Why cockroaches are so resilient

Cockroaches have some of the worst PR in the animal kingdom. With a better agent, their story could be that of a hardy insect that has successfully thrived on every continent except Antarctica. People would talk of the incredible diversity of the 4,600 cockroach species and their elaborate behavioral rituals and social patterns. Instead, the couple dozen roach species that interact with human habitats have stolen the headlines. Cockroaches are instead bywords for filth and grime, with much of our knowledge of these bugs being on how to exterminate them from our homes. 

What makes cockroaches so successful, and why do the vast majority of these billions of bugs remain a total mystery to science? 

The most globally dispersed cockroach species–the German cockroach–is a resilient domestic pest. “They’re just basically the perfect kind of species to take over,” says Warren Booth, an urban entomologist. These hardy bugs have a long list of pest superpowers. If a pair of cockroaches enter a new home, they can start an infestation quickly. One female German cockroach can lay around 40 egg cases at once and will lay around 200-250 during her lifetime. 

Its closely related cousin, the American cockroach, can go further. If a single female American roach wants to start a new family, she can do so without waiting for any male cockroaches to turn up. They can produce parthenogenically, meaning that fully-formed cockroach offspring can develop from an unfertilized egg. 

“These things are incredibly robust,” says Booth. Pest cockroach species can even regenerate severed limbs without much fuss. “They can do that with their internal tissues. They could lose their entire trachea, and then that can regenerate,” adds Booth. Finally, roaches can eat almost anything and can survive on waste alone.

Faced with a rapidly reproducing, regenerative insect Terminator, humans reached for chemical weapons. The discovery of the insecticide DDT in the 1940s kickstarted what Booth calls an “arms race” between ever-more-deadly chemicals and the adaptable cockroach genome.

The indiscriminate use of insecticides over subsequent decades succeeded in decimating populations of beneficial bugs like honeybees, accumulated poison inside larger wildlife with devastating health effects, thinned the shells of vulnerable bird species, and even hiked cancer risks in people exposed to the toxins as well as in their children. Despite the senseless scale of this collateral damage, the crushing chemical broadside made not even the slightest dent in the side of the Team Roach. Within a few years, cockroaches resistant to DDT started emerging. Modern-day cockroach populations resist virtually every insecticide cooked up between the 1940s and the 1990s. Booth explains that these cockroaches can produce detoxification enzymes that rapidly break down damaging chemicals. 

Part of the problem is the vast scale of cockroach communities. Booth explains that while some bee species rely on a single queen to reproduce, cockroaches can count on thousands of their kin reproducing at scale. This provides much more scope for helpful resistance gene mutations to emerge. 

Pest cockroach species have fully earned their reputation as unkillable insect juggernauts. But this scary surface masks a diverse world of much more delicate insects that play vital roles in our biosphere. Darby Proctor, a behavioral researcher at the Florida Institute of Technology, runs Roach Lab, an educational platform that teaches undergraduates how to conduct behavioral experiments using the discoid cockroach as a model species. 

Discoids aren’t a pest species and show surprising behavioral complexity. They can be trained to do simple tasks. Human psychology studies show that people complete tasks differently when onlookers watch them. In Proctor’s latest roach work, her students are testing whether pairs of cockroaches can complete maze tasks faster than when alone. She’s also investigating whether cockroaches have preferred social partners. “If this were a primate, we would call that ‘friends’,” she adds. 

These complex social dynamics are matched by the vast number of important roles cockroach species play. Roaches are a vital feed source for agri- and aquaculture, and are used for waste management in some Asian countries and even as cosmetic ingredients. Many species live in the rainforest, where they make up an incredible 25 percent of the biomass in the forest canopy. “If we didn’t have cockroaches,” says Booth, “rainforests fall apart because they’re the primary decomposers.” These non-pest species are also much more delicate animals that would die in a domestic setting, says Booth. 

Many rarer and more useful species live far from the human eye, whereas German cockroaches live only inside human dwellings. The common view, says Booth, is that “a cockroach is always a cockroach pest.” A deeper look at this incredible grouping of animals shows that this view, at best, fails to pay respect to pest animals that have survived through incredible resilience and, at worst, ignores essential contributions to our most precious environments. In her Roach lab, Proctor has at least gotten her small group of would-be entomologists to appreciate the value of these tiny bugs. “If one of their cockroaches die, they’re real sad about it,” she says. 

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