This is Diplora, our pet praying mantis.

Diplora, with (another) meal

Diplora, with (another) meal


We have kept praying mantis’ before. Diplora joined the team when she was still very small – to start with we fed her Drosophila (fruit flies) from our compost bin.

Diplora consuming a fruit fly

Diplora consuming a fruit fly (while upside down on the roof of a glass box)

Like other insects, praying mantis’s get their shape from a stiff exoskeleton, so to get larger they shed this outer layer from time to time.

Diplora in the process of moulting

Diplora in the process of moulting

Diplora has done this 3 times since we got her and we suspect she only has one more moult to go before she (or he) becomes fully adult.

Several exoskeletons from one mantid as it grew larger

Several exoskeletons from one mantid as it grew larger

One of the interesting things about this process (ecdysis) is that the exoskeleton retains a lot of the fine detail of the mantid, but with the advantage that we are able to examine it in detail – because unlike Diplora, the exoskeleton stays still while you have a good look at it.

Exoskeleton showing the compound eyes

Exoskeleton showing the compound eyes

We have enjoyed looking at details such as the compound eyes, the spikes on the forelegs, mouthparts (mandibles) and their fine antennae.

Exeskeleton showing antennae and the eyespots on the arms

Exeskeleton showing antennae and the eyespots on the arms

Exoskeleton showing detail of forearms and an eyespot on the arm

Exoskeleton showing detail of forearms and an eyespot on the arm

Detail of abdomen

Detail of abdomen

We have not yet fully captured the process on video, but here is some footage from someone who has (for a different species of mantid).

Compound eyes and pseudopupils

One thing that puzzled us with our mantids was the appearance of black dot in each eye – which isn’t always there, depending on the light. You can see it in the photos above, especially the one at the top. This is known as a “pseudopupil” and is essentially an artefact of the viewer. The compound eyes are made of many cones, with lenses over each. The lenses reflect some light, but in one position, relative to the viewer, no light is reflected, and so a dark spot appears.

This site has a series of photos of all kinds of insects showing this effect.

It is lady beetle season here. There are dozens of the larvae in our garden, so we collected some up and have been watching them, and feeding them aphids and mealy bugs. The larvae moult several times, getting larger each time.

Lady beetle larvae

Lady beetle larvae

We weren’t sure what species they would be. We didn’t find any kind of overview with information about the species that are in NZ, which are both native and introduced. It is  especially difficult to find information about the larval stage.

After a couple of days, the first few larvae started to pupate. The pupa was a yellowy colour, later becoming much darker – almost black.

Pupating larvae on left, larvae on right

Pupating larvae on left, larvae on right

One evening, about a week later, the first beetle hatched. At this stage it was a pale cream colour.

Emerging from the pupa stage

Pupa after a beetle has emerged

Pupa after a beetle has emerged

chaos ladybeetle newly emergeDSC_2701

By the morning it had turned the classic red and had two black spots. So probably, we have Adalia punctata. We now have about 8 beetles, apparently all of the same species.

We have since found a little more information, including  this paper here. There is also information on the Coccinellidae family on Wikipedia.

The beetles don’t seem to be quite so keen on the mealy bugs, but are enthusiastic about the aphids.

Ladybeetle and aphids, on a rose bud

Ladybeetle and aphids, on a rose bud

And we now have several bright orange clusters of  lady beetle eggs. Quite a few clusters of eggs were laid, but also quite a few of those were eaten by the beetles themselves. Lady beetles are described as ‘voracious’ feeders, with some eating 1000 aphids in a life time.

chaos ladybeetle eggs DSC_2664

Cluster of lady beetle eggs

The whole life cycle was quite quick and we can recommend these as a species to try, if you would like to keep some insect pets.

Life cycle of the 2-spotted lady beetle. A, the adult beetle. B, group of eggs on under surface of a leaf. C, a young larval beetle covered with white wax. D, the full-grown larva. E, the pupa attached to a leaf by the discarded larval skin

Life cycle of the 2-spotted lady beetle. A, the adult beetle.
B, group of eggs on under surface of a leaf.
C, a young larval beetle covered with white wax.
D, the full-grown larva.
E, the pupa attached to a leaf by the discarded larval skin

It is Autumn here. There was fog lying on the ground in Hagley park this morning. It was a beautiful day.

CINJAT Hagley Park IMG_3398

CINJAT Hagley Park IMG_3400

CINJAT Hagley Park IMG_3418

CINJAT Hagley Park IMG_3422

CINJAT Hagley Park IMG_3429

While out and about recently, we have been uploading a few photos of plants and animals that we have seen to a web site called ‘Project Noah‘ – the Noah stands for ‘networked organisms and habitat’. Backed by National Geographic, Project Noah is a citizen science project documenting the worlds organisms.

