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 sacks that work like a swim bladder.
Glass worms usually swim in a horizontal
manner and the air sacks 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
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. but in other temperate areas adult flies emerge and mate in June/July.
When the larvae pupate and grow into the mosquitoes the females lay eggs in jelly-like
discs on the surface of the water. The larvae then hatch out and start wriggling
about in the water.
Glass worms can be found in ponds hanging horizontally
(usually) but you must look very carefully because, due to their transparent appearance,
they are difficult to spot, and it is usually movement that makes them appear
There are two opinions of the hatching process and development
stage of the larvae:
1. Because the glass worms are the young stage of the
fly, it won't take long before they change into pupae and complete their life
cycle by transforming themselves into flying mosquitoes. This transformation process
can take up to three weeks, so the amount of time they will be available for fish
food is limited by the timing of their life cycle.
2. But according to the
Offwell Wildlife Trust (Devon) after mating the flies
(who live for about
ten days) lay eggs as soon as possible and these eggs quickly hatch. Larval development
will take about a year so the larvae (glass worms) will be around all winter.
I am able to obtain glass worms in the winter time, via the pet shop, I would
be in favour of the Trusts opinion and perhaps option 1. applies to larvae in
other temperate areas?
While studying at Shipley College in Bradford I recall
meeting an American gentleman called 'Todd', in the college library. We became
friends and, in conversation, he mentioned that he had seen glass worms in ponds.
He also told me how his father-in-law had a preference for feeding glass worms
to his fish, how he kept these worms in a refrigerator, believed the larvae to
be hardy and had known them to recover from being frozen for short periods.
I am not sure if glass worms in the U.K. could survive in frozen ponds but perhaps
this could be the case in other geographical areas?
The local pet shop owner
told me that his previous live food supplier had informed him that:-
Glass worms can survive in water that has not been treated with de-chlorinator.
So if you place them in water not treated for chlorine they will still survive.
He had read an article in which brine shrimps and glass worms were laboratory
examined to see which had higher protein levels - glass worms won.
appearing empty and transparent glass worms helped to stimulate colours in live
stock to which they were fed.
4. Glass worms can live for a couple of weeks
or more in coldwater. This would be useful to we aquarists' as it would allow
us to keep our stock of glass worms alive a little longer for extended feeding
to our fish. Of course we would need to make regular water changes to any container
housing glass worms either indoors or in a fridge.
If I had met this supplier
would have asked the question 'Why are glass worms only available during the winter
time and not on a regular basis'? To answer my own question I assume the following
a. Glass worms are imported into the U.K. from other locations
thus their life cycle timings are different?
b. British glass worms may
be smaller in winter thus not pose the same predatory threat when fed to small
fish as they would at a larger summer size.
c. Suppliers may turn to glass
worms at a time of the year when other regular live foods, e.g. daphnia, are unavailable.
Frozen glass worms, sold as 'White mosquito larvae' are relished by my fish just
as much as the live form.
Finally I have heard mixed views about glass worms
e.g. some aquarists' say they are nutritious whilst others believe this not to
be the case. Regardless of these opinions if your fish or other live stock loves
glass worms then keep on feeding them. As responsible aquarists' you should give
your fish a well balanced and varied diet.
By Majid Ali, Ryedale
Thank You Majid Ali for allowing us to use your article.