Look out! It’s a cockroach
Geetha Iyer
“The study of roaches may lack the aesthetic values of bird-watching and the glamour of space flight, but nonetheless it would seem to be one of the more worthwhile of human activities.” – H.E. Evans – Life on a Little Known Planet
Looking out for cockroaches is one activity humans indulge in to ensure that they do not invade our living space. Despite the best of our efforts, cockroaches have the upper hand and effortlessly enter spaces occupied by humans. Which then raises a question: have we really studied the cockroach or just ‘watched’ it long enough to squash or spray it? The escape response of the cockroach has been clocked at 40 milliseconds (a millisecond is one-thousandth of a second), no wonder they get away from many of us easily!
Cockroaches are studied in our biology classes. They are the chosen examples in the middle to high schools for studying insects or when permitted, for performing dissection. The latter mentioned activity is no longer a part of school curriculum, but most of today’s biology teachers would remember dissecting cockroaches to study their systems. Has all this made us any the wiser about the cockroach?
There are about 5000 species of cockroaches found worldwide, of which only 1 per cent are pests. The rest live away from human habitations and are ecologically important creatures of their habitats. As we are familiar only with the pest species we think of them only with disgust. How different are they?
Cryptocercus sp is a cockroach found in montane forests that is capable of fixing atmospheric nitrogen. Many cockroaches found in tropical areas harbour methanogenic bacteria in their hindgut and hence emit methane. Would they be contributing to climate change then? A question to ponder in the biology class. A study in 1997 found that in the lowland forests of Borneo, cockroaches were the main pollinators of the plant species found in the understorey. It is believed that in tropical forests there might be a variety of ecological relationship between plants and cockroaches. Epilampra irmleri found in the forests of Central Amazon is responsible for the consumption of 6 per cent of the annual leaf litter. L N Anisyutkin, a Russian entomologist believes that from an evolutionary point, the cockroach species of South India and Sri Lanka may represent possible links between the fauna of Gondwana and Laurasia.
For the classroom
1. For very long we have thought of cockroaches as an aid in teaching science and as a dissection specimen. This poem may be a worthy one for introducing values – the idea of reverence for all life forms, as well as have some fun in the English class.
Is there nothing to be said about a cockroach which is nice?
It must have done a favor for somebody once or twice.
No one will speak up for it in friendly conversations.
Everyone cold-shoulders it except for its relations.
Whenever it is mentioned, people’s faces turn to ice.
Is there nothing to be said about the cockroach which is nice?
– M.A. Hoberman, “Cockroach”
This is just one of the three stanzas from the delightful poem that has been set to music. The notation for the music and the rest of the stanzas may be accessed at https://www.jwpepper. com/10090098.item#/submit)
2. Lesson in hygiene and sanitation:
Rarely do schools think of using cockroaches to study hygiene and sanitation.
Cockroaches basically look for decomposing materials; they are garbage collectors which is why they are found in sewers and other such places. Their presence is the first sign that the hygiene has been compromised. What can be done?
Use the following questions to initiate a discussion on hygiene and sanitation and also help students put in place some healthy practices to be followed in their school and home.
i) Use of pesticides should be the last option. Why and when? (Hint: Indoor pollution; infestation)
ii) Kitchen and bathroom hygiene are equally important but rarely given attention in most homes. What aspects in the kitchen need to be looked into? (garbage bins; hand towels; leftover food; badly closed utensils.)
What can be done? (vessels stacking in sinks, garbage storage; cleaning trashcans, towels and scrubbers washed, dried and stored outside the kitchen.)
Bathrooms: How is bathroom hygiene compromised? (Hints: Keep bathrooms dry; clean basins, floors and drains regularly; seal openings in drains; a dustbin with cover to keep bathroom trash; diligent use of flush)
Air clothes before storing them in laundry baskets. Why? (This will get rid of sweat and odour both of which attract these pests. Keep drains closed and clean.)
iii) Cockroach predators: Who are they and can their presence be encouraged?
iv) Importance of hygiene and sanitation in maintaining our health.
3. Investigation: Scientists all over the world are studying cockroaches to learn their escape mechanisms in the dark. How do they behave when there is an obstacle in their way and how do they then navigate. Based on their studies, robotic cockroaches are being made that can help soldiers navigate in areas where landmines have been scattered. Students can study this for a project for a science fair.
Keep a cockroach inside a glass aquarium. Cover all sides with black paper leaving a small portion for your observation. Keep several objects scattered inside that will act as obstacles. Observe. Collect and analyze data. Using a small motor/battery, assemble a small toy that will demonstrate how cockroaches avoid obstacles. Hint: Observe their antennae specially. You may want to improve your experiment based on your observations. An Internet search will provide you with research papers on this topic.
