Spiracle on 34th Street

What am I looking at?

This is a section through the trachea of a dragonfly. The larger tube is the trachea (1). Inside the trachea we can see openings leading to many smaller tubes called tracheoles (2) as well as two tracheoles emerging from the top (3). Scroll through the next images to see the spiracles that allow air into the trachea.  

Biology in the Background

Insects and other invertebrates use different mechanisms for providing their cells with oxygen than humans and other mammals do. Mammals have lungs that transfer oxygen from the environment to red blood cells that then carry the oxygen to the rest of the body via the circulatory system. But insects like dragonflies don’t have lungs. Instead, they have a network of breathing tubes called tracheae that run throughout their bodies. These breathing tubes, composed of chitin, start at openings in the exoskeleton called spiracles, which allow oxygen into the insect’s body.  Each body segment has a pair of spiracles that are controlled by muscles. The network of tracheae also allows carbon dioxide produced by the insect’s metabolism to exit the body.  

This system of gas exchange is relatively inefficient compared to vertebrate respiration and becomes less and less efficient as the organism gets larger, imposing an effective limit on the size of insects and other arthropods. However, in the Carboniferous period (360 - 300 million years ago), dragonfly ancestors reached the wingspan of 3 feet because the concentration of atmospheric oxygen was estimated to be 35%, significantly higher than today's 21%.

These tracheae can grow up to 2 micrometers across in dragonflies, roughly 38 times smaller than the width of a human hair.

Technique

These images were created using confocal microscopy.