We all know humans (and other mammals have brains), but sometimes we don’t consider that other animals have brains, too–even invertebrates! This will be a short post about insect brains. I may pick up on this topic again at a later date.

Manduca sexta larva

Insects also have neurons.  These neurons compile into groups called ganglia (singular ganglion). In our Insect Structure and Function course, we dissected Manduca sexta larvae (tobacco horn worm) to look at their nervous system.

We counted the ganglia from the head to the abdomen. They were white-ish and diamond-shaped, linked by connectives. The subesophageal ganglion is a very important one, but we’ll cover that another day.

An insect’s nervous system has many functions–sensation, movement, release of hormones, and all that fun stuff.

This website has some pretty good information. If you mouse over the underlined words, it will show them in red on the image of the ganglia/nerves on the left side of the page. Very neat.
For slightly more basic information, visit this website.

I may go into more detail another day about the neurological and hormonal controls of different behaviors such as ecdysis (molting) and flying.

But for now I want to make the point that insects have brains, too.

Here is an obligatory blog post about Antarctic midges (Belgica antarctica Jacobs). They live in the Antarctic. The end.

Just kidding! I’ll write more.

Well, this midge (Diptera: Chironomidae) is purely terrestrial–although it does get soaked in water an awful lot–the largest terrestrial animal in Antarctica! (Penguins aren’t purely terrestrial).  Living in Antarctica, this midge encounters a wide variety of environmental conditions. One would think the worst would be in the winter, but summer can be the harshest.  This is because the weather patterns so quickly change, especially in the microhabitat of the midge larvae. (They spend most of their life in the larval stage.)  In the summer, the larvae are very likely to come into contact with both seawater (tidal sprays) and freshwater (melting snow.) The water often evaporates, which can create a dry microhabitat or a hypersaline environment. The midge must find ways to deal with all of these. In hypersaline conditions, the midge must osmoregulate. Osmoregulation is a physiological response to handle these harsh conditions. This involves the release of osmolytes into the hemolymph and a reduction of water loss. The compounds released into the hemolymph not only affect osmosis, but they can also change the supercooling point (the temperature at which a solution freezes)!

Belgica antarctica larvae are also capable of what is called rapid cold-hardening. Cold hardening is a physiological process by which an organism adjusts to be able to tolerate colder temperatures.  It may also increase freeze tolerance! which means they can handle being frozen. (Yes, some of their tissue crystallizes and they come out alive! Freeze it too cold or too long and that might not be the case.) Some insects are freeze tolerant, and some are not. Crickets do not handle freezing very well.

In the winter, the midge needs to tolerate the cold. The larvae are quite freeze tolerant (to about -15°C). Another mechanism the midge larvae use to survive the winter is cryoprotective dehydration. This process also involves the production of osmolytes and their release into the hemolymph. The organisms slowly dries out in sync with the vapor pressure, so the melting point of its liquids is the same as the ambient temperature, which prevents it from freezing.

Pretty neat, no? Think you’d want to go to Antarctica to research these creatures?

A few references:
Elnitsky, M. A., J. B. Benoit, G. Lopez-Martinez, and D. L. Denlinger. 2009. Osmoregulation and salinity tolerance in the Antarctic midge, Belgica antarctica: seawater exposure confers enhanced tolerance to freezing and dehydration. Journal of Experimental Biology 212: 2864.
Elnitsky, M. A., and R. E. Lee. 2009. The rapid cold-hardening response in insects: ecological significance and physiological mechanisms, In L. Gusta, M. E. Wisniewski and R. Trischuk [eds.], Patterns of Freezing in Plants: The Influence of Species, Environment and Experimental Procedures. CAB International, Oxfordshire, UK. pp. 240-248.
Elnitsky, M. A., S. A. L. Hayward, J. P. Rinehart, D. L. Denlinger, and R. E. Lee Jr. 2008. Cryoprotective dehydration and the resistance to inoculative freezing in the Antarctic midge, Belgica antarctica. Journal of Experimental Biology 211: 524.