Green Tree Ants

Every northern gardener can tell you about Green Tree Ants. "They are pesky and numerous and get all over you when you try to garden". So true but when you look into them in a bit of detail, they are marvels of organisation.

The Green Tree Ant, Oecophylla smaragdina, in the same genus as the Weaver Ants of Africa. Our species is widespread in the tropics. Its geographical range includes northern Australia and much of tropical Asia.

We seldom see  GTA's in the rainforest because they are ants of the "edge" or of disturbed or open areas. You can usually find them on the vegetation of recently cleared areas or under power-lines where the vegetation is regularly cut and the habitat is more open. These ants are principally predators. They feed on other insects or whatever protein they can manage. I heard recently of an observation of hundreds of ants moving a small road-killed python up a tree to their nest where it would be dissembled and eaten.

Recently GTA's have been showing up at my light sheet. They work night and day removing any poor insect that takes their fancy. They do it in a systematic way. Once a prey has been selected, a group of ants stretches it out but they don't dissemble it. Instead they just hold it in that position for many minutes before taking it away. If you free the prey, you discover that it is dead. So how do they kill it? When the ants bite, they do not sting. When they bite us they often recurve the abdomen and squirt a small amount of formic acid in to the wound, just to make it more painful! But they do not seem to do this to potential prey. They just systematically hold it in a stretch.

When I consulted the "Ant Bible" I found numerous references to GTA's but nothing on their prey-capturing techniques.

This book is well worth having. It is 732 pages of fascinating information about the world of ants.

When the GTA's bite, they may inject a substance from their mandibular glands that renders the prey immobile. Or could the experience so shock the nervous system of the prey that is causes death? Someone may know the answer.

Here the ants have a female of a bibionid that is "protectively-coloured" meaning that it is advertising that it is distasteful to vertebrates like lizards and birds. However, this usually does not apply to other insects.

The GTA nest is a marvel in itself. They can be as large as a rugby football. This is a small one in the process of building. The ants tie leaves together in a community effort. They "sew" the leaves together with silk. But since the adults cannot do this themselves because they do not produce silk, they use their larvae for that purpose. A "string" of workers holds the leaves together while others come along bearing larvae that spin the silk that holds the leaves together to form chambers for the queen and brood.

The GTA's have a cadre of commensals that live with them and serve a variety of purposes. Butterfly caterpillars live within the nests affording them protection from predators and parasites. Their excretions provide the ants with sugars they need in their diets. The ants also "farm" in the sense that they promote and cultivate certain bugs like aphids and scales that also provide them with sugars for their diet. The ants no only protect their "cattle" from predators but they move them to better sites if they find them. So having GTA's in the garden because they consume pest insects is not always the case.

GTA's seem to be seasonal in our rainforest garden. We are in the midst of a very dry Dry Season and the forest has opened up a bit. Thus the ants. I suspect as the rains approach and the vegetation becomes a bit more dense, the GTA's will disappear and other more adapted rainforest species will take over.

The Big Parade

It's that time of year again. The moth season is about to commence.

Eustixis sp nr sapotearum; Lacturidae

Lyssa macleayi (Montrouzier); Uraniidae; Uraniinae

The Upside-down Day-flying Moth That Flies At Night

This large moth is fairly rare in north Queensland. It is said to be more common to the north where it occurs in New Guinea and Indonesia. Many uraniids are diurnal but this one in different. Oddly, it perches upside-down. The caterpillars are said to feed on Endospermum medullosum and probably other members of the plant family Euphorbiaceae.

 Hercules Moth, Coscinocera hercules (Miskin); Saturniidae; Saturniinae

I've noted this moth before, but they have just begun to show up at the lights after several months absence. This is one of the largest moths in the world and always attracts attention when it is seen for the first time. It also attracts the attention of the Black-butcher birds.

Caraea unipunctata (Bethune-Baker); Nolidae; Chloephorinae

Parotis sp., Crambidae; Pyraustinae

 Hypsidia erythropsalis Rothschild; Drepanidae

An old favourite, it is still difficult to believe that with such a large and beautiful moth, nothing is known of the larval stages nor of its host plant(s). 

 Artaxa sp.; Lymantriidae

 Donuca rubropicta (Butler); Noctuidae; Catocalinae

Caprina felderi Lederer; Crambidae; Pyraustinae

 Amerila timolis (Rothschild); Arctiidae; Arctiinae

 Eudocima aurantia (Moore); Noctuidae; Catocalinae

Chrysochloroma megaloptera (Lower); Geometridae; Geometrinae

 Tetrernia terminitis Meyrick; Crambidae; Acentropinae

(note the red mite on the top of the abdomen)

Acatapaustus mesoleuca (Lower); Nolidae; Nolinae

 Caterpillar of the Four O'clock Moth; Dysphania numana (Cramer); Geometridae; Geometrinae

Look carefully. See the tiny white spots. Those are eggs of a parasitic fly, probably in the family Tachinidae. The tachinid parasites are living within the caterpillar and will stay with it until it forms a cocoon. Then the caterpillar will die and the flies will emerge. This is a natural biological control. This exerts some form of control over the numbers of the caterpillars that will mature. But it is not a very effective way to preserve the host plant, Carallia brachiata (Rhizophoraceae). Most of the time, the large numbers of caterpillars devastate the plants.

