Surprisingly, glass worms (Chaoborus crystallinus) are not worms at all, they are white mosquito larvae (phantom midge larvae), and the fly they transform into is a so-called non-biting insect (gnat).

In my area glass worms are most readily available, through my local pet shop, in the winter time. The larvae are transparent in appearance giving a spooky look. They are usually half an inch in size and have two black dots in the body (which can be seen). Surprisingly these black dots are actually air sacs that work like a swim bladder.

Glass worms usually swim in a horizontal manner and the air sacs inflate and deflate to move up and down in the water. The larvae breathe through the end of their abdomen and have two eyes at the front of the body, with a claw protruding as if ready to grab something or hook onto it. The claws can be used to grab smaller creatures (especially small fry), so feed cautiously if very small fish or fry are present in your aquarium. The claws are actually hinged antennae which can be snapped together, thus giving the appearance of claws.

The size of a glass worm can vary from half an inch to almost two inches in length (frozen and live). Your fish should love these easily digestible 'see-through' worms because of the chase and kill or chase and swallow opportunities they will get.

I don't know the exact timing as to when the flies mate in the U.K. bu ...

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