S6E5: Moths and Wasps – Tasty Collections and ‘Confused’ Insects

In this episode Rosa steps away from feathered objects to consider how museum collections and archives should be thought of as living ecosystems. She discusses how webbing clothes moths are understood as ‘pests’ and some of the strategies curators are trying to employ to manage them: including sexual confusion and the introduction of parasitoid wasps. 

• Pitt Rivers Museum
• Oxford University Natural History Museum
• National Trust launches pest-control trial combining wasps and moth pheromones
• The Lion’s Historian by Sandra Swart

Credits:

• Recorded: 28 May 2025
• Claudia Hirtenfelder, executive producer, editor and co-host 
• Rosa Dyer, script writer, narrator and co-host
• Rebecca Shen, episode artwork and logo
• Gordon Clarke, bed music
• Other sound effects from Bill Hayes - I Know an Old Lady (Archie Bleyer, Internet Archive)
• Learn more about the team here. 

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Transcript

Siobhan O'Sullivan 0:01

This is another I Raw podcast.

From Specimens To Living Ecology

Claudia Hirtenfelder 0:12

Welcome back to season six of the Animal Highlight, where we're focused on animals and museum collections. And in today's episode, Rosa does something which I find really delightful is she focuses on the animals you find in and amongst collections. So I've done a lot of work in archives, and it was really interesting to just think about who is being found and navigating archival spaces. And Rosa brings into view for the first time in this season two animals that are not birds. We talk about, we talk about moths and wasps and some of the relationships that are being fostered between them, being made between them in kind of collection spaces behind the scenes. I hope you enjoy. Hello, Rosa. Welcome back to the animal highlight. I have to admit, I think this might be my favorite script of your your season. I very much enjoyed reading this and I'm looking forward to hearing uh more.

Rosa Dyer 1:18

Yeah, thank you, Claudia. Yeah, I think this might also be my favourite episode because, you know, you know I love my birds, but this was actually a really different exploration for me when I was doing the research for it. So yeah, I hope I hope it'll be enjoyable to listen to.

Claudia Hirtenfelder 1:30

100%. I mean, it's also so spatial and it's so tactile. So anyway, I'm gonna keep quiet. You, you, you talk.

Moths Enter The Frame

What Webbing Clothes Moths Eat

Rosa Dyer 1:37

Well, so so far when we've been looking at museum collections, you know, I focused on usually individual species or even you know individual specimens, and that's kind of been the focus. But when we were talking about the dodo last week, we kind of encountered this thing of degradation and the fact that these objects aren't stable because the museum environment itself is often a place where you know weird biological processes are happening that means decay of object occurs. So, in the case of the dodo, it meant that only a head and a foot was there. Um, and so kind of despite our best efforts, objects, particularly those that are made from organic materials, so the animal objects we've been talking about, they're often really susceptible to processes of decay. And so this kind of really got me thinking about what might cause animal objects to change in the museum. Um, and it kind of led me to this really fascinating world of webbing clothes moths and then parasitoid wasps. So let's get into that. So the focus of my PhD isn't really on the conservation objects, so I'll be the first to admit that this is not my area of expertise. So I hope I'm not going to get anything massively wrong here. But one of the things I have come across, um, so I mostly work on feathers, and I often get told, you know, be careful touching the feathers because they've often had um anti-p uh anti-pest control treatment put on them, so often nasty chemicals to stop things from eating the feathers. And so what I wanted to kind of get into is well, who is eating the feathers? Who are these beasties? That are these, you know, we use kind of the quite nasty word of pests to describe them, but what are the strange ecological interactions that are happening in a museum that mean things are being nibbled by these pests? So the first kind of animal highlight creature I'd like to introduce to you is the webbing clothes moth. I don't know if you know much about them. I kind of personally have a slightly annoying interaction with them in that they eat my wool jumpers in my house because I live in quite an old cottage and it's just infested with these things. So every winter I bring out my jumpers and they've just got these little holes in them, which does annoy me.

Why Museums Are Perfect For Moths

Claudia Hirtenfelder 3:30

Yeah, I've got I've always got these little holes. I've I've been trying to figure it out, but it's always near my like the stomach area. And for a long time I thought it was moths, but I think we've recently figured out that it's actually friction from belt buckles. This is what we've I think, I think, I don't know. Um, I mean it could be moths, it could be buckles, but it's something's happening. Um, but yeah, I love this uh this focus on degradation in the archive because it is such a it's a weird place of things maintaining and sustaining, but also degrading at the same time. Um so there's this like preservation happening, but also this acceptance and refusal that things are going to decay. Um anyway, tell me more about these moths.

