Cockroaches

The topic of today’s blog is everyone’s favourite creepy-crawly: the cockroach. The English word “cockroach” comes from cucaracha, which is the Spanish word for the bug. They first evolved in the Carboniferous period, about 320 million years ago. Despite the millennia separating the first cockroaches from today’s, modern cockroaches still look extremely similar to their most ancient ancestors. Over 4,600 cockroach species (only thirty of these are classified as pests) have been identified across the world, although the distribution of this diversity is not uniform. There are over 450 different species of cockroaches in Australia, while only fifty have been discovered in North America. They are generalist insects; unlike many other bugs, they have not evolved adaptations to particular food sources. This allows them to tolerate a wide range of environments, from the tropics to the Arctic.

Behaviour and Appearance




Swarming German cockroaches


For those who are lucky enough to have never seen a cockroach up close, they are insects with a relatively small head, a broad flattened body, and most are reddish brown to dark brown in colour. A few species, such as the Madagascar hissing cockroach, make an audible hissing sound. A few others chirp, but most cockroaches don’t make any sound at all.

Many cockroaches are social insects. Social cockroaches live together, and parents care for their children after birth. Pheromones in their fecal material are used to communicate things such as the location of a good source of food, or of a perfect hiding place. This behaviour has exponential results as more cockroaches congregate. More pheromones will be released, leading to even more roaches joining the crowd. The only other piece of information cockroaches use to determine where they will look for food or shelter is how dark a place is, as cockroaches are nocturnal. However, once a critical mass of cockroaches gathers, more will accept it as a hiding place, even if it is bright and exposed. Isolated cockroaches will generally flee when exposed to light, so if you are seeing cockroaches during the day, there are probably quite a few of them hidden in the cracks and walls of your home.

Their preference for dark places leads them to nest in cracks and crevices. Beyond just liking the dark, they also prefer the feeling of solid objects in contact with their bodies, which is why they will cram themselves into small holes. Cockroaches also prefer to rest on wood, rather than on metal or other non-porous surfaces. This is why they can often be found living in wood cabinets or cardboard boxes. They’re attracted to sources of food and water, and they will eat almost anything. That includes plants, common pantry items, paper, leather, soap, toothpaste, cloth, and even book binding glue. Cockroaches will often enter heated structures to escape cold weather, as they originated in the tropics and prefer warmer environments.

Effects on Humans




A German cockroach in a kitchen


Many people believe that cockroach infestations are caused by uncleanliness, but they can invade even the cleanest kitchen. Cockroaches will infest everything from homes to restaurants, ships to airplanes. They can be brought into a home in boxes, grocery bags, furniture, and other items carried into the building. People occasionally bring roaches home from vacations in the US or the Caribbean. German cockroaches usually follow this strategy of hitching a ride inside. Other species simply invade from the outside through open windows or cracked wood, or even through sewers and drains. Once inside a building, they can follow water pipes and electrical lines through walls from one room to another, and from one apartment to another. Once inside they can spread without being seen, hidden either by walls or by the cover of darkness. Beyond looking gross, a cockroach infestation can have many negative effects on the inhabitants of a building. Cockroaches carry a wide range of diseases which are harmful to humans, such as E. coli, Salmonella, Dysentery, Typhoid Fever, and Poliomyelitis. These diseases can be deposited on food and food preparation surfaces, where people will be exposed to them.

Cockroaches have also been linked to an allergic reaction in humans. Small pieces of their fecal matter can be deposited on fabrics and furniture, acting similarly to dust allergens. The symptoms of the allergic reaction can include dermatitis, itching, swelling of the eyelids, and respiratory conditions. Extended exposure can even increase the risk of glaucoma. In a Chicago study, about 60% of asthma patients were also sensitive to cockroach allergens, heightening the chances of an asthma attack. These allergens can also act as an indicator of the presence of cockroaches. Approximately 20-48% of homes with no visible signs of cockroaches have detectable cockroach allergens in their dust.

Only four common cockroach species in the GTA are pests. These are the German cockroach, American cockroach, Oriental cockroach, and brown banded cockroach. The other common North American species, the wood cockroach, is not a pest. Of these, German cockroaches are the most common household pest. Each species has their own distinct quirks, but that’s for another post!

Cockroaches haven’t only been seen as pests. In some places, they’re seen as food! Cockroaches are a common snack in Mexico, Thailand, and China. Even in Northern America, cockroaches fried with garlic was a common remedy for indigestion in 19th century New Orleans.

Trivia




An aquatic cockroach in Borneo


Cockroaches are a very diverse and adaptable group of insects, which has led them to develop some very interesting characteristics! The world’s heaviest cockroach is the Australian giant burrowing cockroach, which reaches 9 cm in length and weighs over an ounce. Some cockroach species have evolved ways to survive without access to water sources. Others are aquatic, living at the water’s surface and diving to forage for food. A few species are even able to survive temperatures of -122 C by manufacturing an antifreeze made from glycerol.

The resilience of cockroaches is legendary. Some can go for forty-five minutes without air. Decapitated cockroaches keep some behavioural functionality, including shock avoidance and escape behaviour for up to half an hour before truly dying. A common myth is that cockroaches can survive nuclear explosions. While this is not true, they certainly are more resistant to the radiation which would linger in the aftermath than humans are. The reason for their higher radiation resistance is that all cells (cockroach or human) are most vulnerable to radiation when they are in the process of dividing. Human (and most other animal) cells divide almost continuously, but cockroach cells only divide when the roach is undergoing a molt. This happens about once every week, meaning the radiation has fewer chances to cause mistakes in the division process.

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