Figuring out what species something is can be fairly difficult, especially if you’re looking at insects – even relatively small insect orders are generally larger than other Animalia orders. For example, Plecoptera (stoneflies) are a relatively small order within the larger class Insecta, having roughly 3500 species. The order Rodentia, on the other hand, makes up over half of the class Mammalia at just over 2000 species. With so many species, it can be very difficult to narrow down your identification to even just a handful of relatives. That is, without looking at some more, erm, unsavoury parts. But more on that later. Let’s start more general.
Kingdom
Animalia.
Phylum
Arthropod.
Class
Insecta.
Order
This is where we actually have to do some identifying, albeit identifying of a relatively easy calibre. There are 32 orders of insects, which may seem daunting at first, but based on wing pair number and general body shape/size, identifying down to the order level is pretty easy to get the hang of. I suggest using the keys available from the American Museum of Natural History – Key A contains insects with well-developed wings and Key B contains insects with tiny or absent wings. You may be surprised, as I was at first, to find out that cockroaches have wings!
A phylogenetic tree of all known extant (aka not extinct) insect orders. The numbers on the diagram show us where major changes or separations are:
- All hexapods
- True insects
- Development of wings
- Development of wing folding
- Orthopteroid (grasshopper-like) insects
- Pan-plecopteran (stonefly-like) insects
- Acercaria insects (loss of cerci, etc.)
- Endopterygota (complete metamorphosis)
Spongymesophyll – Orders Tree – Insect Orders 2 (BugwoodWiki)
Family
Within each order, there are different families. Unfortunately, there are often more families in one order than there are orders within the class Insecta. For example, Coleoptera, the beetle order, has 166 families worldwide! Thankfully, there are also some very comprehensive keys available for more commonly collected insects. If you have a specific focus on one order, I would suggest finding or purchasing a book specific to that order (such as Flies: The Natural History and Diversity of Diptera) or Steven Marshall’s Insects: Their Natural History and Diversity, which is a great photographic guide (I would estimate that most of its pages are photographs of bugs) and also has flowchart keys with pictures that are very easy to use, even for amateurs.
All the pictures above are beetles – insects from the family Coleoptera. This family has an extreme amount of diversity, partially due to just having so many family members!
Ryan Kaldari – Kaldari Curculio occidentis 01 – Wikimedia Commons (CC0 1.0)
Fir0002/Flagstaffotos – Metriorrhynchus rhipidius02 – Wikimedia Commons (CC BY-NC)
Richard Bartz – Oxysternon-conspicillatum male – Wikimedia Commons (CC BY-SA 2.5)
Most identification at the family level is a bit more complicated than identifying to order. Instead of looking at general body or wing shape, we’re usually examining many different parts of the insect. It can be difficult to identify insects even just down to the family based on a photo if, for example, the hind legs or antennae are not quite in focus. When insects have been collected, use of a magnifying glass or even a dissecting microscope is generally required (especially if you need to update your glasses prescription like I do). Common identifying features include the following:
- Number of tarsal segments
- Type/shape of antennae
- Number of antennal segments
- Type of mouthparts
- Absence or location of spines on the legs
- Absence or presence of hairs on different parts of the body
- Venation in wings
- Shape of wings
- Shape of pronotum
- Absence or shape/size of ovipositor
- Absence or presence of ocelli
- Body shape
- Location of antennae on head
- Size of eyes and location on head
As you can tell by this short list, which is by no means comprehensive, identification can get more complicated and tedious the more specific you want to get when identifying. My least favourite order to identify is Diptera since there are so many small things you need to be able to pay attention to, but at least I’ve never had to identify them down to genus or species.
Definitions
Elytra – Hardened forewings found in Coleoptera and some Hemiptera
Extant – Currently living (i.e. not extinct)
Pronotum – A plate that covers all or part of the thorax, usually spanning from the head to the bases of the wings or elytra.
Ocelli – Simple eyes that some insects have in addition to their regular set of eyes. They detect movement through sensing changes in light
Genus and Species
This level of identification is not generally achievable for amateur entomologists, as the keys required become quite specialized and involve more subtle differences in morphology. For now, let’s get to the good stuff – how insect genitalia comes into the mix.
One way to tell different species apart is actually by looking at their genitalia, believe it or not. This aspect of identification is so helpful that there have been numerous studies on insect genitalia within different families and genuses to aid with identification. Additionally, there has been the invention of the phalloblaster, a device that will actually re-inflate an insect’s genitalia after it has died. What a time to be alive.
Generally used after insects are killed during collection (as opposed to use on dead bugs you find in your pantry or window sills), the technical term for this contraption is the vesica everter. You can read a peer-reviewed article about its operation here, but the general idea is that is that you use a very small needle to inject alcohol into the genitalia, which then makes it erect. This might sound like something fetishists do to get their rocks off, but the study of genitalia is often necessary to differentiate between similar, closely-related species. Plus, it’s very cool. In fact, Maria Fernanda Cardoso did a whole art installation on insect genitalia! You can see some great coverage of her work here.
Here is a close-up of the hind end of a male scorpion fly, Panorama communis. Believe it or not, this stinger like appendage is actually this insect’s genitalia! No phalloblaster required to study that baby.
Richard Bartz – Skorpionsfliege Panorpa communis male genital – Wikimedia Commons
(CC BY-SA 2.5)
While insect identification can be difficult at first, it has a certain knack to it and can become greatly rewarding. Goals for this week? Go out and find an insect (any kind!), then see how far you can get with identifying it using resources found online or at your local library. If you live near a university (or, even better, are a student), go in and take a look at some of their entomology textbooks to find pictures and keys. Don’t be discouraged if you don’t get very far – even just finding the order is something!
In the future, we’ll discuss some of the difficulties of insect classification and identification using ambush bugs as an example. It’s easy to tell who these guys are just by looking at them, but we run into more issues when we try to identify further than the family level.
Resources and further reading:
It’s all about the genitals: the secrets of fossil insects and amber (The Guardian)