Rosa Dyer 4:11

Yeah, completely. And I also think like for me as someone working in museums, it also kind of really puts into question this idea that museums are safe spaces or spaces where objects can be protected, because that's one of our kind of main arguments for having a museum. But actually, as we'll see, they're infested with moths oftentimes, which eat things. So the moth we're going to talk about is the Webb and Claire's moth. I'm not going to try and pronounce its Latin name, it'll be on the blog post. But I think as we've previously talked about, I'm not great at pronouncing them. But they're these really tiny little unassuming insects. So they're about five cents five millimeters long. They're kind of pale greyish in colour. And they're probably not, you know, if you're asking a child to draw a moth or a butterfly, which is obviously similar, you probably wouldn't necessarily go to web enclosed moths. You know, they're grey, they're tiny, they're not really eye-catching members of the family. But they're probably one of the moth species that we as humans have the most contact with. As I said, if you're like me and you're like united jumpers, they're probably kind of these invisible things that you're having an ongoing, you know, fight with about who owns your jumper because they do like to eat them. Despite this kind of history, I've come to really appreciate them through reading about them and researching for this episode because they're just like the fact that they are so destructive is really amazing. So it isn't actually the adults, you know, the kind of winged form of the closed moss that caused the problem for our jumpers or our museum collections. So the adult moths themselves don't actually eat at all. They don't even have mouths, I don't think. Um it's insane, isn't it? So they only live for a few days or weeks in their adult form, but in their larval form. Well, you just blew my mind.

Claudia Hirtenfelder 5:41

There's an animal that doesn't have a mouth.

Rosa Dyer 5:43

No, so I guess, and I think it happens with quite a lot of insects, is that because their adult form is their kind of only job is to reproduce, they like just get that over with and they don't really want distractions from other things, you know, like the pesky annoyance of eating, so they don't need a mouth.

Claudia Hirtenfelder 5:58

Okay, okay. My mind is officially blown. It's mad, isn't it?

Rosa Dyer 6:03

And so in their larval form, which is, you know, prior to them being in their adult winged state, is where they do all of their kind of annoying munching. So they're amazing as well as animals, which I think is quite rare in that they can eat keratin. So they eat keratinous materials, so things like um anything sort of animal-based, so your hairs, your um wool, uh anything that's kind of natural, like naturally animal-based, and things like oils as well, they'll be very attracted to. Um, so the fact they can eat keratin is just really amazing because it's really hard to digest, you know, if you think of eating hair or nails, that's kind of, you know, the last thing you'd probably eat on something. Um but the fact that they can do this is because we think, at least it's you know, an ongoing theory, I think, that they have these um particular digestive enzymes which can process keratin and actually mean that they can convert what they eat um into water. So they can produce their own water, which means they can thrive in really dry environments as well, which obviously makes them really great candidates for museums where you know humidity is often controlled in order to try and stop these processes of decay. So they're really kind of these amazing adversaries for museum collections, because they, you know, thrive in the very environments that we're trying to control, basically. And this proclivity for kind of keratin-based materials and this tolerance for low humidity means that, you know, they're very difficult to control in museum collections. They're one of the most common museum pests, which is you know, often a word we throw around and I think, you know, is very anthropocentric in how we're thinking about these insects. But you know, if you talk to any museum curator or conservationist, you'll hear the word pest when heard about them. And they'll discriminately eat anything keratin-based. So things like textiles, woollen items, um, also things like fur and feathers. So, you know, the feathers I research are one of the kind of most obvious candidates for being munched. And they'll also happily munch on things that aren't keratin-based but do have animal products on them. So if you have, for example, uh a cotton shirt in a collection but has got food matter on it, they'll be attracted to that or animal oils and things. And so, particularly cases like um the museum I work with, the Pit Rivers, which have very dense collections and very dense displays, they're really susceptible to being munched because there's just so much there for the creatures to move from one to the other, you know, within a single case.

Claudia Hirtenfelder 8:15

And is it a matter of once the moths are in that environment, they're quite difficult to control, or is it just a matter of they're always in these environments and it's I think, yeah.

