The Peppermint Stick-insect

Tis the Season. So why not the Peppermint Stick-insect. It is unlike the traditional peppermint stick in that it is not red and white. Here is its story.

Click on the photos to enlarge

Typical resting position of a female Peppermint Stick in the mid-rib of Pandanus.

The Peppermint Stick-insect, Megacrania batesii (Kirby 1896) Phasmatidae; Platycraninae is one of the insect icons of the Daintree Rainforest region of far north coastal Queensland, Australia. Tourist operators know of at least two populations that provide impressive displays.

The fore and middle legs are forward with the antennae in between. Not the short forewings.

Although described over 100 years ago, these insects went unnoticed until relatively recently. My predecessor at CSIRO, Ken Key, showed me some ancient specimens in the collection from islands in the Gulf of Carpentaria but he said he had heard that the species was in the Daintree region in the far north. But nothing was known of its habits so it was with great excitement in the early '90's that I found a population in the Cape Tribulation area. I learned later that Jack Hasenpusch knew of a population at Etty Bay.

Resting in the heart of a spiny Pandanus. Note the feeding damage in the foreground. It would be a brave bird or lizard that would attempt to extract this individual.

This stick insect is associated with Pandanus. There are several species of Pandanus but this insect seems to prefer only one, P. tectarius. P. tectarius has a very broad distribution occurring along the the coast and inland for a considerable distance. So it was logical to assume that the sticks could be found elsewhere. But this is not the case. Diligent searching for many years of every Pandanus has failed to locate additional populations of the species. Where these insects occur they are numerous and the plants they live in have a distinct appearance. The leaves are chewed to the mid-rid in characteristic semicircular patterns.

"Paired up" The female is the larger individual on the bottom. This is a large insect, roughly the length of a pencil and slightly broader. Note that the pair is not mating. Males seem to "stake out" females and ride around on their backs. They are therefore available for mating whenever. Behaviourists would suggest that the male is therefore, protecting his offspring from being cuckold by other males. 

A pair of Peppermint Sticks. Note they are not attached.

The sticks have a rather simple biology. They never stray from their host plants even though they are winged and could probably fly or at least glide a bit. This species was described originally from the Solomon Islands and New Guinea and the Bismarck Archipelago. That may give some clue to the distribution of the stick.

The sticks live in the mid-rib of the Pandanus leaf. They scuttle back and forth and are highly perceptive of external activities. As soon as they detect the presence of danger, they retreat backwards into the base of the leaf protected from intruders by the spiny hooks along the sides of the leaves. They move using the fore and middle legs and use the hind legs only to move from one leaf to the other.

The droppings (frass) accumulates in the base of the leaves along with the many eggs females produce. During cyclones masses of Pandanus get dislodged and float out to sea. The sticks probably die during this time but the eggs may be safely carried to a new destination tucked in the axils of the leaves.

Frass accumulated inside at the base of the pandanus leaves. It is early in the season so there are few or no eggs there at this time.

An additional advantage to the stick is that it is probably facultatively parthenogenetic. That means that unmated females can lay eggs that hatch. In fact, it seems to be the case that the populations south of the Daintree region. Apparently no males have been found in these populations.

A late instar nymph, more blue than green.

A last instar female nymph. +Note the developing wing buds of the fore and hind wings. Also note the feeding damage to the plant.

Peppermint Sticks are diurnal. They have well developed eyes and are well aware of their surroundings. When suitably threatened, they squirt a white milky substance from the corners of the thorax at the intruders. The smell is reminiscent of peppermint. Hence the name!

A disturbed individual. The white spots are the points where the peppermint-smelling fluid is exuded as a spray. 

Seasons Greetings from the Peppermint Sticks and Bunyipco.

A Couple of Rainforest Pretties

Not all insects you see in rainforests are stunning but here are a couple that are really excetional.

 Zeuzera aeglospila (Turner) is a member of the family Cossidae. Cossid are called Carpenter Moths because the larvae live in dead wood, feeding and reducing the wood to phrass that provides nutrients to plants and other organisms. Z. aeglospila is a Queensland species but another member of the genus occurs in India and the Philippines feeds on Cinnamon trees and the genus Litsea. Nothing is known of the habits of the Australian species but we have Litsea on our property.

Many of the Carpenter Moths are grey or brown, not very colourful. But when you see this species up close it has a remarkable array of colours and iridescence.

Another gem is the Cuckoo Wasp. There are many species spread throughout the world. As a rule they are a challenge to the photographer because they seem like perpetual motion machines. You often see them examining holes in wooden buildings in search of potential hosts.

This little fellow flew into the house and landed on the window sill where it gradually came to rest.

