11/2/2021: Thoughts on potential Serratia infections in roaches

Among the many things I’ll be working on this fall/winter is a revised Cockroach Husbandry guide. It’s been… Quiiiite a while since I’ve updated it, and I’ve learned a lot since then.

Apparently one of the most useful parts of the guide is the cockroach illnesses/health issues section, and I’m glad such eclectic knowledge can be put to good use. One condition I had noted was “reddening”, wherein certain roach colonies can become overrun with red or orange individuals.

Initially this was thought to be some sort of genetic color variation, however upon sending a group of afflicted Archimandrita tesselata as culls to a friend, the condition of those roach completely reversed in his care. While this doesn’t rule out epigenetic mechanisms, it is very suspicious that a husbandry change could reverse the condition.

Upon exposure to more literature I now suspect infection with Serratia is the most likely explanation for these individuals. This genus of bacteria is very common in many environments (if you’ve noticed a reddish slick on wet spots in your bathroom, this is a colony of one type of Serratia) and considering the poorly documented biology of roach pathogens it’s possible this is a species that has specialized to infect roaches.

Unlike other insects infected with Serratia, roaches even with severe infections can mature and reproduce alright, albeit with some reduced fitness. I have noticed the symptoms tend to be less noticeable in infected adults, and this may have to do with where the bacteria resides: in the cuticle.

Infected individuals tend to have thinner, more malleable exoskeletons than uninfected ones. In Blaptica dubia, this has lead to a few desperate attempts to breed for an aesthetic, “thinner-skinned” strain under the assumption it will be much easier for reptiles to digest. The “Gold” line, while possessing a thinner cuticle, does not seem to be the result of Serratia infection, but does demonstrate the reduced vigor from the thinner cuticle (for those interested, I have been working the last 5 years on an improved “Gold” line that does not seem to suffer the same problems as the original, albeit with a less dramatic phenotype).

As for treatment, I have struggled for years to pinpoint the exact causes of flare-ups, but they seem to be tied to not having enough food, irregular watering, or improper temperatures. In general, stress seems to be a big factor, but the roach species and infecting Serratia strain may also play a role.

I’ll be attempting to culture extracts from various infected roaches using some techniques my excessively intelligent and far more lab-skilled girlfriend Jenn has told me, and hopefully all my suspicions are correct and some nice red bacterial cultures will pop up in vitro. The next questions from there will be if a treatment can be developed to permanently correct the condition… and whether or not this is a novel species of Serratia.

-Kyle