How Moths Spread And Thrive With Us

Rosa Dyer 8:25

I mean, what's interesting is that they don't seem to have been a problem for European museums or, you know, in our homes for actually that long. It only seems to be really from the 19th century in Europe. So the numbers do seem to be on the rise and they are are found in human dwellings all over the world now. They're classed as this interesting word called a synanthropic species. So, you know, one of the organisms that really thrive by living in human-made environments. So they tend to be more common, for example, in urban environments where there's a lot of warm houses that they can live in. And unlike other kind of moth species, they seem to almost exclusively thrive in urban environments. So we tend to think of cities as places that aren't great for animals or other species other than humans, but actually, this is one of the species that does really like those places. They don't seem to survive that well in really cold winter conditions and they don't seem to take up residence in places that other moth species might do, like birds' nests, for example, where there's organic matter. So they really do seem quite married to us as people.

Claudia Hirtenfelder 9:18

And again, why why museums and archives would be because they are such controlled environments in winter, summer, the temperature is controlled, the humidity is controlled. So it just makes it this really stable environment that once you've established yourself, you're you're you're set, right?

Safer Strategies Replace Toxic Pesticides

Pheromones And The Art Of Confusion

Rosa Dyer 9:32

Totally. Also, the way that they probably traveled into Europe, I think, is probably very married to people. So we're not really sure how they got there, but certainly we see kind of, you know, in the archive of understanding how moths got here, um, they're mentioned kind of from the 19th century. Or we think it's quite likely that they came from Africa and travelled over on things like trophy heads, so people killing large game animals and bringing the heads over from Africa to Europe, they could have travelled there. Um, there's one record of a naturalist on the HMS Challenger in 1823 who um spends quite a lot of time in his account of the kind of you know bigness of the voyage, being quite annoyed that all of his garments are being eaten by moths, which I found quite funny when I was reading. So, yeah, we know that they're here and they haven't been here for that long. But yeah, as you say, they are really thriving and their populations do seem to be going up. So they're an increasing problem for museums. We're not really sure why they're increasing, that's the other thing. So the changing climate conditions in museums might be one reason. So whereas previously I think people were expected to kind of suck it up and be cold in a museum, and you know, they were really kind of drafty big spaces. Now, you know, we try to make them more habitable for people visiting, so they're slightly warmer, so they're probably slightly nicer for the for the moths to live in. And also, I think the the big thing is that as a profession and as a kind of practice, museums have changed in how they manage pests and pesticide use. So previously there would be really, really harsh chemicals used on a lot of these objects. So things like mercury or arsenic would have been used, and obviously we've now tried to move away from that. So there's now been some kind of much more creative ways in which in which the moths uh as a population control thing um are being kind of yeah, managed, which I found kind of the second thing I found really interesting about this, not just you know, the amazing things like them not having mouths, all that how prevalent they are, but actually how the kind of new strategies that are coming in to control them. Because um it has been a re like kind of the way it's been present in my life as a researcher is that when I handle featherworks, for example, which is my main thing, um, I have to wear gloves and even sometimes a mask because these older collections say things like from the 1890s, for example, which is a lot of the collections I work with, are covered in awful stuff like mercury or arsenic. And it's a really, you know, a proper concern for people that are constantly in contact with these objects. And also makes the objects hard to interact with, particularly when you're, for example, working with indigenous communities who made the objects in the first place, you then want to have a relationship with them. Actually, their existence in the museum has made them harmful for that relationship to take place. So most museums today acknowledge that the complete eradication of what we call pest species is not really a realistic goal. Um, and instead, most do what is the sexy term of integrated pest management systems. So this is based on measures that reduce the kind of desirability of the environment for species, which might damage collections, and also try to limit the opportunities for those animals to feed and breed. So you're making it a place where they don't want to live, and if they're living there, you're making it more difficult for them to continue living and thriving there, basically. And the kind of two methods that I came across whilst reading for this ranged from like romantic comedy to kind of a really kind of like alien horror show. So I thought I'd just mention two of them, which I just found brilliant. So the first strategy is a pest confusion strategy. So one way that they limit these moths from breeding, and it sounds really made up, and it's a it's a non-toxic treatment, so it's not, you know, directly harmful to the moths in any way, is they use something to try and confuse the moths when they're seeking out breeding partners called exosex. And this is used basically by luring the male moths into a trap using female moth pheromones. And then as they leave the trap, the moths are covered in the pheromone themselves. So they go flying around. And what it does is a for the moth that's been covered in the pheromone, they're so stinky themselves that they can't smell other females anymore. And also because they smell of a female, they then attract all the male moths to them. So you end up with just these congregations of male moths not really knowing what to do with themselves, and all of the viable females don't have any males, so you know the whole breeding cycle breaks down. Um, and because the adult moths only live for a few weeks, the hope is that in doing this, you basically break up the breeding cycle, and over time the moth population will reduce without any need for using toxic pesticides or even directly killing the moths. You're just stopping them from maybe able to find each other properly, which I thought was like absolutely ridiculous, but was it kind of amazing?

