Taiwan’s Cockroaches May Retreat as Summer Fades. But They’ll Be Back.

A few weeks ago, I decided that Taipei was in the midst of a particularly bad summer for cockroaches.

In the process of attempting to confirm this theory—based entirely on anecdotal evidence—a good friend told me that his air conditioning unit had been blowing air erratically. Being a practical fellow, he decided to investigate by pulling in the old-style unit and unscrewing the back panel to see what was going on—only to be confronted by a decaying colony of dead roaches. He estimated that a couple hundred corpses had been clogging up the fans.

His story is not as unusual as you might hope. Wang Kuo-chung (翁國忠), who runs an air conditioning installation and service company in Taipei, says it is a problem the company come across reasonably often, especially in units that are used infrequently.

“The environment in the AC unit is perfect for cockroaches,” he says. “There’s a nice undisturbed space, it’s warm and moist. Everything a cockroach wants!”

There are 75 species of cockroaches in Taiwan, but most of them are busy doing their thing up in the mountains, according to Prof. Matan Shelomi, an entomologist at National Taiwan University. Only five or so species bother to hang out in the cities.

“Some are strikingly beautiful: blue, green, black, spotted, striped,” Shelomi says. These rural roaches serve an important function of taking care of decomposing materials in nature, whereas their urban cousins have thrived thanks to the human habit of producing trash, with a particular fondness for cardboard and glue. “The city roaches happen to be the boring brown ones,” says Shelomi.

Prof. Matan Shelomi. (Photo: Supplied)

In Taiwan, the main urban roaches are the American roach and the Australian roach, both of whom enjoy sewers and street crawling—and know how to fly. Indoor infestations of German or Asian roaches are more common, while the non-flying Oriental cockroach is happy in either environment. (These names are fairly misleading in that they have little to do with the origin or habitat of the various species.)

Taipei’s hot and humid summers make for a near-perfect environment for roach populations to explode. When temperatures climb up to 30 degrees Celsius, German roaches start laying eggs at a rate of every six days, with hatching taking place around three weeks later. American roaches lay eggs every three days which hatch about 30 days later. (If you spot an egg capsule, remove it and flush it quickly!) These rates drop along with the temperature, as each five-degree drop doubles the length of the reproductive cycle.

In Taipei, with its average temperature of just over 29 degrees Celsius in June and July, it’s easy to see why roaches are so common in the summer months. The warm weather also means increased activity for these cold-blooded insects—which means you see a whole lot more of them.

A particularly wet spring can also push up roach numbers—and Taipei saw more rainfall from March to May of 2019 than it did in the springs of 2017 and 2018 combined, which may explain why Taipei’s summer of roaches appears so much worse this year. 

Some of Taiwan’s resident cockroaches are strikingly beautiful, such as the Paranauphoeta formosana pictured here.

Like many people, I have a fear of roaches which produces an immediate reaction of ‘Exterminate!’ It’s fair to say that no one wants an infestation of roaches in their home, and the pests do have a reputation as carriers of disease and as allergy triggers. But do roaches really deserve the bad rap they get?

Perhaps not, says Shelomi. “The fear can be irrational, especially [among] people who freak out seeing them in the city,” he says. Like houseflies, roaches can carry a cocktail of diseases including typhoid fever, dysentery and even polio—but they’ll only endanger you “if they walk on something dirty and then walk on your food,” Shelomi says. Even then, your chances are pretty low: Roaches, he adds, are clean creatures, spending around 50% of their day grooming and preening.

“It’s bad to have roaches in the kitchen,” Shelomi says, “but the ones in the street cannot hurt you unless you lick them.”

In general, I’m reasonably good with creepy crawlies. With roaches, however, I have identified one trigger as the otherworldly way they waggle their antennae. Perhaps, I thought, I could get past this if I understood it?

“The antennae are how they smell and also how they sense obstacles in front of them,” Shelomi says. “Humans are terrible at smelling things compared to insects. For roaches and most other insects, smell is the most important sense, not sight. They wag their antennae the same way we would move our eyes or turn our heads to see something better. It’s how they sense the world.”

Another problem with roaches is that they are fast. They run at a tidy 1.7 miles per hour and are good at evading capture because the spindles on their legs help them navigate all kinds of terrain with ease. They can even invert quickly to crawl on the underside of a surface.

While this can be a pain when you’re chasing one at home, researchers at Johns Hopkins University have been studying roaches to improve robotics. Their ability to squeeze through narrow spaces and navigate complex routes is also behind ongoing research into how an intrusion of roaches could be used to explore an area after a natural disaster and help to locate survivors.

