What are Insects Like on the Inside? Vol. 7, No. 16
Brazilian skipper caterpillars, a.k.a. canna leafrollers, are transparent creatures. Like all caterpillars, their motives are clear. They just want to eat. But their glass-clear skin sets them apart from other caterpillars and gives us an uncommon view into their inner workings.
You may have noticed that insects are not made like us. For one thing we are bigger and warm-blooded. We have an internal skeleton that provides structure and support for our bodies and points of attachment for our muscles so we can move; insects have an external skeleton. We also have lungs that take in air and transfer oxygen to our red blood cells and a closed circulatory system with arteries and veins that transport oxygen, nutrients and wastes to and from cells throughout our bodies. Our hearts are in the front part of our chest and our spinal cord runs along our backs, so we have a ventral heart and a dorsal nervous system.
Insects have a dorsal heart and a ventral nervous system, and their circulatory system is not closed like ours. Insects do not have arteries and veins that carry their blood, nor red blood cells that carry oxygen. Instead, the blood, or hemolymph, flows inside their body cavity between and around the various organs. Their heart, or dorsal aorta, runs right along the back and pumps to move the hemolymph. Hemolymph is taken in through inlet valves along the sides of the dorsal aorta, pumped forward and out the end of the aorta near the head. See that dark green band that runs along the center of this caterpillar’s back? That’s the dorsal aorta. On live caterpillars you can watch it pump.
The thing that shows up best inside this caterpillar is its respiratory system. Insects breath through small holes along their sides, called spiracles. Those eight small white spots along the side of this caterpillar are the spiracles. There is another white spiracle on the darker, non-transparent segment located just behind the head. The white, thread-like structures branching away from each spiracle on the inside of the caterpillar are called tracheae. Tracheae are hollow tubes that branch into smaller tracheoles, which become smaller and smaller to carry oxygen directly to the various cells in the body. Much like a clothes dryer hose or vacuum cleaner hose, tracheae and tracheoles have ribs or rings that keep them from kinking or collapsing.
The white line that runs from spiracle to spiracle just inside the body is the longitudinal tracheal trunk, which is somewhat similar to the A/C duct system in a building and helps ensure even distribution of air within the body. Insects take in and expel air through their spiracles, through body movements that compress and decompress the tracheal system, forcing air into and out of the body, and they can open and close their spiracles as necessary. Larger insects, like grasshoppers, have air sacs associated with their tracheal system that increase their ability to move air in this way. Insects don’t have lungs, but they do breathe.
See Bug’s Eye View No. 21 of 2019, Cicada Exuviae , for more information on the insect exoskeleton and how it differs from our internal skeleton.
Blake Layton, Extension Entomology Specialist, Mississippi State University Extension Service.
The information given here is for educational purposes only. Always read and follow current label directions. Specific commercial products are mentioned as examples only and reference to specific products or trade names is made with the understanding that no discrimination is intended to other products that may also be suitable and appropriately labeled.
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