Claudia Hirtenfelder 13:56

Are there any ramifications, do you know, of like a decline in these moth populations? Like, would it impact other species in any way?

Rosa Dyer 14:03

I don't know. I think like, yeah, that would be I don't know if anyone studied that of if it also affects other insects and stuff that are in the museums, because obviously moths aren't the only thing living there. Um I do think though that there's quite good evidence that this works and that it does reduce moth populations. Um I think this is a slightly older strategy than the second one I'm going to talk about, which is kind of really cutting edge and I think has only just recently been introduced. But yeah, no, that's a good question. I don't know if it has if these kind of pheromone markers have have any concerns for other other species that would be present.

Claudia Hirtenfelder 14:36

Okay, what's the uh second strategy then?

Ethics, Risks, And Ecosystem Lessons

Rosa Dyer 14:39

So the second one, so if the pest confusion treatment was our romantic comedy, this one is kind of the monster versus alien side of things. So museums have been experimenting using a different form of biological pest control by maybe quite counterintuitively introducing more insects into the museum through the use of these things called parasitoid wasps. Um I don't know if you knew much about them. This was also just a completely new thing to me when I was reading about it. And to be honest, like further down the line, they should just have their own animal highlights episode because they just like they're fascinating. So I mean wasps are incredible, yeah. They're so cool. So nearly all orders of insect and arachneg and arachnid in the world will have a corresponding species of parasitoid wasps. So there's hundreds and hundreds of species of them. And so the eggs and the larvoy of the Lepidopter ephemery, so the moths and butterflies, seem to be particularly susceptible to them. So basically, what they do is they're super important for us as humans firstly, because they help us to damage insect populations. So what they do is they work by depositing their eggs into other insects. So this will vary between wasp species. Um, some will deposit eggs into the larvae or adult stages of insects, and others, like the wasps, which target the webbing clothes moths, will deposit their eggs into the eggs of moths. So you have a moth egg, and then your little parasitoid wasp comes in and lays its own egg within that egg. And then what this does is that instead of the moth hatching, the wasp larvae will hatch and then emerge and eat the moth egg as a source of food, and then it will develop into an adult wasp before hopefully breeding and continuing on its cycle. So, what the wasp does as well in a similar way to the exos eggs is it's disrupting the kind of breeding cycle of the moths in the museum. The thing I also found just amazing about this, I don't know if I said before, is that this is all happening on like at absolutely microscopic levels. So these aren't the kind of wasps we see in our garden who might be on our jam and our picnic, they're tiny. So the wasp lays a 0.5 milliliter millimeter egg into the moth eggs, which are only 0.3 millimeters in length. So it's like absolutely tiny. And they're complete, so therefore, you know, as a as a visitor walking around the museum, this is completely unnoticeable. It's not as if you're seeing, you know, moths and wasps flying around and disrupting your ability to see the objects. It's happening at a completely microscopic level. Um, and the technique of kind of purposely introducing parasitic wasps is something that's I think really growing in usage in the heritage sector. And big organizations like, for example, in the UK, the National Trust, has really been implementing them as part of their integrated pest management strategies recently. So it's quite a new thing, but I think is something that's definitely seen to be successful and is really taking off the way to manage more populations because we know they're on the rise and we know that they're harmful to collections, but doing it in a way that doesn't introduce further harmful chemicals into the kind of whole museum space, which yeah, I just found it absolutely just mind-blowing, as you say, to think about this.

