After discovering the air passages or trachea were visible through the exoskeleton, I decided to look for other internal features.
What about the dark green line in the middle of the back? (Photograph was taken looking down at the caterpillar.)
You might think that was the intestine, but I happen to know that the “heart” in insects is a long tube running through the dorsal surface (back). Could that be the “heart?”
Let’s take a look at this video taken from the perspective looking down at the caterpillar from the rear. Watch the green line.
If you look closely, you should be able to see the vessel expand and contract as hemolymph (the insect version of blood) is pumped through.
You might also notice that the pumping is not regular. It starts and stops.
The circulatory system in insects consists of a long tube called the dorsal vessel. The part running through the abdomen is designated as the heart.The aorta is located in the thorax and head.
Unlike ours, it is an open system. The hemolymph bathes the tissues inside the insect. When the heart pumps, the hemolymph moves into the dorsal vessel from the posterior or rear of the caterpillar and flows toward the head end.
In the dorsal vessel are openings known as ostia. Depending on position and type of insect, the ostia may be “incurrent” (hemolymph flows in) or “excurrent” (hemolymph flows out).
The hemolymph that exits goes back into the tissues, carrying in nutrients and moving away wastes.
It was pretty cool to see something I’d learned about in textbooks pumping away in real life.
You never know what you might discover by looking at a plant. For example, while I was waiting for someone I looked at a shrub in front of a store. I saw signs of caterpillars, so I looked closer.
This leaf was rolled up. It looked suspicious. I decided to take a look inside.
There was a small green caterpillar.
It turns out it wasn’t the small green caterpillar I was expecting. The one I was expecting has a black head capsule. This one has a light-colored head capsule.
That warrants keeping an eye on it to see what it turns into. I put some leaves into a container with some moist paper towel.
Within a few days the caterpillar more than doubled in size. Its exoskeleton is so clear, you can see what it has been eating.
Let’s look closer.
Can you see the white lines that look like tree branches? Those are the tubes that carry air (oxygen) into the caterpillar’s body.
The tubes are called trachea and they originate at the round openings in the caterpillar’s sides called spiracles. We usually can’t see the trachea because the exoskeletons of most insects contain pigments that block our view.
This see-through caterpillar probably turns into a pyralid moth. With some luck, we’ll find out what kind in the next few weeks.