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November 2003

Feature

 


The monstrous cricket "turns 200" while "badboy"  Parktown prawn steals the limelight


Dr Rob Toms

The Parktown Prawn is South Africa's most famous king cricket. However, the 'Monstrous Cricket', described 200 years ago is an even more spectacular animal. To find out more about these exciting and unusual animals and the controversies surrounding them read on. Did Parktown Prawns come from space or Barberton - which is scarier? Do King crickets sing love songs at night? Rob Toms sheds light on these interesting topics.

Henicus monstrus. Pic from www.museums.org.za 2003 is the bicentenary of the description of the "monstrous cricket" Henicus monstrosus (Herbst), from the Western Cape province of South Africa by Herbst back in 1803. This was also the first king cricket (Anostostomatidae) ever described. King crickets are best known in south Africa as relatives of the "Parktown Prawn", Libanasidus vittatus.  Forty four species of king cricket have already been described from South Africa and there are many more that need to be described.

During the 19th century and early 20th century Henicus monstrosus was probably South Africa's best known king cricket, and was the only species discussed by Skaife in the 1953 version of African Insect Life. This species has now undoubtedly lost its position as the best known species in southern Africa to the "Parktown Prawn".

Love songs for the big headSketch of a monstrous cricket's face. By Elaine Taylored monstrous cricket

The most remarkable feature of H. monstrosus is the face of the males, which is unusual even amongst other king crickets. It is thought that the large round face may be used to plug the entrance of their burrows as the males wait for passing females, intruders or prey. The function of the two lateral horns on the face of H. monstrosus and other species of Henicus is not known and field observations of these insects are needed. 

According to Skaife, male Henicus monstrosus make a rasping noise by rubbing their mandibles and maxillae together and it has been suggested that this gnashing of the teeth constitutes a love song.  

This is interesting because most Anostostomatidae have the ability to hear and most males can produce sounds, so well developed acoustic communication is possible. However, most species of king crickets produce rather soft sounds, and it appears that these may be important in courtship and defence, but are not known to be important in calling or attracting females. If it is true that H. monstrosus sings with its mouthparts, this would act as another good example of the independent evolution of sound producing mechanisms which have evolved independently several times in Anostostomatidae. Unfortunately, the stridulatory behaviour of these insects has not been adequately studied and no recordings of their songs are available. 

Examination of one male in the collection of the Transvaal Museum revealed that the ears are degenerate and that external tympana are wanting. Lateral abdominal stridulatory pads are also wanting in this species. Scattered lateral abdominal spines may be indicative of the morphology of ancestors of species that subsequently acquired well developed lateral abdominal stridulatory pads. Alternatively, they may represent degenerate stridulatory pads. The femora of this species are smooth, but it is not known whether this condition is primitive or advanced. The mouth parts could be used for stridulation but further examination is necessary. 

Although Henicus monstrosus was described two centuries ago, we still know very little about its biology or behaviour. The genus Henicus is distributed along the mountains of the Western and Eastern Cape.

The troubles of the scientist - missing information

The monstrous cricket - sketch by Elaine Taylor.

The monstrous cricket

Toms discovered that the primary type specimen (holotype) is supposed to be at the Oxford University museum, according to information on the Orthoptera Species File. However, the holotype could not be found at this museum or anywhere else and remains missing. "We eventually located an incomplete copy of the original description, now kept on microfishe," he says.

Unfortunately, when the original reference was transferred to microfishe the diagrams were not included so there is no complete copy of the original description available. It was also found that in the original description there was no record of the locality at which the holotype was collected. 

The early descriptive work on South African insects was invariably done using small sample sizes of specimens (often = 1), collected under very difficult conditions which may have included encounters with various large mammals. The knowledge of the African fauna was strongly affected by these constraints. Most of the early work was done on specimens that were sent to various countries in Europe. Given the rudimentary communication systems that existed until about fifty years ago, many synonyms were described by biologists who were not always aware what their colleagues at other institutions and on different continents were doing. The fact that these insects are sexually dimorphic, together with the fact that new species were frequently described on the basis of a single specimen made it especially difficult to compare species, especially if they were described on the basis of single specimens of the opposite sex. 

Many nomenclatural problems and synonymies have been sorted out over the last century, but some of these have only just been resolved.This means that it is now possible to move forward with a far firmer footing, with most of the basic nomenclatural problems resolved.

