Cryptic Stick Insects - now you see them, now you don't
Stick insects (rō in Māori) are curious creatures. Kids (and adults) find them fascinating because of their obvious likeness to sticks. It's easy to spot them walking across a window or on the side of the house but they merge so well into their surroundings on a tree that you might be surprised just how many are in your garden.
These large, intriguing vegetarians are everywhere, although they seem to have trees that are their favourites.
Sitting in my garden recently, I recalled how many stick insects I'd seen on a particular tree in February last year. I looked at the tree, a mānuka, and idly said to myself "I wonder why there aren't any there this year". Curiosity drew my gaze back to the tree, suddenly I realised I could see a stick insect where before I thought the bark was bare. I looked harder, another stick insect 'appeared'. I got closer and started to count - there were a dozen stick insects in a 25 cm x 30 cm area!
The word to describe this kind of camouflage is 'cryptic'. It's both fascinating and confounding. I'd start counting in one area, looking, I thought, very carefully, and then move on to another, but when I went back to the beginning I'd have to work hard to pick them all out again.
Here's part of the image above enlarged. There are at least 7 stick insects to be seen!
Here they are, a pink line sits next to each of them. (Note there may be more but these are the ones I can see!)
I've read that stick insects are mostly nocturnal, but these seem to have barely moved from this spot for days. I wonder if there is some sort of social activity going on? I haven't seen any mating - not all stick insects mate, some are female-only populations. In that case, the females lay eggs without mating, so the DNA of the young are an exact match to the mother. This is called parthenogenesis.
Here was the diagram I drew of the stick insect gathering in my Nature Journal on another day. I put a T or H to indicate tail or head.
Every now and then there is a bit of movement, one or two of the insects sway. Scientists aren't sure why they do this. (I couldn't help thinking there was some sort of communication going on between them.) See the video below.
A green stick insect turned up during the week, hung around for an hour or two and then left the tree and went elsewhere. Apparently being green or brown doesn't indicate a different species or sex, and they don't change colour to suit their surroundings.
A favourite resting position seems to be with front legs folded in front, making them look a little like a four-legged animal with two antennae. But their antennae are tucked between the front legs.
Some websites I enjoyed reading about stick insects.
Landcare Research https://www.landcareresearch.co.nz/science/plants-animals-fungi/animals/invertebrates/systematics/phasmatodea
New Zealand Geographic magazine https://www.nzgeo.com/stories/stick-insects/
Massey University http://evolves.massey.ac.nz/Text%20Files/Stick%20insect%20eggs.htm
Using the information in the Landcare Research site, I think that these stick insects are of the Clitarchus hookerii species. Now I just need to find some of their eggs to confirm this.
These large, intriguing vegetarians are everywhere, although they seem to have trees that are their favourites.
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| Stick insect on its favourite mānuka tree |
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| Hiding in this image are many stick insects quite a few of them are in the grass and look just like stalks of grass! |
Here's part of the image above enlarged. There are at least 7 stick insects to be seen!
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| Spot the stick insects! |
Here they are, a pink line sits next to each of them. (Note there may be more but these are the ones I can see!)
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| 7 stick insects marked in pink |
Here was the diagram I drew of the stick insect gathering in my Nature Journal on another day. I put a T or H to indicate tail or head.
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| From my Nature Journal, the dark lines show the 11 stick insects I observed |
A green stick insect turned up during the week, hung around for an hour or two and then left the tree and went elsewhere. Apparently being green or brown doesn't indicate a different species or sex, and they don't change colour to suit their surroundings.
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| This green stick insect is facing down the tree trunk, its front legs are folded together and point downwards |
Some websites I enjoyed reading about stick insects.
Landcare Research https://www.landcareresearch.co.nz/science/plants-animals-fungi/animals/invertebrates/systematics/phasmatodea
New Zealand Geographic magazine https://www.nzgeo.com/stories/stick-insects/
Massey University http://evolves.massey.ac.nz/Text%20Files/Stick%20insect%20eggs.htm
Using the information in the Landcare Research site, I think that these stick insects are of the Clitarchus hookerii species. Now I just need to find some of their eggs to confirm this.