© Alexey Protasov | AdobeStock

Cockroaches found in and around residences are often filthy creatures. Dozens of medically important pathogens have been isolated from cockroach pest species. In addition, allergens produced by cockroaches are both a risk factor for developing asthma and a trigger for asthma attacks, making them a significant pest of public health. But what about biting? In my 25+ years working in professional pest management, I have on several occasions encountered people who claimed to have been bitten by cockroaches. Historically, I approached these accounts with some skepticism and caution, since cockroach bites aren’t something that’s widely reported in the United States. However, upon reading a personal account by UC Riverside entomology professor Chow-Yang Lee, who described being bitten on the fingers while sleeping, the topic became much more intriguing to me.1 Domestic and peridomestic cockroaches are generalized feeders, or scavengers. They have biting, chewing-type mouthparts that are used to cut, tear and manipulate food. Their mandibles are quite powerful. A study looking at the American cockroach, Periplaneta americana, found that they can bite with a force 50 times greater than their body weight.2

Some species, including American cockroaches and German cockroaches, Blattella germanica, are known to be pests of forensic importance, feeding on dead skin and carrion. In homes with infestations, bodies of infants whose deaths were attributed to accidental asphyxiation or sudden infant death syndrome have been reported to have been discovered “covered with cockroaches.”3 This can cause interference with death scene investigations.

In fact, several cases have been reported involving cockroaches altering bodies postmortem and raising questions regarding the cause of death. In one instance, an individual was arrested for suspicion of poisoning based on patches around the deceased’s mouth.4 He was later released when investigators found no evidence of poison and further concluded that the patches were most likely caused by cockroaches.

A REVIEW

There are also a number of reports of cockroaches biting living individuals. Several authors have described occurrences of cockroaches feeding on fingernails, toenails, callouses and corns of sailors on ships. One naval medical inspector noted, “all of us” have experienced trouble with cockroaches, affirming that, “the toenails of the personnel of the Navy have long suffered from their ravages.”5

Others have shared reports of cockroach bites, particularly among those living in undeveloped regions, where high cockroach populations can occur in sleeping areas. The English naturalist Arthur Nicols described how he once found himself sleeping in a room “swarming with cockroaches (the small species).”6 He was awakened by them gnawing at his feet. Nicols observed that the cockroaches had entirely eaten away the skin of a large blister on his foot, as well as the hardened skin on his heel “down to the pink flesh.”

Many modern entomology texts cite a 1957 source by Ross and Willis when addressing the question of cockroaches biting humans. After examining a number of references and reports, Ross and Willis concluded, “Admittedly, many of the accounts lack the authenticity of direct personal observation, but even so, this body of evidence cannot be ignored…cockroaches may incidentally bite man.”7 Kramer and Brenner add, “there are other accounts of bites around the mouths of infants in heavily infested homes, and even in hospitals.”8 Others have offered similar remarks about cockroach bites.

But overall, little new information on the topic has been published since 1957, with the exception of a significant publication in The International Society of Dermatology in 2013. In their report, zoologist Wilson Uieda and dermatologist Vidal Haddad Jr., M.D., describe the presence of German cockroaches feeding on the skin of villagers in the Brazilian Amazon. They share images of the skin of children with “acute lesions covered with crusts and small whitish scars caused by cockroach bites that occurred when the subjects were sleeping.”9 Their observations provide contemporary evidentiary support to the many older reports.

BITE OCCURENCE

On a large scale in more developed countries like the United States, cockroach bites are very rare. However, individuals living in a residence with a severe cockroach infestation are much more likely to have a cockroach gnaw on them than the average person. Uieda and Haddad note that bites may occur “especially in children who live in areas of urban poverty.”

Indeed, urban entomologists working in these environments have commonly encountered cases of cockroaches biting people. Entomologist Joe Barile notes, “multiple times in my career working in low-income housing, I’ve seen wounds from cockroaches on children and elderly, typically from cockroaches feeding on food residues on their skin. I’ve also seen children who’ve experienced eyelash loss from cockroaches gnawing around the eye, perhaps induced by the oily substance produced by sebaceous glands” (personal communication March 15, 2021).