Pest species
The most familiar cockroach pests are Periplaneta australasiae (not Pamericana as is generally taught in all biology classes) or the Australian cockroach and Blatella germanica or the German cockroach. Both these are found not only in kitchen sinks but also in cupboards and storage shelves.
Two other species also move among human habitations. These are Neostylopyga rhombifolia and Supella longipalpa. While all four invade our kitchens, drains and dark corners, the last mentioned is the one commonly attacking our clothes, especially those that have been stored for washing in laundry baskets. The cockroach body is dorso-ventrally flattened making it easy for it to squeeze through the tiniest of spaces. Supella being smaller finds ways to enter the food items, if there is even a tiny gap in the lids of storage containers.
Non-pest species of cockroaches: There is a bewildering variety of cockroaches that come in colours of green, orange, pink, etc. A few found in India are briefly highlighted.
Therea petiveriana
Like other insects some cockroaches are masters of disguise. Known variously as seven-spotted, desert or Indian domino cockroach, Thereapetiveriana is found in South India. It is a mimic of the ground beetle Anthia sexguttata that sprays chemical irritants to escape from its prey. They are found in ground litters of scrub areas and help in the recycling of organic matter along with several other cockroach species in this habitat.
Epilamprine1 cockroaches:
Found all over India these exhibit remarkable parental care. The adult female carries its nymphs till they complete their second moult, on her abdomen under her wings which are held over them like a hood. The developing young get a kind of liquid food from specialized pores on the upper surface of their mother’s abdomen. The nymphs have sharp mandibles to pierce her cuticle and feed on her blood (haemolymph).
Pill cockroaches1,2
Like the Epilamprine cockroach these too belong to the family Blaberidae; are found all over India and also exhibit parental care. Perisphaerus sp. adults are black in colour. In my garden I find them in shallow hollows of the neem tree. The nymphs hatching out are white, blind and have tube-like mouthparts, which are unique amongst cockroaches. The mother has four apertures at the bases of her mid – and hind legs. The mouthparts of the nymphs fit into these pores. The nymphs clinging beneath the mother’s body for the first two instars suckle the nutrient secreted by the mother from these pores. In the third instar they develop normal eyes and body pigmentation and the nymphs are then attractively pink in colour. They grow to become the black coloured cockroaches capable of rolling into a ball like the pill millipede.
Other interesting cockroaches from across the world1:
Prosoplecta sp. from Philippines is very easily mistaken to be a ladybird beetle which it mimics to perfection. Polyzosteria mitchelli from Australia is a brightly coloured cockroach, which when disturbed will spray a pungent fluid from its abdominal glands as a warning.
References
1. http://cockroach.speciesfi le.org/HomePage/Cockroach/ Diversity/Diversity.aspx – For images of some of the described non-pest cockroaches. Informative site for cockroach diversity
2. https://www.fl ickr.com/ photos/nickadel/sets/72157631523060846/ – Pink nymph of Perisphaerus sp
Pest cockroach predators
There are many natural predators. Wasps of different kinds prey upon cockroach egg cases thereby reducing their population. Lizards are very good at keeping both cockroaches and mosquitoes at bay. Most people are wary of lizards and believe they will poison our food. If food items are kept closed then there is no chance of a lizard coming near them or falling into them. Lizards, like cockroaches, come out after dark to hunt for their food. There are also specialist spiders that feed on cockroaches. Like lizards these too need not be feared. They come out at night and do their job quietly, and will do no harm to you or your food. From personal experience I can assure you that between lizards, spiders and wasps I have been able to keep the cockroaches away successfully. If they still invade my spaces, then I know that my hygiene guard has been let down.
Fun facts about cockroach
The cockroach’s ears, located in each knee-joint, are so sensitive that they can distinguish earthquakes as small as 0.07 on the Richter scale.
Cave dwelling cockroaches are the main food for carnivorous fishes and their faeces for cave dwelling bats of South Africa.
Their population density under the canopy of shrubs in the coastal deserts of Egypt is 116000 cockroaches/Ha. According to El-Ayouty and team they are not only among the main detritivores in arid deserts around the world but also improve the nitrogen content of the soil. Their faecal pellets provide 10 times more nitrogen than what the leaf litter can provide to the soil.
A crash avoidance system for automobiles is developed based on a distributed network of artificial neurons that mimic the neural organization of the escape system in the American cockroach
The author is a consultant for science and environment education. She can be reached at scopsowl@gmail.com.