Four o'clock Moth 

I'll end this blog with an unknown hoping one of the readers will be able to identify this moth. It appears to be an arctiid but it's one I have not seen before. There are always "unknowns" that act as the carrot before the jack-ass!

A Cold Night On Mt Baldy

It was a cold late winter's night with the wind blowing, trees creaking and mist blanketing the tree tops. We thought we were in for a poor night.

It seemed that not much was on offer.

A few dung beetles were at the ready:

But they had to be optimistic as we saw only a bandicoot. However, wild pigs had dug up the gutters of the dirt track looking for whatever they could find.

A few frogs were about

I suspect if was slim pickings for the frog population, especially those waiting on leaf surfaces.

Three cockroach species provided the interest for me. All are in the large and varied Australian endemic genus Johnrehnia. [The peculiar generic name is easily explained. It was named in honour of John W. H. Rehn, son of the famous Philadelphia entomologist, James A. G. Rehn. John studied cockroaches, especially their wing venation and how it relates to their classification.]

Two of the three species illustrated below were already known from Mt Baldy. The third was seen for the first time.

 Johnrehnia lakebarrina Roth was described from Lake Barrine, of course. The lake is not far from Mt Baldy. This attractive cockroach lives in leaf litter during the day but emerges after dark to feed on the bits and pieces of particulate matter that accumulates on leaf surfaces.

 Johnrehnia tibrogargana Roth was named for Mt Tibrogargan, one of the peaks in the Glasshouse Mountains of southern Queensland. It was a poor choice of names because even at the time it was described, it ws known from a number of localities along the coast and inland north to Cooktown. J. tibrogargana is common on leaves after dark but on this evening it seemed too cold for it to do much more than wander about in the leaf litter on the ground. On warmer evenings this cockroach is fast-moving and readily flies at the slightest disturbance.

Johnrehnia ruggi Roth was the find of the evening. This species was named in honour of Dr Doug Rugg, former student of Dr H. Rose, University of Sydney. This species appears to be restricted to leaf litter and does not ascend to feed on leaves after dark. That is probably why we had not seen it in the past. All that we saw wereon the ground and several were in cracks and did not appear to be interested moving much farther abroad.

 Johnrehnia species were placed in three species groups by Roth based on the shape of the male's subgenital plate. This is a distinctive structure used in cockroach taxonomy. Both J. tibrogargana and J. ruggi were placed in the Tibrogargana Group.

The subgenital plate consists of all sorts of gadgets having to do with copulation. Below we see the plate itself plus some of the internal structures comprising rods, hooks and the like. One of the neat things about cockroaches is that in many species their genitalia are not bilaterally symmetrical. This means that the left side is different from the right. So if a successful mating is to take place, the bits of the male must fit into specific counterparts in the female. If not, then a successful mating may not be achieved.

 J. tibrogargana, male subgenital plate, dorsal view. (Modified from Roth, 2000)

J. ruggi, male subgenital plate, dorsal view. (Modified from Roth, 2000)

Taxonomists use the shapes of the bits and pieces of the male subgenital plate to help identify species. There are many other features of a cockroach that are distinctive as well. But it is easy to see the differences in the two species above.

Tibrogargana Group species, and there are five of them, have the hind margin of the plate complex with the corners with setal and spine-like structures. In addition, the subgenital plate is not flat but subcylindrical. Here is is illustrated and flattened out.

J. lakebarrina male subgenital plate, dorsal view. (Modified from Roth, 2000)

It is easy to see the differences in the subgenital plate of this species when compared to the two above. It is a member of the Hodgkini Group along with more than twenty other species. This group is distinctive in that its species have the hind margin of the plate simple with the right and left styles (the appendages in the middle) dissimilar, the left one being small and cylindrical. In addition, the plate lies flat and is not subcylindrical.

So there is more to a cockroach than most people realise. They are complex and interesting organisms that have been around long before the dinosaurs. Australia has a remarkably large fauna of these insects. Only a half dozen species cause problems. All of the others (over 500 in Australia!) are at home in their habitats which do not include human dwellings. They are extremely common, especially in forests. They must be very important in the decomposition of leaf litter and the ultimate health of most habitats. Many are very colourful and attractive. You will be seeing more of these in the future!

Literature

Roth, LM. 2000. The Australian cockroach genus Johnrehnia Princis (Blattellidae; Blattellinae) Oriental Insects, 34: 83-192.