debris in the centre of the orb. There is some debate about the purpose of this debris string – one of the theories is the debris alerts birds to the presence of the web so that they don’t fly into it and break it.

Finally, spiders shouldn’t be overlooked when it comes to insect pest management. I was amazed by the number of spiders I found in vineyards during my time with an Integrated Pest Management consultancy. In many cases spiders were the most numerous beneficial organism by far. Spiders are good!

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Simply irresistible

The Grampians region of Victoria is one of Australia’s richest and most diverse flora areas. One third of Victoria’s flora is represented here so it is no surprise that the region was once dubbed “the Garden of Victoria” by the great botanist Ferdinand von Mueller.

Spring is an excellent time to see wildflowers throughout the region, especially terrestrial orchids such as the Mantis Orchid (Caladenia tentaculata) pictured below. It is one of the green-comb Spider Orchids and is common throughout the Grampians region. The colourful and flamboyant flowers of this orchid may be pleasing to the human eye but they are simply irresistible to certain male insects.

Caladenia tentaculata

The Mantis Orchid is one of many sexually deceptive orchids. Orchids such as these don’t have nectar to reward pollinating insects so they must attract insects some other way.  The orchids lure male insects to their flowers with scents that mimic female insect sex pheromones. The labellum of the flower where the male insect lands is hinged and swings the insect against the sexual organs of the flower. During its struggles to mate with the flower the insect will either pick up pollen, or deposit pollen that it has acquired from another flower.

The insect pollinator of the Mantis Orchid is a thynnine wasp of the family Tiphiidae. These wasps are the most important insects which pollinate Australian terrestrial orchids by pseudocopulation. The wasps are also remarkable because males are winged and females are wingless. A female wasp finds a mate by advertising her presence with pheromones, the male picks her up and mating occurs in flight. It is quite common to see mating pairs flying around our property. A mating pair of thynnine wasps is pictured below.

Thynnine wasps

All this flying around while mating means the wasps stay in a coupled position for a prolonged period of time. To facilitate this, both sexes have evolved unusually shaped genitalia that include spines, grooves and other structures, so that they don’t accidentally disengage. But why don’t the females have wings? Some female flower wasps are parasites of beetle larvae and mole crickets located underground. Winglessness allows females to dig underground and hunt for prey without risking damage to delicate wings. This probably sounds exotic and unusual, but wasps of the family Tiphiidae are common in Australia, in fact we have about 700 native species.

Thynnine wasps are not the only insects lured into pseudocopulation with native orchids. I think I have space for one more story which should be titled “How not to photograph a pseudocopulating insect“. One November some neighbours showed me Large Duck Orchids (Caleana major) flowering on their property. As you can see below they are spectacular flowers that resemble flying ducks, so I grabbed my camera for some shots.

Caleana major

Within minutes of me starting to shoot the orchids an insect arrived and landed on one of the flowers. “Holy cow”, I thought. “It’s the pollinator!” Heart racing I tried to capture the insect but in my excitement I tripped over my tripod and almost flattened the orchid! By the time I got myself organised the insect, a type of sawfly, was trapped inside the orchid and was barely visible. I did get a couple of shots of the insect emerging but they are pretty terrible (see below).

Duck Orchid pollinator

How did the orchid trap the insect? The ‘head’ of the duck is the lid of a trap which swings down by the ‘neck’ trapping the insect inside the ‘body’. In it’s struggles to escape the insect is covered with pollen and will transfer that to the next flowering Large Duck Orchid it is attracted to. Hopefully one day I can have another crack at these shots and try not to be overwhelmed by the occasion!

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Historic weevil

I first published this story back in April 2015. Recently, I spoke about this weevil on ABC Radio Ballarat and also at a talk I gave to Friends of the Grampians Gariwerd (FOGG) so I thought now is a good time to republish.

I found this fellow trundling along the road when I went for my morning walk the other day. This insect is commonly known as a Botany Bay weevil (Chrysolopus spectabilis) or by its other common name “diamond weevil”. This is the male of the species. Females are larger insects, making males the lesser of two weevils (sorry, I couldn’t resist!).

Botany Bay weevilBotany Bay weevils belong to an historic group of insects. This weevil was collected by Sir Joseph Banks on Captain James Cook’s voyage to Australia in 1770. Actually we don’t know that Banks himself collected it – it could have been one of his men, or the Swedish naturalist Daniel Solander who accompanied Banks on the voyage. On his return, Banks gave the task of cataloguing his insect collection to the Danish insect taxonomist Johann Fabricius. The weevil was described in 1775, making it one of the first (if not the first) Australian insects described to western science.

Sydneysiders may be surprised to learn that the Botany Bay weevil is not only found around Sydney, but from coastal far north Queensland to eastern South Australia. The weevil is certainly common in New South Wales and its common name probably dates back to the early colonial days of Botany Bay.

To this day we don’t actually know where Banks’ specimen was collected. Was the weevil collected at Botany Bay in April 1770, or during July/August 1770 when Cook was repairing the Endeavour near present day Cooktown, or at one of the other landing points in between? The label on the specimen simply says “nova Hollandia”.

Botany bay weevil femaleBotany Bay weevils are associated with about 30 species of Acacia. Female weevils chew holes in stems at or below ground level in which they lay their eggs. Upon hatching the larvae bore into the stem and usually down into the roots. Adult weevils emerge in the summer, and what spectacular insects they are with their rich metallic green or blue markings on a black background. The adult weevils also feed on Acacia spp. in their characteristic manner of removing the leading shoots several centimetres down the stem.

The Botany Bay weevil has a distinctive defence mechanism. One day I was taking some close-up images of weevils on Acacia provincialis when I got just a bit too close for comfort. The weevil suddenly went stiff, toppled backwards and fell to the ground like an actor in a B grade Western movie. The trick I learned was to move closer to them slowly, taking photos as I went, so they got used to me and the noise of the camera.

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Sap-suckers & sooty mould

Sooty mould is not a plant disease as such but various species of fungi, which grow on the sticky honeydew excreted by many species of sap-sucking insects. A very thick mould layer on leaves may cause a reduction in photosynthesis in plants, which can result in leaves falling prematurely. The main concern to gardeners (apart from the sap-sucking pests which caused it) is that a thick covering of sooty mould on a plant’s leaves is downright ugly.

Sooty mould is a serious problem for the horticultural industry. Ugly plants are unsaleable. Similarly in the citrus industry, the main economic damage caused by mealybugs is by the downgrading of fruit quality due to sooty mould growing on mealybug honeydew. The picture below shows a leaf infested by soft scale insects and the sooty mould they cause – pretty ugly eh?

Sooty mold

Continue reading Sap-suckers & sooty mould

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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.

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

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