Friday, 5 February 2010

"Things are not always as they appear"

“Things are not always as they appear”. This was the admonition to DR from Mr James A. G. Rehn in the early 1960’s. Now what has dredged that up from memories long thought gone you say. Well my friend Jiva Sztraka, a local naturalist and computer expert, brought over the little katydid illustrated below stating that he hadn’t seen that species before. Well he probably has, but not in that form.


To get back to the original quote, Mr Rehn had been arguably the world’s leading orthopterist (a person who studies grasshoppers, katydids and their relatives) for over 50 years when he made the statement and admitted to a great error in judgement that he had hoped I would avoid.


Seems that one of his mentors, Dr T. D. A. Cockerell, prompted the young Rehn to describe as new a fantastic "katydid"the he had discovered. Mr Rehn told me repeatedly that he was reluctant to do so but Cockerell insisted and they produced a publication in 1903 in which the new genus and species Spilacris maculata Rehn & Cockerell was christened. Well, it turned out that it wasn’t a new genus at all but merely the early instar nymph of the very common American Fork-tailed Bush Katydid, Scudderia furcata fucifera Scudder. Mr Rehn was very embarrassed but wanted me to know that Cockerell pushed him into doing it. [Incidentally, they placed their new species in the wrong family!.]


Well what has this to do with Jiva’s katydid? We need to relate a little bit of taxonomy for those who do not know the situation in the katydid family. Katydids belong to the family Tettigoniidae, a very large group that has been divided by taxonomists into several subfamilies. The Bush Katydids are members of the subfamily Phaneropterinae. Jiva's find is a juvenile Bush Katydid. He found a juvenile (nymph) of a remarkable species that I was familiar with. I illustrated its life history in Grasshopper Country in 1996, plates 171-174.


Here’s how it goes. Upon hatching from an egg that the female lays on a twig or in a bark crack, the first instar (and there are at least 5 instars in this species before it’s an adult) mimics in colour and behaviour the Green Tree Ant, Oecophylla smaragdina. Lots of small insects mimic this ant, and with good reason. They are formidable and most vertebrate predators avoid them. Have a look at Densey Clyne’s book, noted below, and check out pages 36-37 and you’ll see what I mean. The little katydid not only looks like a Green Tree Ant but its behaviour is very ant-like. This fakery allows the baby katydid to seek a favourable habitat to begin its life. It is vulnerable and quite edible and non toxic but the disguise conceals all this. With each moult, the katydid grows, so after a time there is little reason to resemble a GTA. With each moult, the katydid grows. So with the second or third moult it resembles a slightly larger ant. Which one, I have no clue. Perhaps, no particular ant at all, but the behaviour is ant-like, or even wasp-like. Note the banded legs. As it grows larger, it moults and becomes greener, the banding on the legs disappears and after the last moult, a rather plain, green katydid with a short, black stripes on its forewing and reddish knees does little to reveal its past history. As an adult, the katydid is sedate and sits motionless on leaves in the tree tops during the day and feeds at night.


This is the first instar of the katydid species that Jiva found. Note the light green and brown colours, very similar to that of the Green Tree Ant.

The sequence below is the same individual that Jiva brought me a few weeks ago. It matured rather quickly and fed on a variety of herbaceous vegetation and flowers that I provided for it.

You can see the wing buds developing. Note the change in the colour and pattern.

Belive it or not, this is the adult. Note the absence of banding on the legs. The only real colour aside from the green is the short, black stripe on each side of the wing. Remember, this is the same individual that Jiva found.


Bush Katydids are notorious for this sort of outlandish fakery. A few examples are given below.
The Mountain Katydid, Acripeza reticulata Guerin, is a weird Bush Katydid. The young nymphs may resemble a beetle. When annoyed, they reveal a brightly coloured yellow neck membrane and exude a substance (toxic?) from the intersegmental membranes of the abdomen.


The early instars of Elephantodeta nobilis (Walker) resemble acacia flowers. This disguises them as they feed on the flowers and develop. As they mature, they lose the yellow colour and the adult is grey-green with little yellow at all. The eggs have to be in tune with the physiology of the plant. Otherwise if they were to hatch when the plant was not in flower, the very edible nymphs would be most vulnerable.


Pink nymphs of the Common Garden Kaytydid, Caedicia simplex (Walker), are not uncommon in Canberra gardens. They acquire the colour of the flowers on which they feed. At the last moult, the katydid become uniformly dark green and you would never believe they are the same species, let alone from the same individual.

So Mr Rehn’s admonition came to mind the minute I saw Jiva’s specimen. By the way, Grasshopper Country I identified that katydid as a species of the genus Polichne. But I am pretty certain it is not in that genus and it may actually represent an as yet undescribed genus and species. It is not uncommon around Kuranda and the Atherton Tablelands.


References

Clyne, D. 2010. All About Ants. (Young Reed Chatswood, New South Wales.) Pp. 1-48.

Rentz, D. C. F. 996. Grasshopper Country. The Abundant Orthopteroid Insects of Australia. (Sydney University Press, Sydney) Pp. 1-284.

Rehn, J.A.G. & Cockerell, T. D. A. A new genus of Stenopelmatinae (Orthoptera) from New Mexico. 1903. Proceedings of the Academy of Natural Sciences of Philadelphia, 55:630-631.

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