PART 2 – The cockroach as a host

WALTER  DIONI                    Cancún, Quintana Roo, Mexico

Keywords: Cockroaches, Periplaneta americana, digestive system, dissection, external morphology of Periplaneta, chemical control.

Read part 1 of this series.


  Cockroaches are endorsed by 350 million years of life on earth. They are real "living fossils", as an enormous amount of species have existed since the Carboniferous period with a persistence that demonstrates their successful and adaptable structure.

  The diversity and extent to which they are represented in that geological era clearly indicates that there was a long previous evolution of roaches that has left no vestiges. There are now more or less 3500 living wild species.

  Nevertheless, here we are interested mostly in those few species that have adapted to the world of the civilized man and to the human environment, becoming a plague detested by all housewives and owners of bars, restaurants, supermarkets and food depositories of all types; thanks to their fertility, adaptability to all kind of foods, and especially to their cryptic behavior that assures them of relatively few encounters with man.

01 - cockroache

       This picture clearly show why the cockroaches are capable of colonizing very narrow cracks in floors, walls and furniture.

They adapt easily to most of the chemical pesticides that where intended to control them, and they end up developing resistance to them. So the modern way for the safe control of cockroaches is turning out to be the old methods of physical control and the traditional papers covered with sticky substances.

 See the Appendix for some old but effective control methods.

 Throughout the world the species of cockroaches that have been successful in man's environment are Periplaneta americana, Blatta orientalis, Blatella germanica, Blaptica dubia, Suppella supellectillium, Suppella longipalpa, etc.

 Except for Blaptica dubia, from South America, the other four genera are perfectly adapted to Europe.

 In Durango (Dgo.) Periplaneta americana is common in the city, living mainly in the culverts. We suffered in Hermosillo (Sonora) the invasion of the house by Blatella germanica, and in Cancún (Quintana Roo) we have found up until now P. americana and Blatta orientalis.

 You do not have to be deceived by the name of Periplaneta americana. According to one author writing on the internet, the origin and dispersion center of this highly invasive species is Africa from where it arrived at the United States in 1625. Linnaeus, created in 1758 the genus Blatta in which he included the species americana (surely because the available specimens were from America), and Burmesteir in 1838 created the genus Periplaneta to hold americana.


 Readers who wish to see images of the different species, can make use of their favorite "search engine" including in the search the complete species name, written between quotes. Most of the web literature is related to the “pest” control, and companies offering their services.

03 - cockroache
04 -cockroach
Male, periplaneta, ventral view, approx. 3x natural size.
Female, periplaneta, ventral view, approx. 3x natural size.

Torrential rains of this season (June-July) force the roaches to leave their hiding places even in the daylight, terrifying the housewives that take care of their house hygiene.

The municipality collaborates in the control of the plague by fumigating with insecticide, with very little adoption of ecological criteria and techniques. This provided me with several specimens to illustrate this article. If I wanted I could have had dozens at my disposition.

06 -cocckroach
08 -cockroach
Periplaneta, head, frontal view
Periplaneta, head, ventral view

Whoever wants a more thorough in depth view on the world of cockroaches, including those species that some use as pets, like the sizzling cockroach of Madagascar, and other but smaller species that herpetologists raise as food for their other pets (lizards and snakes), can visit these Internet addresses:


The anatomy of a cockroach is a magnificent example of the structure of an insect. This explains why several educational pages on the internet describe it in detail. The best one by its didactic quality and beautiful macro and photomicrographic images, is this site of the University of Alberta:


 Also a very complete and descriptive site, but illustrated only with drawings, is the one of Prof. Fox, at the Lander University site:

 HTTP://www.to lander.edu/rsfox/310PeriplanetaLab.HTML

 The notes that follow will serve as a guide for those who wish to try the parasitologic investigation of a cockroach.

10 cockroach
The cockroach leg is not totally typical. Normally the coxa is a small segment and the trochanter an important one; a design that is inversed in this case.

Objections to dissection and justification of its use

If somebody has ethical doubts on this type of operation he can find an important discussion of this subject at:



Many very religious people and strict vegetarians by, for example imitating San Benito, walk with care to ensure they don't squash even an ant. But most of the non-religious or ideological objections have resulted in the avoidance of dissections in schools and colleges as they are considered cruel and in bad taste, (which according to my own experience at high school when 13 years old, is really sound). To avoid where possible the extent of animal suffering under experimentation, when that is inevitable in scientific research, suitable methods of anesthesia and euthanasia are used.

11 - cockroach
12 -cockroach
13 - cockroach
14 -cockroach
From upper left going clockwise: claw of the pretarsus in lateral view; pretarsus in dorsal view; a ventral view of the pretarsus. The three pictures show clearly the arolium, an adhesive cup that allows cockroaches to climb vertical walls, even polished ones. The fourth picture shows through the translucent chitinous skeleton the dense net of tracheae that oxygenates the powerful leg muscles.

