Dictyoptera (cockroaches and mantids)
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cockroach overview - cockroach egg case and eggs - cockroach amazing survival ability - cockroach body Cockroaches overviewCockroaches have been in existence for over 350 million years (since the Devonian).There are over 4000 species world wide, 130 species in Europe. 3 species are native to the British Isles, other cockroaches were introduced to the UK from warmer countries, probably arriving in cargo carried in ships. They are omnivorous scavengers and will eat almost anything (sometimes even cannibalistic), and active mainly at night. They are considered pests of stored produce because, although they eat only a little, they contaminate large quantities which take on a characteristic smell and have to be thrown away. Also they can be carriers of diseases spread by viruses and bacteria. They can be up tp 60 mm long, and their flattened bodies allow them to squeeze through cracks and hide in crevices. They are often mistaken for beetles, and the common cockroach (Blatta orientalis male left and female right), which was introduced to the UK in the 16th century, is also known as the blackbeetle. The adults are a shiny dark brown. The male has wings which reach about 2/3 of the way down his body (see left) and can fly. The female (above right) has tiny wing buds or lobes and is unable to fly. They are found everywhere except Antartica. |
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Cockroach egg case and eggsAbove left is a cockroach ootheca, or egg purse of Blatta orientalis showing how the eggs are arranged inside. There are usually around 16 eggs inside, and a female can lay up to 9 of these in her lifetime. When the eggs hatch they look like little worms, but very soon they moult to resemble a smaller version of the adult. The Nymphs moult 6 - 10 times before reaching adulthood. The female, above right is carrying her egg case. As with the Mantids the eggs are contained in an egg case or purse (ootheca) see the drawing above, and are carried around by the female attached to the tip of her abdomen for a few days before she deposits them; usually near a source of food. The ootheca contains from 16 to 40 eggs depending on the species. Cockroach amazing survival abiltyThey are hardy animals and the cockroaches that invade houses can survive for a month without food or water, two months on water alone, and 5 months on dry food. They can withstand a certain amount of freezing. 100 times the amount of radiation a human can endure. Humans lose consciousness at 12 gs (12 times the pull of gravity), but a cockroach can withstand 126 gs! Cockroach bodyThey have biting jaws and long, filamentous antennae. Those with fully formed wings can fly, but do so rarely. They have long legs and can run fast, and their cerci at the rear of the abdomen have hairs very sensitive to air movements making it very difficult to catch them from behind. |
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Above right is a diagram showing the arrangement of the internal organs of a female cockroach. In the German Cockroach, Blatella germanica, both sexes look alike, with the female being slightly larger. And both have wings reaching the end of the abdomen, also both sexes can fly. They have a dark brown body and are up to 16 mm long, and can eat almost anything. The eggs case holds 20 - 40 eggs, and a female can lay up to 7 cases in her lifetime, and need mate only once to do so. It is found world wide, but only indoors in the colder month in the UK. The saliva of the cockroach converts starches into glucose which can be absorbed by the crop. Gastric ceca produce a weak acidic fluid which emulsifies fats and converts albuminoids into peptones. This goes into the crop and is digested. The malphigian tubules are arranged in bundles, and there are usually around 70. They are excretory. The cells lining the tubules extract waste from the blood. On the right is a female Periplaneta americana, the American cockroach. The 7 th abdominal segment is shaped to allow the discharge of the large egg case (see above). It is found in sewage and kitchen worldwide. It has a raddish/brown body, and is up to 40 mm long. It can cause allergies and asthma in some people. |
| On the right are the mouthparts of the American cockroach, Periplaneta americana. |  |
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(C) 1997 - 2012 |
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