In your yard: cockroaches

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An old quote of unknown origin that dates back to the mid-1990s goes: “After a nuclear war, the only living things left will be cockroaches and Cher.” Well, we can’t say what the famous singer’s fate will be, but that may not be much of a stretch regarding cockroaches—they can withstand doses of radiation that would be lethal to humans. And, fossil evidence shows they’ve already been around for 320 million years, since the Carboniferous Period.

There’s more: Cockroaches can hold their breath for up to 45 minutes, deliberately slow  their heart rate, go without food for a month, and live without their head for a week. They run at close to three miles-per-hour (5 km/h) and have such fast reflexes they can turn completely around in 1/25th (0.04) of a second.

And, get this: Scientists discovered that some species have surprisingly human traits: They’re very social. They recognize members of their own family, and many generations live together. They have egalitarian social structures based on rules and can make group decisions. Also, like some humans, their health fails if they have to live alone.

Beneficial? Indeed!

Okay, so it’s established that cockroaches are survivors, and probably smarter than a grub, but what does that matter, what good are they? Well, like all other creatures on earth, they’re important in their own way: They’re a food source for birds, frogs, lizards, snakes, and mammals (including humans in some locales). And, they’re essential recyclers of decomposing plants and animals—what goes in their mouths comes out as enrichment for the soil. Those that invade human structures are pests, to be sure, but others—which includes all but four species—are beneficial.

Still, cockroaches are viewed as filthy, especially if they find their way into a kitchen. To be sure, no one wants them there, but lovers of cockroaches (yes, they do exist!) beg to differ regarding their hygiene. They claim that cockroaches’ bad rap is unfair, that, in reality, they routinely groom themselves to stay clean. The problem, it seems, is they aren’t picky about their food and will nibble on everything they come across, from tiny bits of spoiled meat to moldy crumbs. Consequently, when contaminated food goes in, contaminated feces come out. Some experts insist that only an unsanitary kitchen produces an unsanitary cockroach.

Cartoon of a cockroach mugshot in jail.

9© gan chaonan / Shutterstock)



Their appearance in a house often has nothing to do with its cleanliness; they’ve just inadvertently hitched a ride in boxes, firewood, furniture, and sometimes grocery bags. Or, they wandered in through loose-fitting doors and windows during weather extremes.

Once in, loathe to leave

Once they’re in, they find myriad reasons to stay: Furniture or appliances to hide under, or even sliver-sized spaces in baseboards, cabinets, and floors are enough to provide safety. Humidity, which most species like, is to be found in or under sinks. Food is readily available—a tiny breadcrumb on the floor can be an entire meal for a cockroach.

Some background

Cockroaches belong to the order Blattodea (blah-TOAD-ee-uh), along with termites. “Cockroach” is taken from the Spanish word, Cucaracha (koo-kuh-RAH-chuh), meaning chafer beetle.

Cockroaches are found everywhere in the world, except the Polar Regions, although they’re mainly tropical. There are around 4,000 species, and only four make pests of themselves. Nocturnal insects, they spend the daylight hours hiding in cracks and crevices or under yard debris. When they appear at night, we usually get just a glimpse as they scurry away with the flip of a light switch. They don’t need a light to alert them, though—research in Finland has shown they can see in near-total darkness.

About 57 species, ranging in size from about 0.5 to 2.0 inches (1.2–5.1 cm), inhabit North America. The most common are the German (Blattella germanica), American (Periplaneta americana), Brown-banded (Supella longipalpa), and Oriental (Blatta orientalis).

Physical characteristics

Cockroaches have three body sections: head, thorax, and abdomen. They have a flattened, long-oval body that looks pretty much like the oldest discovered cockroach fossils. The body is covered by a hard skeleton (exoskeleton), and they’re reddish-brown, sometimes black. They have three pairs of legs with claws, and usually two pairs of wings.

The head

The head, small, oval, flattened, and downward bent is often hidden from view when the insect is observed from above, which is how most of us see them. A flexible neck allows the head to move in all directions. The cockroach has a brain with 1,000,000 tightly packed brain cells, two large, apostrophe-shaped, compound eyes, chewing mouthparts, and two antennae. A plate behind the head, called the pronotum, has markings that help to distinguish species from one another.

German Cockroach standing on white surface.

