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Bush crickets - the creeps or fascination?

Avatar of inke inke 22. September 2017 - Discover Namibia, Environment

Towards the end of their life of just a few months armoured crickets, Acanthoplus discoidalis in this picture, feed on their own injured or dead kind and on other protein.

In some years thousands of armoured bush crickets are run over on Namibia’s arterial roads at the end of the rainy season, when winter is on its way. The spiky, almost black insects are about three centimetres long and occur only during the summer months. One of their defence mechanisms is to squirt their yellow blood. Many people find them disgusting. Colloquially this cricket is referred to as dickpens (Afrikaans for fat stomach).

According to Eugene Marais, the curator and entomologist at the National Museum, five species of long-legged armoured bush crickets are found in Namibia. If conditions are favourable for them, Acanthoplus discoidalis and Acanthopus longipes can be seen in their thousands: the former in the central and northern parts of the country, the latter in the southern and western parts. The less common species Acanthoproctus diadematus is endemic to some parts of the Namib Desert, while Acanthoproctus cervinus occurs in the southern, central and northern fringe areas of the Namib. Number five, Hetrodes pupus namaqua, is only found in the south of the country.

Armoured bush crickets hatch at the start of the rainy season. At that stage they are green and measure just a few millimetres. They shed their skin seven times before they are fully grown. During this phase the voracious young insects devour only plants of any kind. Later, when they mate, they look for more protein – in particular the females ready to deposit their eggs. That is the time, at the end of the rainy season and the start of winter, when armoured crickets are found feeding on carcasses and especially on their own kind, killed or injured on the roads. Then it’s cannibalism à la carte. 

It is also the time when male crickets start chirping late in the afternoon to attract females. Mating usually takes place at night. The male transfers to the female a sperm packet in a protein mass which tightens as it dries and thereby pushes the sperm into the female body. At sunrise, in the early morning hours which are already chilly at that time of the year, female crickets can be seen eating the protein mass that remained on their abdomen.

Marais explains that each female deposits some 20 to 30 eggs in the ground. Even under the most favourable conditions not a single tiny insect will hatch during the first six months. This ensures that the eggs will survive the winter. If it then happens that a shower of 5 to 10 millimetres comes down at the start of the next rainy season, just a few crickets will hatch from the egg parcel. If it immediately rains 20 to 30 mm, most of the 20 to 30 eggs will hatch. In the case of 40 mm and more, all the young armoured crickets see the light of day. This is the reason why these insects are seen in their hundreds of thousands in some years, while in others just a few or none of them are found. Eggs can survive in the ground for at least eight years. The crickets hatch only when conditions are favourable and the first rain is sufficient. 

Among the few animals that eat armoured crickets are black-backed jackal, bat-eared fox, kori and Ludwig’s bustard, guinea fowl and hornbill. Especially Monteiro's hornbill, which is endemic to Namibia, thrives on the crickets and feeds them to its young. This hornbill species starts its breeding process as soon as the armoured crickets have shed their skin for the third time. Armoured crickets live for only one summer. Adult crickets die after mating and depositing the eggs.

Dirk Heinrich

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