Cockroaches are ancient insects that have lived in this world for approximately 250 million years. This is an estimate from the fossils discovered. There are approximately 4,000 species of cockroaches around the world.
Medical and Sanitary Significance of Cockroaches
Cockroaches have medical and sanitary significance because they are the main carriers of various diseases such as virus, bacteria, fungi or protozoa to human beings. Such diseases may come with their legs or bodies when they go out to find food in dirty areas or such diseases may be eaten by cockroaches and are accumulated in cockroaches’ digestive systems causing contamination in the food or containers that cockroaches move past. The mechanism of disease spread results from the habit of finding and eating food in dirty areas such as in feces. Also when cockroaches move, they regurgitate and release feces throughout their paths. Hence, most diseases that are carried by cockroaches are related to the digestive system for instance, diarrhea, dysentery, typhoid and food poisoning. However, cockroaches also carry other diseases such as leprosy, plague, hepatitis, asthma, allergies or skin diseases. Moreover there has been a report that cockroaches may act as intermediate hosts of various parasites such as Ancylostoma Duodenale, Ascaris Lumbricoides, Hymenolepis Nana, Taenia Saginata and Schistosoma Haematobium.
From researches both in Thailand and abroad, it has been found that cockroaches are an important factor that causes allergies and asthma especially in children. Cockroaches will release allergens onto the areas that they walk past or into the air. When human beings are continually exposed to these allergens for a certain period of time, they may develop symptoms of these diseases. It is believed that these allergens come from feces or some substances on cockroaches. Researches from various sources state that there are a number of allergy and asthma patients who have been tested positive to the allergen test with samples extracted from American and German cockroaches. Thus, it can be clearly seen that the two types/species of cockroaches are the main factor that has led to such diseases.
Biological and Ecological Features of Cockroaches
Life cycle and Ecology
Cockroaches have incomplete metamorphosis in their life cycle. This is a life cycle that involves changes in shape and size. There are three phases of cockroach life cycle namely;
Larvas look similar to adults. In the first period, larvas that have just come out from their eggs have no wings. After 2-3 moltings, their wings and sexual organs will be developed into adults with complete wings and sexual organs. Eggs are covered with ootheca that look like beans. Most of them are red-brown in colour. The number of eggs in each ootheca differ depending on the species. Normally, there are 16-30 eggs in each ootheca. Cockroaches may lay several sets of eggs. Some species can lay 90 sets of eggs. Egg laying differs from species to species. Most like to lay eggs in closed cupboards, drawers or paper boxes. Moreover, they may lay eggs in nooks and corners of a room. Sometimes, they may lay eggs next to a wall or a furniture. Cockroach eggs will hatch within the period of 1-3 months. An adult cockroach has a flat and oval shape like an egg. Body length is from 1 to 8 centimetres. Cockroaches have a variety of colour from light brown to black. Some species may have other rare colours such as orange or green. In general, female cockroaches are larger than male cockroaches. Their heads look like rose apples which means that the top is larger and it continues to narrow down towards the bottom. The head may move independently. The head is attached to the thorax by a small neck. Cockroaches may or may not have wings. Normally, those with wings have two pairs of wings. The first pair is stronger than the second pair. The last pair is more like thin films under the first pair of wings even though the cockroach is able to fly. However, typically, they like to walk or run. Cockroaches fly only when they are disturbed. They have three pairs of legs. The front pair is smaller than the rear. Their legs are made for running thus they run really quickly. They have one pair of narrow and long antenna. There are a lot of small hairs around the antenna. A cockroach has a chewing mouth that is able to consume all types of food be it plants or animals. However, they usually take in starch or sugary leftovers, animal or insect carcasses, saliva, phlegm, feces, papers or even fabrics.
Cockroaches have a habit of eating and defecate throughout the ways they walk. They like to find food at night and to be in a group. However, there are some that find food during the day. Cockroaches have the origin in a warm climate area. Nowadays, it has been found that they have spread around the world. This may have been because they travel to different places by being in packages or wooden boxes that are transported on ships or lorries. However, cockroaches are found more in areas with hot climate than that with cold climate. Cockroaches like to live in houses, drainage pipes, shops, restaurants, kitchens in hospitals or hotels, agricultural product or paper storage buildings. They like to live in dark and warm places with high level of humidity. If one spots only a few cockroaches during the day, it will mean that the area has a lot of cockroaches. Moreover, carcasses of dead cockroaches, molts, hatched ootheca and cockroach data are also telling of the number of cockroach population.
Important Species of Cockroaches
Cockroaches that are widely found in Thailand
1. American Cockroach, Periplanta America
- The largest species of cockroach found in households.
- Shiny red-brown body.
- 2 large black dots on the head which are in yellow circles
- Antenna are slender and longer than its body
- Male length 33-40 millimetres, Female length 30-35 millimetres.
- Its wings are as long as the end of the abdomen
- Widely found along drainage pipes
- Start breeding 4-7 days after becoming adults
- Lay16-28 eggs at a time (1 ootheca)
- One female is able to lay 22-40 oothecas
- Eggs will hatch within 30-46 days
- Adults have age spans of approximately 212-294 days
- They like warm and humid weather.
2. German Cockroach, Blattella Germanica
- Small species
- Antenna are slender and longer than its body
- Male length 11 – 13 millimetres, Female length 11 – 15 millimetres
- Wings may be a little bit longer or shorter than the abdomen.
- There is a black stripe between the two eyes.
- Body is of faded brown but glitters. Its legs have lighter colour than its body.
- This type of cockroach can be found in the kitchen, shelves, drawers, desk nooks or storage boxes.
- During the day, these cockroaches will hide in places inaccessible by human beings.
- If there are many of them, they will be found in the ceiling and the spaces between walls. Moreover, they are found along the cracks of footpaths, bushes and rubbish bins.
- Their age span is approximately 100 days.
- They like warm climate.
- They breed 7-10 days after becoming adults.
- Female cockroaches with eggs will have egg shields attached to their abdomen all the time until the eggs are ready which takes about 2-4 weeks.
- They breed very quickly.
Methods to control cockroaches
1. Chemical Control One chooses appropriate hazardous chemicals according to the following principles;
Dust: Should be used in the areas where one cannot use liquid spray for instance electrical switches, electrical plugs, machines or various electrical appliances.
Bait: should be used after spraying most cockroaches or in the areas where the number of cockroaches is not so high.
Liquid Spray: should be used in areas where cockroaches like to hide as well as the food sources of cockroaches. The purpose is to kill cockroaches immediately or to have the residue effects for a long period of time.
2. Control through sanitary and environmental sanitation methods using the principle of 5S (Seiri-clear up; Seiton-organising; Seiso- cleaning; Seiketsu-standardising; and Shitsuke-training and discipline)
3. Mechanical Control using baits and traps
4. Physical Control Checking products, objects and using vacuum cleaners.
5. Using growth-control substances such as Insect Growth Regulator (IGR) which is active and provide results in the long-term.
***From the Manual for Personnel responsible for the use of hazardous materials at work, The Food and Drug Administration, Ministry of Public Health