By Dr. Robert Norman, Clinical Professor, Dermatology, Nova Southeastern University
On a clear January day, I was on an exploration with my co-naturalist friend Ed when I spotted a monarch caterpillar on a wooden banister of a small bridge over a creek. I watched as the caterpillar used its antennae, one side at a time, to judge its location and keep moving forward. Watching a creature in the wild like this can be spectacular.
And it brings up many questions.
Do all insects have antennae? How can they feel through the antennae? What are the parts of an antenna? Do antennae allow getting Netflix or Amazon Prime or perhaps the Nature Channel for free?
How do we humans traverse our environment without these appendages on our heads?
Antennae are paired sensorial appendages located in the anterior parts of an insect’s body. Except for chelicerates (spiders, scorpions…) and proturans (non-insect hexapods), all arthropods—either crustaceans, hexapods (diplurans, springtails -Collembola- and insects), myriapods, (centipedes and millipedes), and the extinct trilobites—have antennae when adults.
Antennae are microscopically covered with hair-like sensilla. The sensilla are not related to the hairs found in vertebrates. Instead of keratin, they are made of chitin, as is the rest of insect’s cuticle.
Two major different types of sensilla exist. Chemoreceptorial sensilla have an inner channel through which suspended molecules such as pheromones enter. Mechanoreceptorial sensilla are retractable. Able to move at the slightest pressure or positional change to the ground or surface, they are also called proprioceptor sensilla.
Inside and in the base of sensilla live sensorial neurons connected to the insect’s brain. The specific brain region is known as the deutocerebrum. In chemoreceptorial sensilla, molecules bind with specific receptors that send nervous signals to the antennal lobe via the sensorial neurons. This antennal lobe acts similar to the olfactory bulb found in vertebrates.
The three basic segments of insects’ flagellate antennae are the scape, the pedicel, and the flagellum. The scape is the basal segment and articulates with the insect’s head. It is the only one that has its own set of muscles and is mounted in a socket called the torulus. The pedicel follows the scape and contains the Johnston’s organ, a collection of sensory cells. The flagellum is the remainder of the antennal segments. Individually known as flagellomeres, each is connected by thin membranes that allow them to move as a whole despite not having muscles.
Insects taste, smell, touch and communicate in part through antennae to gather information about food sources, potential mates (pheromones), enemies, dangerous substances (e. g. a poisonous plant) and nesting places. Antennae aid in migratory routes, as in the case of the monarch butterfly. Other parts of the insects, such as legs, palpi, and even the ovipositor (organ for laying eggs) may have sensorial cells.
Monarchs have what appears to be black antennae on both ends of their body. The ones in the front are antennae and the ones in back are to confuse predators.
As far as humans and touch, I am currently writing about that subject in one of my new books, and I will use comparisons and examples from the animal world.
How can you see the wonders of antennae in the wild?
The sure-fire answer is to get off the computer and phone, turn off the TV, and get out in The Great Florida Outdoors.
References https://allyouneedisbiology.wordpress.com
Dr. Norman is an advanced master naturalist graduate of the FMNP program from UF and a board-certified dermatologist based in Tampa and Riverview. He can be reached at 813-880-7546.
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