Dictyoptera (cockroaches and mantids)

Dictyoptera fast facts

  • Large or medium sized insects.
  • They can be separated into two sub orders, Blattodea (cockroaches), and Mantodea (mantids). Some books include the Isoptera (termites) in this order.
  • They have two pairs of wings, but the front pair is leathery and held flat over the body when at rest.
  • The antennae are long, and may be longer than the entire body length.
  • Cerci (two small appendages sticking out of the rear of the insect) are visible, and the hairs on the cercus are very sensitive to air movement in cockroaches, which explains why it is almost impossible to catch them.
  • Biting mouthparts.
  • Females lay their eggs in batches in hard-walled capsules or oothecae.
  • Cockroaches: about 4000 species worldwide, 150 in Europe, 9 in British Isles, but only 3 are native, and these 3 are small and harmless.
  • Mainly nocturnal and omnivorous.
  • Mantids: about 2000 species worldwide, mainly tropical about 35 species reach Southern Europe.
  • Mantid size ranges from 1 - 15 cm long.
cockroach malecockroach egg casecockroach female carrying egg case

Cockroaches overview

Cockroaches have been in existence for over 350 million years (since the Devonian), and have changed very little over the years. Fossilized cockroaches from 250 million years ago look very much the same as cockroaches today.

They are omnivorous scavengers and will eat almost anything (sometimes even each other), and are active mainly at night. They are found in a wide variety of habitats. Fewer than 1% of cockroach species are "pest" species; in fact only around 25 - 30 are considered pests, and of these only 4 or 5 are global pests.

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.

Cockroaches range in size from just a few millimetres to over 100 mm in length, and their flattened bodies allow them to squeeze through cracks and hide in crevices. Most are dark brown, but black, tan and other colour variations do exist. Most have 4 wings in the adult stage, and some are capable of long and rapid flight. Other species are wingless or have reduced wings. They are often mistaken for beetles.

The common cockroach, Blatta orientalis

The common cockroach (Blatta orientalis male and female left), which was introduced to the UK in the 16th century, is also known as the blackbeetle. It is probably the 2nd most important pest cockroach. The adults are a shiny dark brown. The male has wings which reach about 2/3 of the way down his body (see above left) and can fly. The female (right) has tiny wing buds or lobes and is unable to fly. They are around 20-27 mm long, and as their common name suggests, are black or dark brown at all stages in their lives. They are found everywhere except Antarctica, but is most common in the temperate regions of the world. They are often found outdoors, in basements and in colder areas of buildings. Their lifecycle takes 1 - 2 years.

Cockroach egg case and eggs

Above 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 ability

They 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.

They can survive 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 body

They 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.

On the right is a diagram showing the arrangement of the internal organs of a female cockroach.

The German cockroach, Blatella orientalis

The German cockroach is probably the most important pest cockroach, and it is found worldwide. 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.

internal organs of a cockroach
, female, ventral surface

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. They are found world wide, but only indoors in the colder months 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 left 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).

Periplaneta americana, the American cockroach

The American cockroach is the 3rd most important pest species. It measures 35 - 40 mm long, and is chocolate brown in colour. Both sexes have wings, and both can fly, but their flight is weak. They are found world wide. Their lifecycle take 6 - 9 months to complete. Despite its name it is believed to have originated in Africa.

It is found in sewage and kitchens worldwide. It can cause allergies and asthma in some people.

Below are the mouthparts of the American cockroach, Periplaneta americana.

Cockroaches and human health

Cockroaches themselves do not transmit diseases to humans, however because of their habit of feeding on almost any type of organic matter they can harbour many kinds of pathogenic and harmful organisms both in and on their bodies. It is these harmful organisms that cause diseases, and they can remain viable on and in the cockroach for a considerable period of time. So when the cockroach feeds or soils food that is subsequently consumed by humans these harmful bacteria and other organisms are spread to us. In this way intestinal infections such as gastroenteritis, diarrhea etc. can be spread by cockroach activity.

Some of the better known bacteria found in or on cockroaches includes, Shigella, Staphylococcus, Salmonella, Escherichia, Streptococcus, and Clostridium.

Protozoa found in/on cockroaches includes Entamoeba, Giardia, and Toxoplasma.

Parasites include, Schistosoma, Taenia and Ascaris.

This list shows that cockroaches can be vectors of a large number of diseases. Humans can also build up an allergic reaction when under constant exposure to cockroaches. This usually manifests itself on the skin or in the respiratory system. The German and American cockroaches are the most commonly involved in producing these allergic reactions.

Cockroach control

The most important word to understand here is "control". Eradication will not happen. They were here a long time before us, and will most likely still be here long after all traces of us have gone.

Basic cleanliness and lack of clutter is and always has been the best control. This will deprive the cockroach of feeding opportunities and hiding places. Non-chemical controls consist mainly of trapping them on sticky traps and vacuuming them up. These methods are easy, fairly economical and effective in keeping infestations small. Other non-chemical controls include freezing, overheating and even flooding structures with a non-toxic gas. Chemical controls use insecticides in aerosols, baits, dusts and traps. Most are nerve poisons, and all must be used according to instructions. The German cockroach is already resistant to many insecticides.

Periplaneta americana cockroach mouthparts

Native British cockroaches

  • Ectobius palidus, the Tawny cockroach
  • Ectobius lapponicus, the Dusky cockroach
  • Ectobius panzeri, the Lesser cockroach

The 3 native species are found mainly in southern England. In all 3 species the male can fly, but only the Tawny female can fly; the other 2 do not have fully developed wings.