Opening screen for Project Noah

Opening screen for Project Noah

You can use an iPhone or Android app to upload a ‘spotting’ while you are out, or, you can use the web interface of a computer to upload photos. Videos can also be included, along with notes and links to further information on other sites (Encyclopaedia of Life, Wikipedia). You can even request help with identification of your find.

Screen for data entry

Screen for data entry

The ‘field guide’ mode shows you the species that other people have found nearby. Once you find something relevant, there is often a link to additional information. It is also possible to ‘follow’ other participants, and to make comments on other peoples spottings.

Some of the arthropod species recorded nearby

Some of the arthropod species recorded nearby

Part of the goal of the app is to enable people to contribute sightings that are of particular interest to researchers. This ‘citizen science’ aspect is supported by the ability to assign photos to any relevant ‘missions’. Some of these are location based (e.g. Biodiversity of the Galapagos), while others are more focused on a particular taxonomic group (e.g. Monarch Migration). And what’s more, anyone can download the data for a mission.

Something we have found frustrating is that it is apparently not possible to search all the missions. Only some missions appear on the list you can look through. We have only discovered some of the most relevant missions to where we are (Christchurch, New Zealand) by noticing a mission link on someone else’s spotting.

You can also create your own missions, although we have been reluctant to start a new one until we can determine what is already underway nearby. This would be a great tool for a BioBlitz project.

Some of the current missions current

Some of the current missions current

Nevertheless, we are enjoying the challenge to find and document more species while we are out and about. Here is our favourite find so far – an Australian leafroller tachinid fly, introduced to NZ for biocontrol of some apple moth pest species (although we are not entirely confident that we have the correct identification).

Sighting for Project Noah 'Flies!' mission

Sighting for Project Noah ‘Flies!’ mission

The youngest and most eagle-eyed of us spotted a jumping spider making a meal of a fly. The fly had landed in the middle of a window pane and spider grabbed it. An impressive feat.

Jumping Spider with Fly - side view

This spider has six eyes. The pair at the front move in tandem and give the spider 3D vision for approaching and catching prey.

Jumping Spider with Fly - looking forward

Jumping Spider with Fly - looking up

The next day, the dried husk of the fly was on the window ledge and the spider was back patrolling the windows.

One of us is 7, so obviously we made a trebuchet. Actually we have made several in the last year or so – the current version goes sufficiently high and far  to only be useable outside.

Trebuchet, about 68 cm to the axis

Trebuchet, about 69 cm to the axis

We used FischerTechnik, which allowed us to easily experiment with the design ourselves by adjusting each component.

This website was helpful in detailing what to aim for in the design.

Parts of the Trebuchet

Parts of the Trebuchet

The design features we found useful were:

  • The main frame needs to be quite sturdy – we used quite a bit of bracing
  • The optimum ratio for the length of the weight arm to the projectile arm is 1:3.75
  • The arm needs to be strong but light
  • The length of the sling (we used linen thread) should be about the same length as the projectile arm
  • The counterweight needs to swing freely
  • The mass of the weight should be about 100x the mass of the projectile
  • The angle of release (affected by the pin angle) should be about 45o
  • There needs to be a smooth surface for the projectile to travel along before it is launched (we used some cardboard to smooth the transition over the base)
  • Solid ground underneath helps (e.g. not carpet)
Trebuchet frame, with lots of bracing

Trebuchet frame, with lots of bracing

Weight - full of metal screws, weighing about 400 gm to match our projectile of approx. 4 gm

Weight – full of metal screws and weighing about 400 gm, to match our projectile of approx. 4 gm. There is a hinge connecting this weight to the end of the arm so that it swings freely.

Release pin for the sling, on an angle

Release pin for the sling, on an angle. Different angles produce very different results.

One of the projectiles.

One of the projectiles – this was the ‘medium’ weight version.

It is interesting to adjust various parts and see the effect. For instance,

  • small weight + 60o pin = 4.1 m range
  • heavier weight + 60o pin = 3.7 m range
  • small weight + 30o pin = 8.3 m range
  • medium weight + 30o pin = 8.7 m range
Drawing back the projectile, about to launch

Drawing back the projectile, about to launch

The projectile is difficult to see in a video, so we fired it at dusk with LEDs attached to the projectile:

Trebuchet fired at night, with red LEDs and battery attached to the projectile

Trebuchet fired at night, with red LEDs attached to the projectile and showing its path.

And here is a video:

It would be nice to be able to provide a general description of the physics of how a trebuchet works, but it turns out to be rather more complicated than it initially appears. There is an explanation by Donald Siano here if you really want to get into it.

Physics explanations aside, they are quite satisfying to make and to fire. I expect our next (better, bigger) version will require trips to a park so as to be able to launch projectiles without losing them into the neighbours place.