Cuckoo Wasps (family Chrysididae) are usually under 20 mm in length and have a tough integument. The punctured sculpturing is a characteristic of the family and probably aids in preventing them from being stung. Most are parasites of other wasps ands when the tables are turned, they can roll up into a ball and become almost impervious to the stings of their hosts. A few species are parasites of moth larvae.

Young of the Year

It's that time of year again. The Black Butcherbirds, Craticus quoyi,  have fledged their young. This year there are two juveniles that will be raiding nests and creating havoc in the local animal community.
[Juvenile Black Butcherbirds are brown. Why? Who knows?]

These two have discovered that there are easy picking early in the morning at the light sheet. Large bitey long-horned beetles offer little resistance.

The hooked tip of the bill is ideal for catching and holding prey. Unfortunately, their depredations don't end with insects. They are major predators of the young of Sunbirds. They await the time when the young birds fledge and they capture them on their first flight.

Butcherbirds redeem themselves with their melodic and beautiful calls. They are a wonderful feature of the fantastic down chorus in the rainforest and environs. This species extends north to New Guinea.

A Real Cutie

For the past couple of weeks this little Long-nosed Bandicoot, Perameles nasuta, has been a regular evening visitor to my lightsheet. It seems to be a juvenile because it is so small and generally unafraid.

It crunches up beetles, moths and other insects that drop to the ground at night.

Bandicoots are nocturnal and are marsupials. Females have a small pouch that is directed towards the rear of the animal and produce young after a gestation period of only 12 days. Newborn young are only 13 mm long and weigh 0.25 g. They grow rapidly and are weaned after 60 days.

When not dining at entomological collecting sites, the bandicoots use their front feet to dig neat conical holes in woodlands and lawns to retrieve insects, worms etc. They are not very popular with gardeners  and greens keepers.

Unfortunately, they are popular with the local felines. Cats probably account for their demise in residential areas. We have a number of irresponsible neighbours that throw their cats out after dark. Hopefully the local pythons and paralytic ticks will read this a do something about the situation.

A Gynandromorph: This is a case where Arthur is Martha!

This appears to be a rather typical-looking Raspy Cricket. Raspy Crickets are members of the family Gryllacrididae. They are crickets but very different from the average field cricket one is familiar with. These crickets have the ability to spin silk with their mouthparts. They do this to construct enclosures where they spend the day. They tie leaves together or construct underground burrows that are stabilised with webbing. They even  provide the burrows with a cap that keeps them sealed in a waterproof and predator-proof enclosure when danger threatens. Perhaps, the most important feature of an underground burrow in the desert is to reduce the problem of water loss through evaporation.

What is interesting about this cricket is that it is a gynandromorph, that is, it is a creature that possesses both male and female characteristics. As an entomologist involved with fieldwork for over 60 years, I guess that I have come across fewer than a half dozen insects illustrating this phenomenon. The most spectacular are those that are bilateral, that is, where half the insect is male and the other half is female. Butterflies illustrate this best and can be very spectacular. But not all gynandromorphs are bilateral. The most usual cause for this malady is an "event" early in life at mitosis when cells are dividing and the chromosomes are recombining. Gynandromorphism probably leaves the individual sterile and unable to reproduce.

This cricket is not a true bilateral gynandromorph. It probably fits into the "oblique category as will be seen below.

Viewing the top of the head and pronotum, one can see nothing amiss. Everything appears normal. Similarly, a frontal view conveys a normal gryllacrdid appearance.

Gryllacridids are not known for outward sexual dimorphism except genitalically. In this respect they are truly spectacular, especially in males. The male genitalia displays an intricate array of hooks, claspers and modifications that provide examples of the old "lock and key theory", that is, the male genitalia are of a morphology that they will only work in females that of the same species. This theory has been challenged over the years but it is useful to make a point. In all the gryllacridids that I have examined, the male and female genitalia are highly distinctive. As a result they are the most useful taxonomic characters.

In more typical crickets (family Gryllidae) where males produce song, the wings are structurally modified for sound production. Gryllacridids also produce sound but in a different way. Individuals of both sexes in all stages of development can produce rasping sounds--hence the common name. Both sexes also "rasp" during courtship. 

They produce rasping sounds by inflating the abdomen slightly and rubbing pegs on the abdominal segments against a raised series of minute bead-like projections found on the inside of the adjacent hind femur. Other related families produce sounds in that same way.

 In this specimen the line of pegs are on the first and second abdominal segments. These pegs are actually modified hairs. They are at least generically characteristic and many were reviewed in several Australian genera by Rentz and John (1990). 

The pegs up close.