German Cockroach, Blattella germanica, the most common in the United States. (© Protasov AN / Shutterstock)



The compound eyes are composed of 2,000 individual lenses, called ommatidium, each of which sees its own tiny portion of an entire picture, which the brain then interprets. The antennae are long, thready-looking, used for detection of food, and as feelers —when a cockroach walks alongside a wall, for instance, it will keep an antenna in contact with it.

American Cockroach on white background.

American Cockroach, Periplaneta americana, the largest species in the US. (Insects Unlocked Project, Univ. of Texas / Flickr; PD)



Thorax

The thorax is the middle section. Attached are the legs and wings (for cockroaches that have them). The legs have spines and are strong, the back ones especially so—they can propel cockroaches up to 50 body lengths per second. Sharp claws on their feet can cling to the tiniest imperfection in a surface and enable them to scale walls and cross ceilings.

Not all cockroaches fly. Those that do so fly fairly well, though only for short distances. Most use their wings for gliding. Usually, males have wings, but most don’t use them or use them only for gliding. Females often lack wings or have only vestigial ones, which are small and undeveloped.

Abdomen

The abdomen is the largest part of the cockroach’s body, and it holds internal organs associated with circulation, digestion, respiration, reproduction, and elimination of body waste.

The heart is long and tube-shaped. Unlike that of a human, the blood is clear because it doesn’t contain iron to give it a red color. Called hemolymph, it doesn’t carry oxygen; its job is to transport nutrients throughout the body.

Cockroaches breathe in and out through ten pairs of slit-like openings, controlled by valves, located along both sides of their body—eight pairs along the abdomen and two pairs in the thorax. They’re called spiracles, and each attaches to a trachea that networks through the body.

They have a simple digestive system that’s modified with a crop and proventriculus to hold and pulverize the tough cellulose and other materials cockroaches include in their diet. Two conspicuous appendages at the end of the abdomen, called cerci, function as sensory organs for detecting air movement; they alert the cockroach to approaching danger.

Life cycle

Cockroaches go through incomplete metamorphosis, called hemimetabolism. They progress from eggs to nymphs (developing young) to fully grown adults.

The breeding season runs from March to September. A female mates only once and will hold enough sperm to produce 15 to 40 ootheca in her lifetime. There are a few exceptions, but here’s what generally follows mating:

An egg case called an ootheca (oath-EE-kuh) forms around fertilized eggs within the female’s body. The ootheca holds 12 to 25 eggs and is made up of proteins that become hardened to protect the contents. This takes about a day. The female carries the ootheca around for several days, with it sticking out at the end of her body. After that, she drops it in a dark crevice or buries it in debris or soil. Some species, like the American Cockroach, carry an ootheca until the eggs are just about ready to hatch.1

Here’s a curious fact: Some small colonies of American Cockroaches are parthenogenetic: They’re females who give birth only to females that give birth only to females, and so on. No males exist.

Brown cockroach egg sac, or ootheca, laying on sandy surface.

Cockroach egg case (ootheca). (Jean and Fred / Flickr; cc by 2.0)



Nymphs

The eggs hatch in six to eight weeks. The young, called nymphs, look like tiny, wingless versions of their parents. They’re paler at first, but darken as they develop. They’ll shed (molt) their exoskeleton, which is not expandable, from 10 to 13 times as they grow, depending on the species. At the time of their final molt, they’re fully developed. It can take up to a year or more, depending on the species, to reach adulthood. A full lifespan is up to three years.

Differences between male and female

Here are some of the more obvious differences between a male and a female.

  • Male’s body is usually smaller and has a slender abdomen
  • Male’s wings extend beyond the end of his body
  • The end of the male’s abdomen is pointed, and a female’s is blunt
Male and female Dubia Roaches on a white background.

Dubia Roaches, blaptica dubia. Male at left, female at right. (© Holger Kirk / Shutterstock)



Habitat

Most cockroaches like it dark, damp, and warm. They’re nocturnal animals and hide in groups during the day under mulch, bark, rotting logs, stones, or in storm drains, basements, and buildings. They especially like kitchens, grocery stores, bakeries, and the like.

Food sources

Cockroaches are omnivorous scavengers. They eat nearly anything, including all kinds of human food, pet food, garbage, grease, paper, wood, leather, and even wallpaper paste.

1 Some cockroaches give birth to live young, the Madagascar Hissing Cockroach, for example.

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