Ash Keating has done a great large-scale artwork in central Christchurch – well worth a look if you are local. There is a video of him making it here.

Ash Keating: Concrete Propositions

Ash Keating: Concrete Propositions

We especially enjoyed the contrast to the rather desolate surroundings, where many buildings have been demolished, following the earthquakes of the last couple of years.

An adjacent buiding, with multiple cracks very visible.

An adjacent buiding, with multiple cracks very visible.

These sites have mostly been left flat, with a covering of rubble. Needless to say it is very dusty in town these days. More planting would be nice!

One of *many* cleared sites in central Christchurch.

One of *many* cleared sites in central Christchurch.

The backs and sides of buildings that were previously rarely seen are now very visible.

The back of a building, now visible.

The back of a building, formerly hidden.

A number of projects have been done or are underway to improve the general environment. And nature is doing its bit, to set things right.

A former footpath.

A former footpath.

Plants, apparently undaunted.

Plants, apparently undaunted.

These were providing habitat for insects too.

These were providing habitat for insects too.

So, in the midst of all this, we really enjoyed a concrete proposition:

Detail of a 'concrete proposition'.



Large scale art is great!

More, please.

We found some backswimmers in a water lily pond and bought them home to study. These bugs have an elongated pair of back legs for propulsion and swim on their backs (unlike water boatmen). They are predators, eating other pond invertebrates, including mosquito and other larvae.


They trap an air supply on hairs on their back. You can see the shiny bubble of air in the photo below.


The male animals stridulate, to attract a mate. This chirping sound is made by rubbing a rough area on their legs against their head. In spite of being underwater the sound is quite loud. When it’s quiet at night, you can hear them throughout the house. Here’s a recording of a couple of chirps.

This is the waveform. There are two short chirps three-quarters of a second apart, followed by a string of closely spaced chirps. Typically there are five chirps, but we have observed up to a six and as few as two chirps in the sequence.

Zooming in on a single chirp, it’s a 5kHz tone with an 800Hz modulation.

We have a “carnivore corner”, a collection of carnivorous plants. The sundew has just flowered. Like many carnivorous plants the flowers are held high above the rest of the plant on a long stem. The long stem may serve to keep the pollinators from being eaten, though where the pollinators are not the same species as prey, it may be to maximise exposure of the flowers to the pollinators.

Sundew flower stalk

The flowers show five-part radial symmetry and are about 10-15mm across.

Sundew flower detail

There are a series of flowers on the stem. Each flower, in turn, opens in the morning and closes at nightfall, never to open again. The next day, the following flower opens.

Sundew flower head

The sundew catches small insects when they blunder into the sticky mucilaginous goop that sits on the ends of the stalks that cover the leaves.

Sundew leaf

Once the insect sticks, the leaf rolls up around the prey enmeshing it. The mucilage contains enzymes which digest the insect and the resulting ‘soup’ is absorbed by the leaves. The photo below shows a fruit fly trapped by the plant.

Sundew with prey

Simple, but weird.

All you do is add water to corn flour (sold in some places as corn starch), aiming for a ratio of approximate 2:3 of water to cornflour.

You can do this on a small scale, say in a cup, and it will be interesting. But if you can, we recommend a rather larger quantity. We found kg bags, for a few dollars each, at a local Asian food warehouses.

Take your time to mix the water in, as the components act bizarrely, even at this stage, with the spoon slipping across the surface unless you mix very slowly.

What happens?

When a force acts on the mixture, e.g. if you try to mix it quickly, it acts like a solid. But if there is only a small force acting, e.g. if you mix slowly, the mixture will act like a liquid. So you can pick up a piece that feels like a solid lump, but if you try to hold onto it, the mixture will become liquid again and drip off your fingers.

The viscosity increases with force. A fluid that behaves like this is described as a non-Newtonian shear-thickening fluid, or a dilatant fluid. A 'normal' (or 'Newtonian') fluid has the same viscosity (flow) regardless of the force applied.

You have probably also encountered a shear-thinning non-Newtonian fluid. These are mixtures that become more fluid (less viscous) when a force is applied, and toothpaste is an example – that is how you can get it out of the tube but it doesn't drip off your brush.

There is a diagram here that compares these types of fluids, and Wikipedia discusses non-Newtonian fluids here.

But why?

Its been difficult to find an explanation for what is actually happening. The closest I found was by RP Chhabra here. Apparently the spaces between the starch molecules are filled by water when there is no/small movement. But when a stronger force is applied the molecules expand ever so slightly, such that the water is no longer sufficient to fill the spaces, and then the friction between the starch molecules becomes more significant.

There is also an analogy to a snow plough here, which compares the increased resistance to the way snow builds up in a solid pack when you push into it.

PS When you're done, don't tip this down the drain…


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