  If it is desired to learn the principles of parasitological investigation, an important branch of general biology, agriculture,  veterinary medicine and human medicine, dissection is an essential practice. But you must master the correct techniques.

 In schools the use of real dissections (the specimens usually adopted are frogs, certain large locusts and cockroaches) can perhaps be replaced with great disadvantage of course by the use of virtual reality software or more modestly with three dimensional images of some good dissections,  or with drawings, based on the same source. This could probably save thousands of specimens used annually in schools.

 But it cannot be forgotten that the anatomy of the animals thus represented, which must necessarily be taught to the students, was discovered by scientists who made the necessary dissections and published the corresponding documentation.

 If Leonardo da Vinci and Vesalio had not dissected human beings, we would perhaps still believe that the veins and arteries (like the tracheas of the insects), were empty tubes that transported air from the lungs to body tissues. And without having learnt to dissect, no surgeon could save lives via a surgical operation.

 In fact we hope that some of the images presented here can be used with that aim. Aside from the images of the University of Alberta's website, the only dissection of a cockroach (in English) extensively mentioned on the internet is a promotion of a video tape, and is illustrated online only with small images, several of which are semi-concealed by a band of lines.

16 -cockroach
18 - cockroach
Female abdomen: note the acute end, the two sensitive cerci, and the short wings.
Abdomen, male: note the rounded end, the two anal stylets and the long wings.

The dissection

 Now we have the information we need to proceed with our cockroach dissection.

 For one complete, detailed and magnificently informed dissection, see the Canadian website referred to previously.

 Of course microscopists will not lose the opportunity to study the pretarsus of the legs that contains the secret of why cockroaches climb vertical walls, the structure of the trachea with its characteristic chitinous spiral support, the abundant fatty tissue in the abdomen, the structure of the compound eye of an insect with top lighting, the wings and antennae, etc.

 And, if a microscopist has hypochlorite, or even better sodium or potassium hydroxide, they may want to prepare the mouthparts of the insect.

 But here we will only give the directions to separate the alimentary canal, from which we will extract the parasites.

 According to the interests of the investigator the dissection can be made dorsally or ventrally. The ventral way is the easiest if you want to study the intestinal fauna, so it is the one to be used here.

 Of course if a representative research is to be conducted, enough male and female cockroaches, as well as nymphs, must be dissected to give a statistically significant sample.

 But for this article only a few adults of both sexes are used.

 Some authors assign to the adults of P. americana a length of up to 44 mm. In Cancún and Durango I have only been able to measure (on some tens of individuals collected) a maximum body length of 35 mm. Ten millimetres are significant when making such small insect dissections.

A list of the parasites I have found is:


Endamoeba blattae
Nyctotherus ovalis
Hammersmidtiella diesingi

Thelastoma  bulhoesi


 These species will be described in the following parts of this series. I heartly acknowledge the help of Professor Nora B. Camino, helminthologist at the University of La Plata, La Plata city, Bs.As., República Argentina, for the confirmation of the nematode genera to be  described here.


 Cockroach control

             If they are not a real nuisance, and if their activities are limited to the garden or the wild, leave them alone. In nature they have an important role in the disposal of ecosystem detritus. Use all your best efforts not to offer them a way into your house. A clean house, without many crevices, and without poorly stored food, rarely suffers from large cockroach invasions. Attempt to control them only if their populations increase beyond that of some occasional visible visits.

             The oldest and most efficient method is the use of boric acid crystal powder at sites near the places were cockroach retire and procreate. They eat the sharp crystals which lacerate and cause bleeding of the gut.

Boric acid bait

Note: do not breathe the powder, use rubber gloves to prepare the bait.

  • One half cup (350 grams) boric acid - looks like white powder and is available in pharmacies
  • one cup flour
  • two heaped spoonfuls of sugar
  • water

Mix boric acid, flour and sugar.
Moisten with just enough water to make a paste that can be formed into small cylinders or balls.
Make as many of them as you can. Distribute them in critical concealed places.

            Nowadays, with exactly the same rationale is the use of ground diatomaceous earth; not the powder for domestic pool filters, but the type sold by many garden centres to control insect pests. Broken diatoms have very sharp silica fragments.

             If this seems cruel, think of the insects (cockroaches and who knows what else) inmobilized by neurotoxic chemicals, condemned to die of dehydration and starvation. And of the collateral effects of this type of insecticide on the whole ecosystem.  Such methods kill not only cockroaches, but any insect within its reach, and has accumulative and deleterious effects on birds and rodents that eat the carcasses.

Comments to the author, Walter Dioni , are welcomed.


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