The now  famous (or infamous) Parktown Prawn

By far the best known king cricket species in South Africa is Libanasidus vittatus, otherwise known as the Parktown Prawn, a reference to the fact that they often stumble into swimming pools in the affluent suburbs of Johannesburg, South Africa. The natural habitat for this genus is in and around forests in Mpumalanga, Northern Province and probably also Zimbabwe. During the day they can be found in burrows or under logs. Specimens have also been collected in gardens in Johannesburg, Randburg and Pretoria. A few articles have been written on the biology these insects, but very little is known about any other species of African king crickets.

The "Parktown Parwn". Sketch by Elaine Taylor.
The "Parktown Prawn"

The "Parktown Prawn" has captured the imagination of the general public living in Johannesburg and surrounding areas to such an extent that it has stimulated numerous articles in the local and international media, and has featured in publications such as Time and The Economist and has appeared on BBC and CNN International news broadcasts. They are also popular subjects for school projects. This species already has its own website, and two rampant Parktown Prawns have featured on a billboard advertising a local radio station.

One of the largest females researched, collected in indigenous forest in the Soutpansberg Mountains in the Northern Province, measures 64 millimetres from the front of its head to the tip of its ovipositor. The ovipositor is 19 millimetres long and the total length of the insect, including legs and antennae, is 166 millimetres (six and a half inches). South African Jerusalem Crickets (Stenopelmatidae) in the genus Sia (formerly Maxentius) may be even larger than the large African King Crickets such as Libanasidus. A male Jerusalem Cricket may measure up to 250 millimetres including legs and antennae (body length = 63 mm; abdominal width = 22 mm), but these insects do not have a strong association with people, so few people know that they exist.

Please get out of my bed

Many people dislike or fear the "prawn" as they frequently wander into houses, where they may even appear inside peoples beds at night. One of their least liked attributes is their defence mechanisms of jumping when they are molested, often coming to rest on the clothing of a person who disturbed them or a bystander. People have been known to move house to get away from them, and one person slept in her car to avoid being surprised by them at night.

A male "Parktown Prawn", Libanasidus vittatus.This species has featured in several myths, mostly related to their sudden prominence in Johannesburg in the 1960's. For example, it has been suggested that they are alien invaders, or the result of some kind of freak mutation. Fortunately, sufficient collecting of these creatures was done before these rumours emerged, so it is possible to respond to them with the advantage of historical museum specimens. The fact that this species was described from a specimen collected by P. Rendall in Barberton (Mpumalanga Province, South Africa) more than 100 years ago is sufficient proof that this species did not suddenly appear 30 years ago.

From space or Barberton?

Until about 1965 the "prawn" was almost unknown in Johannesburg, but then the populations increased for some unknown reason, and they started to become notorious. In 1985 it was suggested that they could have been introduced into Johannesburg from somewhere near Barberton, but we now know that these insects were already present in Pretoria in January 1955, because there is a specimen in the Transvaal Museum, collected by George van Son, who was Curator of Entomology at the time. 

The first museum specimen from Johannesburg was collected by R. du Preez in November 1962. It now seems possible that they were originally present in low numbers and that environmental changes in suburban gardens led to an increase in numbers and range. However, urbanization may not have been the only reason for an increase in numbers, and changes in weather patterns may also have played a role. When the rainfall increased over the past three summers it was expected that this would lead to a massive increase in populations, but surprisingly, the opposite occurred. It is thought that flooding of burrows and refuges could have led to a decline in populations. Unfortunately entomologists do not have quantitative data associated with changes in population density, but it is possible that this species could act as environmental indicators. 

Modern technology, permitting techniques such as DNA and protein analysis, could help us to determine whether these insects were introduced into Johannesburg from somewhere like Barberton, or whether a small local population underwent an increase in range and numbers.

Parktown prawn educates the public

Since there is great interest in these insects there is also a great opportunity for public education by making appropriate information available. One opportunity for public awareness was the centenary of the description of L. vittatus in 1999. When the idea of celebrating the centenary of the Parktown Prawn was first suggested, some people thought this was a joke, but even this was part of the process of attracting attention. Once one has an audience, the opportunity exists to provide information about crucial issues in museology and biodiversity. Issues such as the biodiversity crisis, the age of collections and the need to collect and care for specimens, declining funding and even repatriation can be addressed (the Holotype or primary specimen of the Parktown Prawn is an adult female collected in Barberton and housed in the British Museum -Natural History). It is thought that this is the first time that the centenary of any insect has been celebrated.

