This stick is walking without me! (Australian Spiny Stick Insect)

This week we are looking into one of the most popular stick insects around the globe! The Australian spiny stick insect happens to make a great pet and teaching tool, and it's got quite a few tricks up its sleeve. 

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This week's featured artists: Mitchel Logan and Blue Wednesday.

 

Transcript: 

 

It’s Tuesday! Or Monday for some of you and that means it’s time to talk about a cool insect with me as your host. We have another listener request episode this week from Chantelle out in Australia, and with that let's begin episode 42.

 

Australia's spiny stick insect is scientifically known as Extatosoma tiaratum, which translates to Ecstatic-bodied tiara! Quite the dainty name for something that looks monstrous to many. This big stick insect is native to Queensland and New South Wales which are both on the east coast of Australia, but because they happen to be easy to raise, and docile, these insects have been shipped around the world and used in various museums and educational facilities. I’m not saying they can be found in the wild around the world, but escaped populations might exist in Australia’s neighboring islands like New Guinea for example. 

 

These insects go by many names like Australian Walking Stick, Spinies, Macleay’s Spectre after the naturalist William Macleay who described them, Spiny stick insects, and spiny leaf insects. Now you might be confused about why it goes by both leaf and stick insects and I’m gonna clear that up right now.

Stick insects and leaf insects are terms for two different body shapes of insects in the order Phasmatodea, and as such are also divided by their family name. Leaf insects in the family Phylliidae are typically very flat and look like leaves while stick insects in the family Phasmatidae are usually more twig-like. Today’s spiny stick insect is indeed a stick insect within the family Phasmatidae, BUT! The females have a pretty ambiguous body shape that makes them look as if they could be a leaf insect too. And yeah I’m specifically talking about the girls here because this insect is sexually dimorphic which means males and females are pretty different. The females for this species are longer and a bit more thicc. They also have leaf-shaped arms with very small wings. The males on the other hand are thin with very long wings, and their legs do not widen out to the same leafy extent as their counterparts. 

I think the females are actually the most commonly photographed as well, but I’ll put pictures of both sexes up on the socials. 

 

So as I mentioned earlier these insects are very popular as both pets and exhibit insects for museums, and as such there is a wealth of knowledge about how to raise them and what they eat. Wild populations are known to feed on Eucalyptus, but they can also eat brambles like raspberry bushes, oak, and rose bushes as well. In fact, most domestic populations are raised on rose or berry bushes, because Eucalyptus isn’t exactly easy to get outside of Australia. 

 

The life cycle begins as an egg 2mm in length which is like the tip of a lightly used crayon, how do I know that? Because that’s what Google sensei told me. Anyway, here's where things get crazy. The eggs look like calico brown seeds, and not just to humans. 

 

Female spiny stick insects actually flick their eggs on the ground so that ants from the genus Leptomyrmex will take them home and keep them safe until they hatch! It gets even wilder because the seeds actually have a small plug called a capitulum that’s edible for the ants with no consequence to the stick insect. This is mimicry to the extreme to the point where the eggs even smell like ant food. I have no idea what that would be exactly but what I do know is that the ants keep these eggs in their homes until they hatch, which is a long time by the way. Like over 6 months of time and sometimes two years. The time it takes is dependent on the conditions of its environment. For example, dry and unsuitable weather might cause the egg to remain in this state for longer as opposed to a warm and relatively humid environment. Upon hatching these first instars actually resemble red-headed spider ants which also happen to be the ants which housed them.

 

After the stick insects hatch they begin their ascent into trees of host plants. In most wild cases that would be Eucalyptus. These small nymphs go through 5 molts if they are males and 6 molts if they are female with each one looking very much like a stick or dried leaves. Something really cool is that if a stick insect loses a leg while it is still a nymph, that leg will actually grow back in the next molt, just not as long as the original. That being said, if it's already an adult and loses a limb then it’s gone for good. In regards to their molting, these insects actually need to hang upside down on something for the best chance of having a clean molt. Their bodies are pretty big with females reaching a length of 20cm and as a result they rely on gravity to help them slip out. 

 

In the wild, these insects are preyed upon by birds, but they do a pretty good job at mimicking their surroundings. They even go as far as to sway their bodies like branches or leaves in a tree. One study actually looked at whether or not wind triggers stick insect body sways, and the answer was yes it does! 

 

Aside from blending into their surroundings, these stick insects do have some other methods of warding off predators. Both males and females if threatened will strike a pose that mimics scorpions by curling their abdomen up and elevating it by standing only on their front four legs. Males can also flare out their wings and both are able to release a defense odor that to us has a kind of toffee smell, but to other animals is gross, unless you don't like toffee. They also cross their hind legs in a defensive position to protect their backs. These insects are all bark and no bite though which is another reason they make great pets and educational tools for learning about insects. 

 

If you are interested in raising some of these yourself it's really not that complicated. You simply need a large enclosure with adequate air flow, and a heating source if you live in places where it gets colder than 16C or 60 degrees F in your home during the year. When it comes to food most people will take cuttings from raspberry, blackberry, rose or other known host plants and place them in a vase or jar with water. 

 

You need to be careful though, just because they can eat any of these plants does not mean the insects you receive will. Just like people, they have their individual preferences, so using what the parents were raised on is a good place to start since that is what they are genetically predisposed to wanting. 

 

These insects have a lifespan of 1 year in the wild but up to 2 in captivity. They are also a gift that keeps on giving because the females can lay up to 1000 eggs in their lifetime and they do not need a male for fertilization. The Australian spiny stick insects are parthenogenic which means that the females can produce viable eggs that are clones of herself! This is something I went into detail on in episode 26 with the web spinners so I’m not gonna say much more other than If you take good care of your sticks then you’ll never not have any.