What’s in a name?

2009-06-18 00:00

WHEN is a fly not a fly? This is not a trick question, but a fitting title for a chat about terminology. As a scientist, I know just how confusing common names for animals and plants can be.

While scientific names may be strange and sometimes difficult to get your tongue around, they have one huge advantage — they do not often cause confusion. To illustrate this, let’s take the word “fly”. When used correctly, this is a general term used for any insect that belongs to the insect order called Diptera. This scientific name is derived from Greek and means “two wings” — and so almost all insects possessing a single pair of wings are true flies.

I say “almost” because, as we all know, there are usually exceptions to all rules. So, common names such as crane fly, horse fly, robber fly, bee fly, hover fly, fruit fly, house fly and tsetse fly, etc. clearly refer to two-winged insects of the order Diptera. No problem so far. However, problems rear their ugly heads when names such as those that follow are used: greenfly, mayfly, damselfly, dragonfly, stonefly, hangingfly, butterfly and firefly, etc. None of these belong to the Diptera order and so are not true flies.

You may have noticed that I have used two words (e.g. horse fly) when talking about true flies, and only one (e.g. dragonfly) when talking about things that are not true flies. This is a fairly commonly used protocol that I wish was universal as it does help the amateur learn the subtleties of terminology that are well understood by specialists.

So, how would you identify a true fly? Simple, you say, just count the wings. Okay, how many wings can you see in my photo (far right) of a mayfly (order Ephemeroptera)? Not so easy is it? In this instance the insect holds its wings vertically above the body, and on first inspection you would probably say it has one pair of wings. However, mayflies have greatly reduced hind wings that can only be seen if you catch the insect and look at it with a good magnifying glass, or better still, a microscope.

By the way, mayflies can be fairly common in our concrete jungles, especially if you live near a flowing stream. In their immature stages, mayflies live aquatic lives and may take a year or more to reach the adult stage. The adult emerges from the water and flies off to mate and, in the case of females, to lay eggs. They are called Ephemeroptera because they are ephemeral — meaning, they do not live very long. Adult mayflies do not feed and can live for as little as one day.

What would you say the weird-looking insect in my other photo is? Although you can’t see the wings clearly, the average person might think that it may be some kind of wasp — and that might be a reasonable guess as these things do resemble some wasps. It is actually a true fly, a robber fly of the genus Pegesimallus. These do not look like any of the flies people usually associate the term “fly” with — things like house flies, horse flies and dung flies. But, believe me, it does have only a single pair of wings, while wasps have two pairs.

These long-legged robber flies can be quite common in suburban gardens, where they feed mainly on small beetles.

Now, if you think the problem I’ve highlighted is confined to the term “fly”, think again. Beelice are not lice, but flies; booklice are also not true lice; whiteants are not ants, but termites; and water crickets are bugs, as are Christmas beetles and water scorpions. Ladybugs are not bugs, but beetles, and mealworms are beetles, as are tobacco slugs. Bloodworms are flies, glow-worms are beetles, while bagworms, cutworms and inchworms are all moth caterpillars.

Now that you are completely bamboozled, I think you might agree with me that terminology can often be very confusing.

 

• Dr Jason Londt is a natural scientist with a special interest in entomology. He welcomes queries and comments, which can be sent to him at jasonlondt@telkomsa.net Please do not send large attachments.

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