Change Is A-Comin’

What am I looking at?

This is the larva of a midge in the genus Chaoborus, pictured in mid-metamorphosis under polarized light. The colors you see are body parts with different molecular characteristics that show varied hues under polarized light; muscles and collagens in particular, due to their fibrous nature, have a way of interacting with polarized light that produces vibrant colors. You can see the larva’s head in black and blue (1); its developing wings in orange, green, and purple (2); and the rest of its body also in orange, green, and purple (3).

Biology in the background

Chaoborus is a group of small flies in the midge family. They deposit eggs and develop in fresh water, undergoing four larval stages known as instars. The larvae are predatory; they eat a variety of small invertebrates – rotifers, water fleas and other crustaceans, and other aquatic insect larvae, including mosquitoes. They use modified, prehensile antennae to grasp their prey in a praying-mantis–like fashion.

The larvae of this genus are known as glassworms; they are big enough to be seen with the naked eye and are transparent. They have two pairs of air-filled sacs, visible as shiny metallic bubbles, that act as buoyancy organs and help them stay at their target depth. These larvae will continue eating until they grow large enough to pupate and transform into adult flies, when they emerge from the water to reproduce. The adults of this genus are commonly called phantom midges or lake flies and are nectar feeders – they don’t bite other animals or suck blood.

Midge larvae can vary in size quite a bit; the largest can grow up to 30 millimeters, or a little bit larger than the width of a human thumbnail.

Technique

These images were created using a form of light microscopy known as polarized light microscopy.