Insects and spiders can’t grow steadily like we do because their skeletons are on the outside and serve simultaneously as skin, skeleton and armour. It doesn’t grow or stretch once it has hardened so the animal has to grow a new skin underneath the old one, crack the old one open and crawl out, and wait nervously until the new one toughens. I have seen different parts of the process in different insects recently so I thought I would put a group together.
Dragonflies: Juvenile dragonflies are so different from the adult it is hard to believe they are even related. They are water-dwelling predators which fishermen know as ‘mud-eyes’ and use as bait. After several moults in this form they climb up out of the water and split open to emerge as the winged adult dragonflies we know and love. I have yet to see it happen but here is a lovely photo from SE Qld.
Cicadas: Cicadas also undergo a radical change, since the nymphs live underground, emerging as stumpy-looking bugs with strong burrowing front legs and splitting open to emerge as a winged adult. I haven’t seen one emerging but here is a cast-off skin (known as an ‘exuvia‘), and here and here are some adults
Cockroaches: We have a resident population in our compost bin and I caught this photo recently of a just-moulted cocky resting next to its old skin. Like many (perhaps most) insects, fresh-moulted cockroaches are nearly colourless as well as soft; they darken as they harden.
Mantises: I found this cast-off skin eighteen months ago but I didn’t see one in the process of emerging until yesterday. It is one of the family I have been watching recently and described here. In terms of that post, this is a nymph with wing-buds emerging from one without. One photo of it is here and another is below.
In all cases, the amount of change from one stage (‘instar’) to the next is hard to believe. Even when they don’t change from swimmers or diggers to fliers, the difference in size makes you wonder how on earth that big bug fitted inside that little skin.
In human terms the changes would be (roughly) like changing from a one-year-old to a three-year-old overnight, then to a six-year-old, to an eleven-year-old and finally to an eighteen-year-old. What a difference that would make to our lives!
I was going to write a post with this title for New Year’s Day, playing on the New Year / New Leaf association by literally turning over leaves and showing what was underneath them. However, someone or something else intervened. The site crashed – I think it was hacked – on the New Year weekend and it took a few days to get it up again. (I think it is all back to normal now, but please do let me know if you spot any problems.) Meanwhile, however, most of the intended ‘New Leaf’ pics are already on my Flickr photostream, so I’ll just give you another photo of the odd mantis I described here a week ago. I turned over a leaf and saw the light shining through both leaf and mantis … but I had fun exaggerating the x-ray effect.
May 2012 be peaceful and happy for my readers and the wider world.
A month ago I wrote about finding a group of tiny just-emerged mantis nymphs. (‘Nymphs’ covers all stages of development except adults, from just-hatched to nearly fully developed.) In a footnote to that post I mentioned a larger nymph I discovered a little later. I have been observing and photographing that one and its relations (at least two more hatchings, all on a particular patch of weeds) since then and now have a reasonably complete record of their development.
First, the hatchlings (click on any photo for a larger image). They are quite different from the ones in my previous post. Most obviously, they are paler and have pairs of brown spots all the way along head and body. Also, their head is much broader than their thorax, and their typical posture is different: straddle-legged and straight-backed.
Mantises moult to move on to the next stage – the next ‘instar’ – of their development. The next stage I recognise is still completely wingless but the brown spots have faded. One or two instars later, wing buds appear; they have a faint mottling of darker green, as do the front legs. The nymphs are still straddle-legged but a new characteristic posture appears: they flatten themselves against the leaf they are on. They spend more time underneath their leaf than on top of it, at least by day.
Finally, the adult, about 20 mm long: the broad wings are translucent (note the leaf veins visible through them) and marked in a pattern of dark and light veining which resembles the pattern of the leaf itself. Around the ‘shoulder’ of each upper wing is a short row of yellowish spots, with minute black dots between them.
So what is it? Certainly a mantis (Mantodea, Mantidae) but not the common green Garden Mantid (Orthodera ministralis). It looks much more like the mantid shown here as Neomantis australis, but that one is still different in several ways: it has narrower wings, is more nearly transparent and yellower overall, and has dark eyes (which may be due to the fact that it is a photo of a dead insect). CSIRO’s (poor) photo of Neomantis australis shows an insect more like mine but with a transverse pale stripe across its wings, more like the one I saw on Hervey’s Range.
I suspect there are at least two species or sub-species amongst all these but for now I will just call my little family Neomantis australis with one or two question marks.