Back in your apartment, however, Shelomi explains that they have yet another secret weapon in the form of the cerci—the two small spines that protrude from their rear ends—that act like antennae to detect vibrations in the air. “That’s why sneaking up on a roach is so difficult: they can feel the wind you produced when entering the room,” he explains. “They also can feel vibrations in the ground and can thus sense your footsteps. They otherwise have terrible hearing, however: Screaming at a roach won’t do anything to it.”

It took me two full years to accept that, in Taiwan, there are roaches that can fly. Nowadays, I have a lovely rooftop apartment with one drawback I’ve noticed in the past few weeks. Occasionally, I’ll be relaxing on the sofa outside and I’ll suddenly hear a strange whirring sound and look up from my book to see a roach gleefully launching itself over the wall and heading right for me.

I wondered: Logically speaking, since roaches are cold blooded, could the summer heat be a reason for this? Shelomi concurs that warm weather encourages flying—and reports from New York and Israel, where scientists noticed that a heatwave was encouraging roaches to take to the air and start to inhabit apartments on the fourth and fifth floors, confirm this.

“Warm weather should mean they have more energy to fly, as they probably couldn’t do that in the cold,” says Shelomi. “They might not be flying all the way up to the fifth floor, though: They can walk up between the walls and along pipes and such.”

In case you are wondering about the outlook for cockroaches in the face of global warming, research carried out at the University of Queensland suggests that roaches have evolved nicely to adapt to climate change. This adaptability is unsurprising as scientists have used DNA sequencing to date the earliest cockroaches to around 350 million years ago—putting them, among other insects, as the first animals on the planet to evolve flying skills. For roaches, a trip up to my rooftop balcony is a cinch.

Not afraid of heights: Cockroaches hone their climbing skills when the weather gets warmer.

Although I’m not fond of their flying antics, perhaps there is something totally awesome about house roaches that I am missing? Shelomi certainly thinks so. He points to a study in 2015 that found American cockroaches have personalities. “Some are bold explorers and others are shy and hide often. They are gregarious and like to live with other roaches, and they do change behaviors when in groups—they follow the group personality and are less independent.”

Shelomi shared another cool roach fact: Their limited vision range renders them blind to red light. “If you want to film cockroaches at night,” he advises, “you can use a red light.”

While the idea of filming roaches may appeal to some, I suspect that most people are not fond of having roach guests and would be rather more interested in good ways to encourage them to leave en masse. Shelomi advises against using appliances or furniture that may have come from a roach-infested house and urges that you control any leaks—roaches are attracted to moist areas, such as dripping pipes. 

“Of course, your clean apartment won’t help if your neighbor’s apartment is filthy,” he adds. “A few explorers might still wander in now and then.”

Shelomi says boric acid and silica work well as roach killers—never mind that some German cockroaches are reportedly developing resistance to pesticides. “Roaches won’t ever resist boric acid or silica since those work by physically damaging them rather than chemically poisoning them, nor will they resist glue traps or vacuuming them up,” he says.

Boric acid is particularly effective as roaches walk through the acid and then eat it while grooming their legs, then the acid damages the gut leading to death. However, it’s not recommended for households with pets or young children. Similarly effective, silica dust and diatomaceous earth dehydrate the exoskeleton, causing it to crack.

Shelomi is also keen to point out that electronic insect repellents are pointless. “Nobody has discovered any frequency of sound that insects dislike,” he says. “No electronic or sonic pest repellent works on any insect, from [roaches] to mosquitoes. All are scams.”

I’ll admit that the idea of roaches having gregarious personalities is making me a little more sympathetic toward them and I begin to wonder if death by dehydration might be a bit cruel. “Worse than squishing them?” asks Shelomi, “It’s really subjective, what form of execution makes you feel more comfortable.”

“Personally, I don’t kill roaches at all,” he says. “I’m not an animal rights activist; I just feel roaches are big enough and, yes, cute enough that I couldn’t bring myself to squish them any more than I could squish a mouse. I’ll pick them up and toss them… or try to show a more entomophobic friend that they aren’t so scary, especially if you look at their underside and can see their little roach faces.”

Cute as a button, aren’t they?

Globally, targeted roach and ant bait have largely usurped the widespread use of foggers, or “bug bombs,” to stamp out infestations. According to Shelomi, this trend may be responsible for the recent international resurgence of another dastardly pest: Bedbugs.

Reports have suggested that services such as Airbnb are partly responsible for the spread of bedbugs, as individual homeowners may not have plans in place to prevent outbreaks. Shelomi notes that visual checks for black spots along the seams of mattresses and the bugs themselves are a wise precaution to take while traveling.

Which leaves me with a hypothetical question to ponder: Which is worse? Bedbugs, or a huge roach crawling over you in the middle of the night?

Cover photo by Michael Garber and Nick Aspinwall. All other photos via Wikicommons, CC BY 2.0 unless otherwise noted