“I’ve found this transparent worm in my terrarium after two months of setting it up”, writes Thomas about the near-transparent, worm-like creature pictured below. “It’s a closed terrarium and I sometimes open the lid for ventilation because of fog buildup. I’m living in Hong Kong and at the time of discovering this worm, it was winter, with temperatures around 12°C to 20°C. The worm appears to have a black head and is not moving at all. It measures around 1 to 1.5cm in length. Is this worm harmful to my plants? Why does it suddenly appear in my terrarium? The plants I used are all free from pests as they come from nurseries. Thank you.”
To answer Thomas’ question right off the bat, we believe he is finding fungus gnat larvae in his terrarium. Fungus gnats are a type of fruit fly, and are considered household pests as they tend to infest houseplants (such as those in terrariums) and feed on decaying plant matter and fungi present in the soil. When their numbers are low, they do not pose much of a threat. In fact, their presence can be beneficial, as they help clean up dead plant matter and eliminate potentially harmful fungi. That said, when their numbers grow, they can prove harmful to the plants. Once their numbers grow to a certain extent, the larvae start feeding on young plants’ roots, thus stunting, if not preventing, their growth.
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So, how did these get in Thomas’ terrarium? It is likely that an adult fungus gnat flew into the terrarium when Thomas was ventilating it, and laid eggs in the top layer of the soil (which is typically where they lay their eggs). Now, given that the larvae he has found so far are not moving, it is possible that they died upon hatching, though we are not entirely sure why that would be, given that the conditions and habitat are ideal for their survival. We will also say that the shape of this particular larva pictured above is a bit strange: it looks almost like it has been mangled by something. But since Thomas has not mentioned the presence of any other animals inside the terrarium, we will assume there would be nothing inside it to mangle to the larvae, and that it simply looks like. Taking all of this into account, we must acknowledge the possibility that these are not fungus gnat larvae, but something else. In any case, cleaning out and replacing the soil might be a good idea, so as to get rid of whatever organisms are present.
To conclude, we think that the translucent worms Thomas found in his terrarium are fungus gnat larvae. Since they appear to be dead, he does not need to worry much for his plants’ health, but it is still a good idea to clean them out, as leaving decaying or dead organic matter in a terrarium is not a good idea, as it can invite other problems. We hope this helps, and we wish him the very best!
All About Worms is always free, always reader-supported, we don't subject you to ads or annoying video pop-ups. But it does cost us money out of our pocket to keep the site going (nearly 20 years so far!) So your tips via CashApp, Venmo, or Paypal are appreciated! Receipts will come from ISIPP Publishing.