Claudia Hirtenfelder 17:29

Yeah, it's interesting because I feel like that's actually a relatively, I mean, you say it's new in the collection space, but I think this idea of using animals to control other animals is a relatively old strategy, and it hasn't always had um the effects one would hope for, right? So a classic example here are the cane toads in Australia, New Zealand. Um Australia, I'm gonna go with Australia, uh the cane toads, um, because they were introduced to try and control a grub that came on colonial ships, and then the cane toads went out of control, and now they're trying to introduce other animals to take care of the cane toads, which is not proving to be as successful. And I read um just the other day, I'm busy reading The Lion's Historian, which is a cool book about kind of the history of animals uh on the African continent. And one is about an island just off of uh South Africa, and again, there was an introduction of an insect, and then they tried to introduce a parasite, and then they tried to introduce cats, and then they had to do it. So it was just a series of like re-introductions of different, and I'm getting, I'm probably getting all of this um muddled up with regards to who was introduced when, but it was just fascinating how the trying to use some animals to control other animals doesn't always end up uh the way people initially think it's going to. Sometimes the animal that you introduce to control the other animals becomes an even bigger problem. Uh, is there any kind of threat or concern about that with regards to the wasps? None of that I have come across.

Think Like A “Pest” To Preserve

Rosa Dyer 18:59

As I said, I think this is still quite a fairly new thing. Like the papers I were reading with, you know, a lot of them were from the 2020s, even. So there's still, I think it's a new thing that's coming in, and it's maybe a bit too early to to assess that. But yeah, it's obviously yeah, one of those concerns that you want to keep in mind. I always think of that um the nursery rhyme. There was an old lady that swallowed a fly, and then she, you know, progressively eats-there was an old lady who swallowed a fly.

Claudia Hirtenfelder 19:24

Yeah, yeah. I don't know why she swallowed a fly. Perhaps perhaps she'll be a fly.

Rosa Dyer 19:28

And then she eats then she eats a spider and the spider eats a cat and the cat eats a dog, like all the other way around it, like yeah, it gets bigger and bigger.

Claudia Hirtenfelder 19:36

Oh my god, I haven't thought of that song in a long, long time.

Bill Hayes 19:41

Uh no lady who swallowed a fly. I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a spider that wriggled and jiggled and tickled inside her. She swallowed the spider to catch the fly, but I don't know why she swallowed the fly, perhaps she'll die.

Claudia Hirtenfelder 20:03

Um, well, that was awesome. Um, as someone who spends a lot of time in the archives and also thinking about the ways in which um how I can find animal stories in the archives, and I think it's similar for you with museum collections, trying to find animal stories in this historical artifact. Um, I don't think I'd ever spend time trying to think about the live animals in these spaces, right? That they are multi-species spaces in and of themselves, which I just think is um a really nice take on thinking about museum and archival collections.

Rosa Dyer 20:32

Yeah, it's brilliant, isn't it? And I I just I really love the idea as a museum visitor that as you're kind of walking around looking at these other objects, you might be in the presence of this, you know, really weird and complex world of like sexual confusion and parasitism that is just happening on this microscopic level. Um yeah, I also remember one conservator when I was, you know, vaguely thinking about this to do with feathers, and uh came up to me once and we were talking, you know, about insect populations as you do in a museum. And he said, you've got to learn to think like a pest if you're going to be a museum conservative conservator. And of course, like pest is a problematic word, I think. But I really like this idea that, you know, you need to get into the mind of the animal and think about, you know, really in detail about their lives, about their breeding strategies and about their kind of life histories as a kind of almost animal-centered alternative to just, you know, killing them quite indiscriminately with arsenic or mercury, which has really detrimental effects for hundreds of years to come. Instead, you know, you think like them off, and that helps you to manage it in a much more hopefully sustainable way.

Claudia Hirtenfelder 21:34

Really interesting. Well, thank you so much, Rosa, for uh another wonderful uh highlight.

Bill Hayes 21:42

I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a horse, she's dead, of course.

Claudia Hirtenfelder 21:55

Thank you to Rosa Dyer for co hosting this animal highlight with me, and to Rebecca Shen for doing the Animal Highlight logo and all of the episode artwork. Thank you to Gordon Clark for doing the bed music. You would have heard another song in this episode that was by Bill Hayes I Know an Old Lady. I bet it's still stuck in your head. This episode was produced by myself.

Siobhan O'Sullivan 22:18

This is The Animal Highlight with me, Toria Hirtenfelder.com. That's I R O A R P O D.com.