Antennae – Two Scents Worth!


Mr. Bug.

Remember the old, metal “on top of the TV” antenna? What was it doing up there? Probing and sensing the living room air for signals sent from a distant giant tower, the “rabbit ears” somehow caught those invisible disturbances and transferred them to a “brain” in our black and white TV. That enabled us to listen and see Ed Sullivan introduce his latest find – an acrobatic team from Bulgaria who astonished us with jumps and twists and twirls. Could we smell these distant characters or taste them or predict their next move? Not hardly!

            Now consider Mr. Bug above. He carries his intelligence gathering “rabbit ears” around with him and can orient them in any delicious direction he chooses (Mr. Bug might be Mrs. Bug – not that I could tell the difference.) He can hear, smell, taste, and in a sense “see” his environment. The cavorting larva who is jumping, twisting, and twirling in front of him is profiled, identified, and perhaps even fingerprinted (in a bug way).  Mr. Bug’s eyes coordinate with the antennae input and before the larva can count to three, he becomes the victim of a rapacious assault.  Let’s look more closely at these things we call antennae.
            Different researchers group insect antennae into ten, twelve, or even fifteen different types. We will look at ten basic antennae and do it in two papers – five at a time.

The goal is to learn the basic antenna type associated with different insects to help with identification. Remember, antennae (plural form and my high school Latin teacher would be proud of me!) are on the “anterior” of the insect whereas “cerci” (see article 1) were on the “posterior”.

            The first grouping is the “setaceous” (sit-ta-shus) type with bristle-like protuberances either next to or below the eyes. They can be short or long and consist of equal sized segments called (ready?) “flagellum” or “flagellomeres”. Most flagella are progressively smaller as one scans from the base near the eye to the endpoint or in a “distal” direction. Keep in mind that the dictionary meaning of setaceous is “bristle-like”. Some good examples are found on the dragonfly, the leafhopper, and the grasshopper. Prepare to be amazed!

A Leafhopper. Look closely – Just below the eye.

Note the tiny setaceous antenna just below the eye. It is so small that flagella details are impossible to see. The short antennae are a distinctive ID of the leafhopper.

Can you determine why the dragonfly uses its eyes more than its antenna as sensors?

            Wow! This dragonfly has a very short bristle setaceous antenna adjacent to the bulging eyes. One wonders what possible stimulus could be detected with such a short appendage. Note the cerci at the posterior. The next setaceous example is the damselfly.

A damsel in distress? How many blue bugs can you name?

The damselfly has a pair of setaceous (see how easily you got accustomed to that descriptive word!) antennae poking straight overhead. This is a beautiful example!

We need a longer antennae example and we need to see the flagella. Here is a good prospect – a caddisfly.

This guy relies on his antennae to find a mate.

Look closely at the setaceous antennae. They consist of segments (flagella) gradually tapering distally and are of an equal shape which is an important trait in insect ID. One wonders if Mr. Caddis has just caught the scent of a receptive female posed seductively on a nearby twig.

Our next type of “rabbit ears” is known as a “filiform” antenna. The segments are nearly uniform in size and are usually cylindrical. Ground Beetles and Tiger Beetles are good examples.

Disturb the mulch and who should appear?

            Ground Beetles and Darkling Beetles have filiform antennae. See how the segments are of equal size when compared to the setaceous antenna which decreases in size as one moves away from the head.

My, what big mandibles you have, Grandma!

            This is the business anterior of the Tiger Beetle who is a welcome addition to the home garden. He is not named “Tiger” because of his stripes! His filiform antennae have uniform segments and originate below the eyes. “Better to find and eat you!” as the leaf foraging caterpillar bedtime story goes.

            Filiform means thread-like but our next set of antennae are like a string of beads – Moniliform. Our Moniliform guest is the notorious wrinkled bark beetle.

“I will have two, medium tree pizzas to go, please.”

Mr. Wrinkle has a perfect set of moniliform antenna. Each segment is almost spherical and an easy mode of identification.

Our next-to-last example is an easy one. “Serrate” antennae are saw-like and similar to your kitchen bread knife or the edges on a wood saw. A Click Beetle is a perfect example of a serrate antenna. One wonders if he saws his victims into edible pieces!

A Click in time, saves nine.

            Our last subject in this essay is the “pectinate” antennae. A good definition is “comb-like” or having divisions similar to the teeth of a comb. There are gaudy examples in the insect world and I could show you hundreds of variations but here are a few representative pectinate antennae insects. The first is a fire-colored beetle.

A fire-colored beetle by any other name, looks as red.

The comb-like structure is easy to identify and take a look at these examples.

Easy to identify, if you had a close-up photo.
Thy name is Vanity, O Bug.
Stay tuned for Channel Two News at 5.

All have pectinate antennae.

            Now is time for a quick review. I have presented for your educational pleasure, five different antennae types – Setaceous, Filiform, Moniliform, Serrate, and Pectinate.

Setaceous have bristled; Filiform are threadlike; Moniliform are bead-like; Serrate are sawtooth, and Pectinate are comb-like.

Antenna by design.

            Just by looking at the above drawings, can you pick out the five I have presented? You didn’t even have to read the type!

            We are well on our way to learning about insects. We know about the cerci on one end and the antennae on the other and you can see that an appreciation of both will lead to an easy way to make identification of good and bad bugs in the garden. Here is my parting shot – can you identify the type of antennae?


2 thoughts on “Antennae – Two Scents Worth!

  1. Sure do enjoy your postsl.

    Liked by 1 person

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