Smelly self- defence and a bit of karate

Recent research on the behaviour of these insects has revealed that their vile smelling faeces, which may be ejected in self defence, plays a role in intersexual communication and territorial behaviour. Males and females are able to discriminate between faeces produced by members of the same and opposite sex, and can use these cues to find conspecifics of the opposite sex or avoid confrontation with members of the same sex. Mating behaviour, mate guarding and male-male relative strength has also been studied in these.

One of the most interesting features of the morphology of these insects is the anterior mandibular tusks. The tusks of Libanasidus arise as an anterior outgrowth of the mandibles. These tusks are similar to those of New Zealand tusked weta, as both are outgrowths of the mandibles. Libanasidus and tusked weta both exhibit advanced mandibular development in contrast to the undeveloped mandibles of Borborothus and simple development of mandibles found in genera such as Nasidius where the mandibles are simply elongated and thickened. It is suggested that these mandibles arose from small protrusions on the mandibles of ancestral species, which may have resembled those found in Libanasa. Male Libanasidus vittatus are known to use their mandibles during digging of their burrows, where they are able to shift sand with an action rather like that of a bulldozer. They have also been observed using their strong mandibles in disputes with other males by gripping their opponent and throwing him over their back.

Very little is known about the stridulatory mechanisms of African Anostostomatidae. Sound production in Libanasidus is similar to that of many New Zealand weta, where the males stridulate by rubbing the lateral abdominal stridulatory pads against the modified inner surfaces of the femora. Stridulation is known to occur during courtship and in self defence. Tibial ears are clearly visible on the front legs, and this is an important derived feature shared with the Gryllidae and Tettigoniidae, but not with Stenopelmatidae (sensu stricto). Thus, it is possible that Gryllidae and Tettigoniidae evolved from winged anostostomatid like ancestors that already had tibial ears.

Juveniles in various stages of development can be dug up during winter, so it is thought that the most important way of overwintering is as juveniles. Adult insects seem to die at the beginning of winter so overwintering may also occur in the egg stage. Females deposit up to 200 eggs in damp soil by thrusting their long scimitar shaped ovipositor into the soil repeatedly, apparently laying just one egg each time. The omnivorous diet of these insects is known to include garden pests such as slugs, snails and cutworms, so they can be regarded as beneficial allies.

Back to the future

Although certain genera and species are now fairly well represented in collections, there are regions where little or no collecting has been done. When the weather conditions are not optimal (usually too dry) king crickets may be difficult to collect and the sample sizes of specimens collected may be small. Most of the collecting done now is aimed at opportunistic collecting of all Orthoptera in areas where specific goals can be achieved. Unfortunately, opportunistic collecting of these insects is badly affected by dry weather because they tend to hide. The roads and infrastructure in South Africa are of the best in Africa, but there may be interference from people in some areas. In the large national parks one may encounter large mammals, and the nocturnal habits of king crickets makes it necessary to work at night. Under these conditions collecting is generally done close to a vehicle after the general area has been checked with good lights. Some parts of Africa such as Angola and Mocambique have been extremely poorly collected because of human activity.

African Anostostomatidae are interesting insects and there is huge public interest in them. Hopefully these positive factors can be used to counteract difficult collecting conditions and limited employment and funding opportunities so that we can lean more about the many species which are poorly known or completely unknown.


More information:

This article quotes extensively from Toms, R.B. (2001). South African King Crickets (Anostostomatidae). In: Field, L.H. 2001. The biology of Wetas, King Crickets and their allies. CABI publishing. 540 pp.

The Original description of Henicus monstrosus was in:
Herbst, I.F.W. (1803) BeschreiBung einiger hochst seltener Heuschrecken. Neue Schriften der Naturforschender Freunde zu Berlin 4, 111-120, tf 1, figs 1-5.
If anyone happens to have a clean copy of this reference with the figures it would be most appreciated!

All diagrams by Elaine Taylor

Dr Rob Toms is with the Department of Ethno-ecology, Transvaal Museum, Northern Flagship Institution, PO Box 413, Pretoria, 0001 South Africa. Toms@tm.up.ac.za

 

 

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