In 1915, Franz Kafka wrote The Metamorphosis, a novel about a man who woke up one morning transformed into a verminous creature, probably a cockroach. His family is disgusted and repelled by his new form and the rest of the novel is about his struggle to adapt to the change. Why do cockroaches evoke such strong revulsion in us, and why do they flip so many of our assumptions about animals and impermanence upside down?
Cockroaches are the most successful omnivorous species to have travelled the world feeding on human food and leftovers. Their common names are misleading: the American cockroach originated in Africa, the German cockroach from Ethiopia and the Oriental cockroach from the Crimea. Cockroaches only live in many places because there are humans there. The German cockroach cannot withstand severe cold, so it depends on warm human dwellings at the colder extremes of its range. They, like all insects, are poikilothermic (cold-blooded), meaning that their temperature varies with their surroundings, and this affects their behaviour too. In cold conditions, they slow down. As the temperature rises, they become more active, and some species can fly when it is warm enough.
As they wander from rubbish bins to other food, they can pick up and spread food-poisoning bacteria, such as salmonella. Additionally, they produce a foul odour that can linger on food. Cockroach feces and body parts in dust can also trigger allergic reactions and asthma in some people. Our revulsion at cockroaches thus has a very firm basis in food hygiene and health.
One of the reasons for the German cockroach’s success in colonizing buildings is the lack of natural predators. Rats are a cockroach predator. Is this karma in action? Kill the rats and face the cockroach population explosion! German cockroaches also show adaptive selection when faced with poisonous bait. Some of them react to sugar as if it was bitter, so they avoid the sugary poison left for them. Cockroaches that reject sugar grow and reproduce more slowly than cockroaches attracted by it, so in areas where traps are laid, the sugar-rejecting cockroaches predominate, and elsewhere the sugar-attracted cockroaches are more numerous.
But not all cockroaches are reviled. There are about 4600 species of cockroach. Some, such as the Madagascar hissing cockroach, are kept as pets. They have even been eaten, though cockroach-eating competitions like the Halloween-themed Fright Fest at American amusement parks are about shocking the audience, not nutrition. The Madagascar hissing cockroach contains a mild neurotoxin, making it difficult to swallow.
Tourists visiting the mainly Buddhist country of Thailand also report that the locals sell and eat a variety of insects, including cockroaches. However, this seems to have stemmed from lack of entomological knowledge in the tourists. The maeng daa or giant water bug, once fried, looks very similar to an American cockroach but it is not closely related. It is a predatory, carnivorous beetle that feeds on aquatic invertebrates, snails, crustaceans, fish, and amphibians, therefore it does not live in human rubbish dumps where cockroaches pick up disease-causing bacteria.
People make very different choices about what is acceptable as food. Many people choose vegetarianism for moral or religious reasons. Westerners are often revolted by the thought of eating insects, but do so anyway. Take a look at the packet of any red food; if the ingredient list includes cochineal, carmine or E120 then it contains crushed beetles. Westerners seldom intentionally consume insects other than the cochineal beetle, but that might be about to change.
Being able to make a choice of preference or morality about what to eat is a luxury. Choosing to dedicate large areas of grassland to feeding herbivores until they are big enough to slaughter for meat is a very obvious luxury. Being able to put together a balanced vegetarian diet of different plants that provide all the essential amino acids and vitamins is a different challenge. As the population of the planet continues to grow, humans might start eating more insects.
The United Nations Food and Agriculture Organization (FAO) sees animal agriculture as a major contributor to climate change, pollution, deforestation and the reduction of biodiversity so efforts are being made to develop food sources that are more efficient than cattle, sheep, pigs and poultry. Cattle convert only 10 per cent of their food into body mass, silkworms may convert as much as 31 per cent and other insects have a similar efficiency. People with a diet that heavily depends on grain may lack the amino acid lysine, which many insects provide. Insects may be a good source of protein and vitamins for those who do not want to become vegetarian, but given their tendency to carry diseases and trigger allergic reactions, cockroach farms are unlikely.
So what is the future for cockroaches? They have a very long history, fossils have been found from the Carboniferous period, 320 million years ago, so they pre-date the dinosaurs. They are tough and adaptable, being able to withstand ten times the radiation that would kill a person. If humanity ever wipes itself out with nuclear weapons, cockroaches, along with fruit flies, are likely to be the survivors. What does that say about our foibles, travails, and weaknesses?