The prementum and other insect mouthparts

An Aeshnidae naiad with its prementum (red arrow) displayed for the purposes of this discussion. Normally it is folded tightly against the body.

The destination and journey are equally important!

The labium or lower jaw section of a naiad covers
other mouthparts.

When I was in high school, I would go to the California Academy of Sciences and spend the day there at something called the Student Section. At that time, I had access to our own collections and there were plenty of opportunities to help the curators and visit with well know biologists. I am sure that opportunity is absent since it became a theme park. (Argh!)

I specialized in two taxons, birds and mammals, and they still are my favorites. However, I worked along side folks who specialized in a wide variety of organisms including, marine invertebrates, reptiles, amphibians, and every other organism group. Because of this, I discovered I like any wild animal I meet and each time I spend time learning about an organism I have a deeper understanding of the complex nature of ecosystems.

These experiences are responsible for my approach to the research I am doing. Specifically, although the destination, the diet of the Western Pond Turtle in an urban setting, is important, so is the journey to the destination. Specifically, equally important is the knowledge I acquire and the so-called tangential observations I make. The knowledge improves my awareness of the components of the ecosystem and helps develop broadly applicable concepts. Further, it makes it easier to communicate with the specialists while doing research. For example, the focus of my classwork during graduate school is learning more about the landscape and climate processes. Therefore, I took classes in the geography and geology departments so I can better understand the role of these abiotic (non-living) forces.

Therefore, if I am going to write about the mouthpart of one organism, the prementum of a dragonfly naiad, I am going to learn about he mouthparts of all insects. At the same time, I will enfold in into my existing knowledge of evolutionary processes (i.e., adaptive radiation). Of course, I also will spend time looking at the evolutionary history of this organism.

Consequently, I examined all the basic kinds of insect mouthparts, their evolution, and how the different insects use them. 

Insect mouthparts

Insect mouthparts fall into two broad categories and some have features of both.  First, there are mandibulate insects (i.e., dragonflies, grasshoppers, and ladybeetles), they eat solids, plant or animal or plant matter. Second, there are the sucking insects haustellate (haw-stell-ate) insects that have sucking mouthparts (i.e., mosquitos, moths, butterflies, and blow flies). Lastly, there are those that have elements of both such as bees. The have mandibulate elements to grind pollen and wax and sucking mouth parts for getting nectar.

Insect mouthparts include five basic elements:

·      Labrum- an upper lip the holds food

·      Mandibles-they crush and grind food

·      Maxillae- they manipulate the food much as we use a knife and fork

·      Labium - including the postmentum, prementum, palpi glossae, paraglossae, and ligula. 

·      Hypopharynx – it is used to mix food and salivary secretions but absent in naiads.

Many of these elements are so modified during the evolution of the insect that they are not easily recognizable.

Basic mouth parts of the Aeshnidae naiad. Note the hooks at the distal end of the prementum and the large muscles for shooting the prementum and hooks forward and quickly withdrawing them.

In this ventral view of the naiad's mouth you can see the maxillae for manipulating food and behind them are the mandibles for side to side chewing. The rim of the labrum is visible as well.

The Aeshnidae naiad

A ventral view of the naiad showing the maxillae that manipulate the food (red arrow) after the prementum has captured the prey.

Imagine for a second you are a small fish or tadpole swimming in a drainage ditch connected to Santa Rosa Creek. As you nibble away the day a silent predator is prowling the waterway, sometimes swimming in open water and other times moving through the emergent vegetation. You see it but it is not moving and almost 10mm away and you feel safe. Just as you down a juicy tidbit of food agonizing pain strikes both sides of your body because you have been impaled by the hooks located on the prementum of a naiad. Your life is over!