The inside of the hind femur.

A close-up of the bead-like structures that are rubbed against the pegs on the adjacent abdomen. 

Back to the odd features displayed by this cricket.

This individual has a part of an ovipositor. The normal ovipositor has two main parts that are divided down the middle. In this specimen we see the right side of what appears to be the right half of the ovipositor. Gryllacridid ovipositors are normally straight and long, about half the length of the insect itself or even longer in some species. Since this cricket had to undergo several moults in becoming and adult, it appears that the ovipositor did not develop properly and part was lost or broken after moulting.

This shows that there is just a half an ovipositor. The left half is missing. 

The V-shaped plate at the base of the ovipositor is the subgenital plate. this strucutre is normally sexually dimorphic and if this were a true bilateral gynandromorph, each side would have a very different structure. But here it appears symmetrical.  Note the little brown sclerite at the base of the filamentous cercus on the right.

These photos show the abdomen from above. The ovipositor is deformed, the right half which is twisted and pointed to the left. The white fleshy bits are usually possessed by males, females have a more sclerotised tip of the abdomen. This is unusual in this example. The small sclerite on the right at the base of the cercus may be a significant part of the normal male genitalia and the black ridge on the left is a feature found in males of some species. 

This is a most unusual gynandromorph. The internal morphology would show testes on one side and ovaries on the other if this were a bilateral gynandromorph. These features have not yet been examined on this specimen.

But what genus and species is this cricket? Based on the arrangement of the pegs on the abdomen, I would place it in Mooracra. Should we find additional specimens at this locality, we can provide a more authoritative identification.

There is a remote chance that his cricket is not a gynandromorph at all. It's deformity may be from some other cause such as parasitism. If so, this is the first time I have found such an anomaly.

Reference
Rentz, DCF, John, B. 1997. Studies in Australian Gryllacrididae: Taxonomy, biology, ecology. and cytology. Invertebrate Taxonomy, 3: 1053-1210. 

The Irresistible Force is An Immoveable Object!

Leptopius malefictus (Lea)

This weevil spent the better part of a day perched on a balcony rail. It was the constant source of attention to passing Green Tree Ants (Oecophylla smaragdina).

Something conveyed to the ants that this was a potential food item, but try as they might, they could not budge the weevil nor gain entry to any of its soft bits.

We have dealt with this before in this blog with pesty Orchid Weevils unable to be overcome by interested jumping spiders. Anyone who has tried to pin a weevil for an insect collection will be aware at just how hard the integument is. Inserting a pin into some of the larger species is almost impossible. This toughness seems to afford protection from small predators.

One might expect the head to have some soft bits where the ants could gain a purchase but no. Even the antennae were rigid and tough. It seems the only soft parts exposed by the weevil are the tarsi. These were completely ignored by the ants.

The weevil remained in its "staid" position all day but was gone overnight. The ants are primarily diurnal in their activities!

The Recent Cacophony

Cephalogryllus tau calling song a video by orthop1 on Flickr.

The cricket producing this intensive sound was about 25 cm (10 inches) from the microphone. It is Cephalogryllus tau Alexander & Otte, a member of the Gryllidae; subfamily Gryllinae. The sound is ear-piercing, even to these old ears when up close. The crickets seemed randomly spaced but fairly close together. The background sounds are largely of this species. The beeps towards the end of the recording are of a small frog.

The antennae are extended from the burrow and wave back and forth. The short-winged cricket is adapted for a tight burrow. Long wings would require a larger burrow and that might lead to a greater array of predators like bandicoots and geckos.

During the day, the burrows are closed by the crickets and are reopened after dark if the night is suitably humid.

Why do the crickets sing? Well it is widely agreed that crickets sing for several reasons. The most common reason is the sounds are specifically designed to attract mates. Males produce the call. However, territorial or aggressive calls have been observed in many crickets. Since C. tau is a relatively recent discovery, nothing is known of its biology other than it lives in burrows. In this genus the females are very short-winged, the tegmina only about 1/3 the length of the pronotum. They produce no sounds. Presumably, the females wander about on the surface of the ground seeking singing mates. However, no females were observed on the evening the recording was made.

Some mention should be made of how crickets produce song. Almost all crickets and katydids produce sound by rubbing their wings together and that is almost the exclusive domain of males. In katydids it is usually the left wing (tegmen) that is rubbed over the right. In crickets, for some reason, it is the right that is rubbed over the left. Sounds produced in this way are called stridulations. This is called the file and scraper method. The analogy is similar to running your thumbnail across the teeth of a comb.

The loud sound produced by G. tau is surprising considering the short, stumpy size of the wings themselves.