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How to identify cockroaches

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*How to identify cockroaches*

By George Beccaloni (Curator of cockroaches and other orthopteroid insects at London's Natural History Museum), 2016

Identifying cockroaches is often difficult, even for experts, especially if it is a dull coloured species with no distinctive markings which belongs to a group of very similar looking dull species with no distinctive markings and little variation in size or shape... Male genitalia may have to be used to provide a definitive identification, although genitalia are not useful for some groups e.g. hissing cockroaches (Gromphadorhini), as there is little or no variation between the species of the group. Specimens bred in captivity may be more difficult to identify than wild-caught specimens, since their colour and markings may be 'abnormal' due to artificial selection or genetic drift. Note that it is often very useful to know where the specimen or culture stock came from in the first place as this can narrow down the list of possible species - see below. It is also useful to know what family or subfamily the cockroach is before starting to try and narrow it down to genus or species.

If there are no books to the cockroaches to the region the species is from ("A Guide to the Cockroaches of Australia" by David Rentz is one of the few available), then try the following:

If you don't have a knowledgeable neighbourhood cockroach expert who can help (and you're not really likely to as there are only a handful of such people in the world!), then post a good clear close-up image of it on one or both of the following Facebook Groups: https://www.facebook.com/groups/blattodea/ and https://www.facebook.com/groups/621091044683934/ These groups have members who are expert cockroach taxonomists, so it is possible that they may recognise it.

If this draws a blank, and if you have some entomological/taxonomic knowledge, then you could try the following:

1) Go to the online world catalogue of cockroaches i.e. the Cockroach Species File (http://cockroach.speciesfile.org/HomePage/Cockroach/HomePage.aspx).

2) Click "Search" at the top, then click "Complex Search"

3) Type the name of the country (e.g. "England"), state or island (e.g. "Borneo") where the specimen was collected into the box labelled "Place name from geographic hierarchy" and then click "Find Place". If the place is found it will appear in the "Geographical Levels" below. Now click the "Submit" button at the bottom of the screen and all the cockroach species currently known to occur in that area will be listed. Click on one of these names to go to the record for that species. Note that this search only works for islands, countries, states and provinces (of large countries such as Brazil) - so don't enter anything more specific e.g. "Sydney".

4) If you are lucky there will be a photo of one or more specimens of the species, which you can then use to compare your specimen with. Use the back button of your Web Browser to return to the species list you generated for the place name you entered, and check the records for the other species too.

5) If there are no specimen images then you may have to then try and obtain the original research articles in which the listed species were named, as these will contain descriptions and hopefully illustrations of the species in question. Many of these publications (especially older ones) are now available as pdfs on the Web. Here is a good way to find them: Go to the record for a species and you will see a list of "Citations" to research articles about the species in question. The citation at the top of the list (the oldest one) will contain the original description of the species. The default view of references in the CSF does not display the titles. To see them click on "Taxon hierarchy - Change items displayed" near the top of the screen and then select Yes for "Use long form display (titles and unabbreviated journal names for cited references, also differences in other places)". Next click on "Apply the specifications listed above" and the titles of the papers will now be displayed. Next, select all or part of the title of the article at the top of the citation list and paste it into Google Search, putting quotes around it to make the search results more specific (e.g. "On some Orthoptera from Porto Rico, Culebra and Vieques Islands"). Hopefully you will now be able to find and download a pdf of the article.

The geographical search can be used to produce lists of the cockroaches found in regions such as West Africa, which can be extremely useful when trying to identify species. For example, if you have a blaberid cockroach from Nigeria, it may not have been recorded from this country in the literature, but it may have been recorded from a nearby country. It would be tedious to have to go through species lists for each country in the region individually, but you don't have to - simply select the continent in "Geographical Level 1" (in this case "Africa"); then select the general region in "Geographical Level 2" (in this case "West Tropical Africa"). Then click the Submit button and you'll get a list of the cockroach species recorded from that region. You can restrict the search to a particular family etc. by using the "Scope of search" function at the top. This will enable you to (for example) get a list of just the Blaberidae known to occur in Africa. Please note however, that the "Scope" function currently has a bug in it which means it works the first time, but it then gets 'stuck'.....

Good luck!

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Male genitalia may have to be used to provide a definitive identification, although genitalia are not useful for some groups e.g. hissing cockroaches (Gromphadorhini), as there is little or no variation between the species of the group.

Don't you think the fact Gromphadorhina portentosa, Gromphadorhina oblongonota, and so-called Princisia varieties readily hybridize in captivity is a bigger barrier to identification of these from captive specimens? I wonder if there will be anything pure left in a decade.

Nice to see you on the forum.

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I am not 100% convinced that those species do hybidize, but they might - especially given that the male genitalia of hissers is similar or identical between species (so the 'lock and key' mechanism preventing hybridisation wouldn't prevent mating). The thing is that there is so much confusion about how to identify hisser species that some people are calling specimens Princisia when they are simply a dark form of G. protentosa. It would therefore not be surprising if they found that these dark individuals successfuly mated with a light form of portentosa... I think that well documented scientific studies need to be done to prove (or disprove) hybridisation - e.g. put one male and one female nymph each of different species together and rear them to adulthood and see whether the female produces young. Rear these young for one or two generations and preserve (in 80% pure ethanol) all the adults (including the original parents) for future study. Do you know whether anyone has ever done this?

PS. Although the three species you mentioned may (possibly) interbreed in captivity, in Madagascar they are geographically separated and don't seem to overlap. Wild-caught individuals are easily identifiable to species - so I would still regard them to be 'good species'. It is possible that the lack of overlap in the geographical ranges of the species has meant they haven't evolved barriers to mating.

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I am not 100% convinced that those species do hybidize, but they might -

You identified specimens I mailed you a while back and specimens from those stocks have hybridized in captivity. I documented hybrids of so-called princisia black and white with G. portentosa with photographs ten years ago in an article and I have been trying to make people aware of the importance of keeping stocks apart. I was given a mixed hybrid culture of G. oblongonota and so-called princisia big some years back. The G. oblongonota were identified by you and I'm sure you are familiar with the princisia big. I destroyed the portentosa/black and white hybrids but kept the oblongonota/princisia which is interesting in the moderation of the pronotum formation after a few generations (the shape looks more like G. portentosa than either of the founding 'species'). I'd be happy to send you some specimens if you like.

Unfortunately hybridizing these takes zero effort and is more difficult to prevent than to do. Young hissers often end up in the wrong cages even for keepers who consciously try to keep them apart. I've seen colonies with obvious hybrids over the last ten years from different hobbyists who did not notice one had gotten in the wrong cage.

I understand your hesitation with the state of identification of these species but some of these strains have unique phenotypes that are not followed by the hybrids. Obviously offspring of G. portentosa and princisia black would be difficult to differentiate since they aren't really a different animal (and princisia black are also often called grandidieri black).

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I saw a good comparison someone did some time ago, but now can't find it. It's annoying how images on internet forums disappear..

Forum photos are usually posted on external image hosting sites because forums have limited space. When I post a photo I try to make it small and post it directly to the page. Here is an adult male hybrid of a tiger hisser and normal G. portentosa hisser 2007.


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