A Loving Touch Triggers Cockroaches to Make Babies Faster

Female cockroaches make eggs more quickly if they cuddle with other roaches, but artificial antennae delivering gentle touches can also speed egg growth

"Make eggs, make eggs!" Photo: Adrienn Uzsak

We humans are social creatures. But we don’t just crave physical interaction to fill the world with people: A loving touch is important for helping infants properly develop and ensuring healthy romantic relationships, among other benefits. To quote Daft Punk and Paul Williams, “Touch, sweet touch / You’ve given me too much to feel / Sweet touch / You’ve almost convinced me I’m real.”

Animals also value touch. Primates groom one another to reinforce social bonds, while elephants gently caress upset friends to calm them. But it’s not only the most sentient members of the animal kingdom that are influenced by touch—so too are cockroaches.

According to new research published in Proceedings of the Royal Society B, touch plays a very important role in roach society: it hastens a female roach’s reproductive capabilities.

Cockroaches, of course, are a major pest species, so researchers already knew quite a bit about their reproduction. Females that have higher levels of juvenile hormones develop their eggs up to several days faster than those with lower hormonal levels. Females that live in large groups, likewise, produce eggs faster.

Connecting these dots, some studies have found that antenna touches from other roaches trigger hormonal production in females, speeding the cycle of egg production. But the mechanisms within touch that causes hormones to surge—whether something specific to living cockroaches themselves, or something about the physical feeling itself—remained unknown.

The authors of the new study, entomologists and engineers from North Carolina State University who are not prone to squeamishness, wondered what it would take to mimic the baby-making roach touch. Could artificial tactile stimulation also influence egg development?

The team set up a series of holding pens for German cockroaches (the ones that tend to infest houses). They selected females that had just molted into adulthood, and anesthetized them to remove some of their oocytes, or developing egg cells. No males were involved, as cockroach eggs begin to grow in the female prior to any acts of insect intimacy.

After collecting oocyte average sizes for all of the roaches, they put single females into each of the pens, and then exposed them to a number of different scenarios, including putting in another female, putting in a dead roach or leaving the females in isolation. In other cases, they permitted another roach to only peep its antenna into the cage rather than its entire body, or allowed a roach with severed antenna to stick its head in.

To see whether or not roach-free touches can stimulate reproduction, some of the females were also exposed to artificial antennas. These included downy duck feathers or feathers stripped of all down, the latter of which most closely resembled giant roach antenna. The feathers, which were connected to a motor, could rotate around the roach’s pen, allowing the researchers to tinker with the frequency of touch. After six days, the females’ oocytes were measured again, to see how much they’d grown since the beginning of the experiment. 

The researchers built a creative roach rig to contain their creepy-crawly subjects. The inset shows a roach experiencing a duck feather massage. Photo: Adrienn Uzsak

Across the board, the team found, females that were completely left to their own devices or that were exposed only to a dead roach developed their eggs significantly slower than those that were lucky enough to land in more social cages. The roaches that were allowed to interact with other female roaches or even with female roach antenna alone significantly sped up their reproduction, but the females that socialized with the roaches with the cut-off-antenna did not. This indicates that something about the touch—not the presence of another roach—triggers the hormones.

Finally, confirming their hypothesis, the feathers served as effective stand-ins for roach antennae, especially the ones that were less downy and more barbed. Slowly rotating the feathers for occasional touches produced better results than a tactile overload at 30 revolutions per minute, the team found.

While the researchers discovered that the roaches with the fastest reproduction rates were those that were allowed to cuddle with other living cockroaches, the results indicate that touch itself seems to be at the crux of hastening production at those six-legged egg factories.

This doesn’t mean that touch is the sole stimulating factor for faster egg development—after all, the roaches that interacted with healthy, living insects friends enjoyed the fastest reproduction times. The study leaves unanswered questions such as what it is about touch that triggers hormonal surges that result in faster baby making within the female’s body.

Of course, there are more implications to the study’s results than simply teasing out some quirky details about roach behavior and physiology. The faster a female churns out mature eggs, the faster a male can fertilize those eggs and usher in the next generation of pests—and then rinse and repeat. Ultimately, the more we know about how cockroaches reproduce, the better chances we have for developing ways of quickly stopping explosive infestations that currently plague kitchens, bathrooms and restaurants across the world. 

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