“Worms with Shells” are Case-bearing Moth Larvae

Today, we will discuss an email from a woman who has found an unusual creature in her room. She describes the creature as being less than an inch long. She also says that it has a single black line around that head, which she describes as black or dark brown. The oddest thing, she says, is that seems to be carrying some sort of shell with it. This shell appears to be hairy and looks a bit like a cocoon.

She sent us some pictures but was unable to get a very clear shot because the little critter hid when she got too close. Our reader is not worried that the critter is dangerous, she is just wondering if we know what it is. The pictures are below.

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This pictures are not clear, but the description is. Our reader has found the larvae case-bearing clothes moth, or Tinea pellionella. These larvae build cases to protect their soft bodies as they move around. The cases are made of silk and other readily-available materials. As a result, they can vary in appearance significantly. Two examples are below.

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Larva of Tinea pellionella in its protective case. Photo by IKAl (Own work, CC BY-SA 3.0, via Wikimedia Commons)

 

Another Tinea pellionella larva in its protective case. Photo by Patrick Clement (CC BY 2.0)

 

Like many larvae, these go through several instars and get bigger with each change. Every time it changes instars, it molts and then builds itself a new, larger, case. The largest of the larva are a bit over ¼” long (~6.5mm). Its case is large enough that the larva can actually turn around inside it.

When the larva is ready to pupate, it finds a safe place to settle. Then, it makes some renovations to its case to change it to a pupa. Inside that pupa, it will mature into an adult case-bearing moth.

 

Adult Tinea pellionella. Photo by Sarefo (CC-BY-SA-2.5)

Our reader is correct, these larvae do not pose a danger to her, her children, or her pets. However, if she has any woolen clothing or rugs then she and these house guests are likely to have some conflicts. These larvae are known to be ravenous and can cause serious damage to wool. Unfortunately, they are notoriously difficult to control. This is partially because the larvae tend to stay in corners and other dark, hidden locations. Because of this regular vacuuming and dusting may not be enough.

We recommend denying these larvae access to food. This includes storing woolen clothes in airtight containers. Also, it is a good idea to not allow old spider webs to accumulate, as these are one of the larvae’s favorite foods. However, if our reader is not having any issues with these critters eating her woolens, then she can just let the larvae live their happy little lives.

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Today, we will discuss an email from a woman who has found an unusual creature in her room. She describes the creature as being less than an inch long. She also says that it has a single black line around that head, which she describes as black or dark brown. The oddest thing, she says, is that seems to be carrying some sort of shell with it. This shell appears to be hairy and looks a bit like a cocoon.
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