To be clear, the bite of a cockroach is not like the “bites” we’re familiar with from the vast majority of other insects. Most insects that are known to bite humans are blood feeders, including mosquitoes, fleas, kissing bugs, sucking lice and bed bugs. These insects don’t really “bite,” but rather they have piercing- sucking type mouthparts designed to penetrate the skin and siphon out blood.

Cockroach mouthparts operate more like a sideways or lateral version of the bite mechanism of a mammal. Dobsonflies and some species of beetles that occasionally bite humans (usually in self- defense) have similar types of mouthparts. But since living humans are not targeted as a primary food source (like with some blood feeders), bites from insects with chewing type mouthparts are much less common.

The source of wounds can be difficult to identify without capturing the pests while they are causing the injury. This is especially challenging when diagnosing cockroach bites as they would most likely occur when individuals are asleep. Still, in residences with severe infestations, cockroaches should be considered as a possible cause for bite-like markings or small patches of abraded skin that show up after sleeping.9

The injuries or signs left as a result of a cockroach bite vary. Bites from Oriental cockroaches, Blatta orientalis, have been documented to cause inflammation and tissue necrosis.8 As previously noted, German cockroach bites can manifest as crusted ulcerations. On one disturbing occasion, an emergency room physician reported that he treated a handicapped patient who developed abscesses in skinfolds of her abdominal area from wounds presumed to have been caused by German cockroach bites.10 Finally, after the injuries have healed, scarring or other skin discoloration has been described in some cases.6, 7, 9

The good news is that despite their powerful mandibles, cockroaches aren’t known for antagonistic behavior. They will not run out aggressively and bite in a hostile manner. Still, in the right circumstances, they will gnaw on human skin and can cause injuries from this behavior. They may be enticed by food residue on the surface of the skin, or perhaps by perspiration, a wound or dead tissue. These conditions can result in them biting and injuring the area. On a large scale in the United States, these occurrences are rare, but the likelihood can increase in severely infested dwellings.

Josh Shoemaker is an entomologist focused on pests of public health significance. He has a master’s degree in entomology from the University of Nebraska and is presently working through a graduate program at the University of Missouri in public health.

References
1. Lee, C.-Y. (1997). Medical Importance of Domiciliary Cockroaches. Singapore Microbiologist, 11, 14–17.
2. Nuwer, R. (2015). A Cockroach Can Bite with a Force 50 Times Its Body Weight. Smithsonian.com.
3. Denic, N., Huyer, D. W., Sinal, S. H., Lantz, P. E., Smith, C. R., & Silver, M. M. (1997). Cockroach: The Omnivorous Scavenger. The American Journal of Forensic Medicine and Pathology, 18(2), 177–180.
4. Benecke, M. (2001). A brief history of forensic entomology. Forensic Science International, 120(1-2), 2–14.
5. Gates, M.F. (1912). Roaches and Their Extermination by the use of Sodium Fluorid (NaF). United States Naval Medical Bulletin. (Vol. 6, No. 1, pp. 212-214). Government Printing Office.
6. Nicols, A. (1870). The Cockroach. Nature (London), 3(58), 108–108.
7. Roth, L. M., & Willis, E. R. (1957). The medical and veterinary importance of cockroaches (Vol. 134). The Smithsonian Institution.
8. Kramer, R. D., & Brenner, R. J. (2009). Cockroaches (Blattaria). In G. R. Mullen & L. A. Durden (Eds.), Medical and veterinary entomology (2nd ed., pp. 43–57). Elsevier.
9. Uieda, W., & Haddad, V. (2013). Cockroach (Blatella germanica) bites in Amazonian indigenous peoples. International Journal of Dermatology, 53(4).
10. Mellick, L. (2014, April). Cockroach in the Ear [web log]. https://journals.lww.com/em-news/blog/M2E/pages/post.aspx?PostID=24.