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Jumping spider mimicry in Brenthia moths

Many insects deploy mimicry to fool their predators into thinking they are highly defensive, venomous, or simply not to be messed with. A great fraction of mimicry cases involve adopting the appearance of ants, wasps, and spiders for these exact reasons. One of the most interesting cases, however, is predator mimicry: insects that take the appearance of their potential predators in order to expose them. I have already written about one such case in crambid moths, but in this post I want to present one of the classic examples for this mimicry in metalmark moths of the genus Brenthia.

At first glance, metalmark moths do not really resemble spiders. In my post about Petrophila moths I mentioned that observed spider mimicry might also be a case of pareidolia. In other words, we as humans seek familiar patterns surrounding us, so we recognize the image of a spider on the wings, but is it really mimicry? And indeed, after posting I was accused of having a strong imagination for thinking this is mimicry. There is a good point being made here – in the case of Petrophila there is a temporal barrier preventing the two from encountering each other under normal conditions. Petrophila moths are nocturnal while jumping spiders are diurnal. Nevertheless, the prevalence of such wing patterns in the insect world suggests that they have a role in the survival of those organisms.

Metalmark moth (Brenthia hexaselena) displaying its typical body posture, with wings raised like a peacock's tail.

Metalmark moth (Brenthia hexaselena) displaying its typical body posture, with wings raised like a peacock’s tail.

Brenthia moths are no different. It takes some imagination to strip them of their mothy characteristics to see the resemblance to jumping spiders. Members of family Choreutidae, the genus contains over 80 described species, all sharing the same appearance: a unique body posture, and wings patterns that are reminiscent of jumping spiders’ eyes. In fact their common name, metalmark moths, is due to the convincing “catchlight” area of the eyespots, often consisting of silvery scales. Brenthia species also move like jumping spiders, advancing by short bursts of movements while still retaining their wing display. Lastly, these moths are diurnal and can be seen active on top of leaves, just like salticid spiders. If you think it ends there for these moths in regards to anti-predator defenses, let me also add that their caterpillars deploy defense strategies as well. When alarmed, they launch themselves through holes chewed into the floor of their webbed feeding shelter, giving the term “teleporting through a wormhole” a new meaning.

Metalmark moth (Brenthia hexaselena) in frontal view, displaying wing patterns that resemble a jumping spider's face and legs.

Metalmark moth (Brenthia hexaselena) in frontal view, displaying wing patterns that resemble a jumping spider’s face and legs.

Brenthia moth (upper image) mimics jumping spiders (lower image) with wing markings, wing positioning, and posture. Figure from Rota and Wagner 2006 (drawing by Virginia Wagner).

Brenthia moth (upper image) mimics jumping spiders (lower image) with wing markings, wing positioning, and posture. Figure from Rota and Wagner 2006 (drawing by Virginia Wagner).

Portrait of a jumping spider (Phiale formosa). It is a little difficult to see the resemblance to the moth's wing patterns, but the important thing is that it works to the moth's benefit.

Portrait of a jumping spider (Phiale formosa). It is a little difficult to see the resemblance to the moth’s wing patterns, but the important thing is that it works to the moth’s benefit.

When discussing animals mimicking their predator, it is important to remember that we humans are not the target audience. This means that the imitator may not look too convincing in its mimicry to us, but still manages to trigger a desired response from said predator. However, when in doubt, the best way to know for sure is to put the suggested mimicry to the test through a series of experiments. Brenthia moths have become one of the best examples of spider-mimicking moths, thanks to rigorous testing. In their classic paper, Rota and Wagner placed the moths with their potential predators, jumping spiders of the species Phiale formosa, in arenas and recorded the outcome. They also used non-mimicking moths of the same size as control for the experiments. The results showed that the jumping spiders respond to Brenthia by displaying territorial behavior and waving their forelegs. In other words, upon noticing the Brenthia moths the spider predators immediately expose themselves. It comes as no surprise that Brenthia moths had a high survival rate in the experiments, as they could take off once the danger was revealed, avoiding predation. The control moths did not trigger a territorial response from the spiders and were preyed upon extensively.

Jumping spider (Phiale formosa) displaying territorial behavior in response to its own image. This is when the moth knows it is in danger.

Jumping spider (Phiale formosa) displaying territorial behavior in response to its own image. This is when the moth knows it is in danger.

One thing to keep in mind though is that this mimicry works well only because salticids are special among spiders. They do not make a web to capture prey, but instead rely on their excellent vision to detect prey. They are active predators, and therefore display a wide array of behaviors to communicate with other salticids. Jumping spiders will avoid other jumping spiders due to the risk of cannibalism. Brenthia moths take advantage of this behavior to get the higher ground by delaying the spider’s attack in order to escape. This makes them one of nature’s greatest con artists, but when survival is on the line, anything is kosher.

Papers mentioned in this post:

  • Rota, J, Wagner DL (2008) Wormholes, sensory nets and hypertrophied tactile setae: the extraordinary defence strategies of Brenthia caterpillars. Animal Behaviour 76(5): 1709-1713
  • Rota J, Wagner DL (2006) Predator Mimicry: Metalmark Moths Mimic Their Jumping Spider Predators. PLoS ONE 1(1): e45. https://doi.org/10.1371/journal.pone.0000045

This leaf got me thinking

I sometimes like to drift away in my thoughts and reflect on my days before becoming a biologist. It is amazing to realize how much I have learned over the years. This is something I think many people take for granted nowadays. We are flooded with easily accessible information on a daily basis. Try to think how many new things you learned just in the last month.
A little over a decade ago, I embarked on my first big overseas trip. Back then I knew close to nothing about Latin America. I had one goal in mind: to see poison dart frogs in the wild. Not too long into the trip I already felt victorious, after spotting some of these frogs in Bolivia and Ecuador. My quest took me to Costa Rica, where I found more of these stunning hopping jewels. Although I was mainly interested in amphibians, I was overwhelmed by the richness and diversity of arthropods. And more interestingly, despite my knowledge and exposure to various insect species, I realized how much I do not know and need to learn.

One such moment occurred when I visited the pastoral town of Monteverde, more specifically the butterfly gardens there. The guided tour I took passed near a moth wall, which was basically a white painted wall with a powerful light source pointing at it during nighttime. This was the first time I have ever seen a light trap. It was packed with hundreds of moth species. I was fascinated. The other visitors – not so much. They were pressing me to leave these “boring brown bugs” so we can head over to the butterflies area. “Just a second” I replied, “there is one moth I have to photograph”.

Leaf-mimicking moth, Monteverde, Costa Rica

Leaf-mimicking moth, from Monteverde, Costa Rica. Amazing camouflage, down to the level of leaf (=wing) damage and asymmetry. Image scanned from an old film slide.

“That’s not a moth” argued one of the visitors, “it’s just a fallen leaf that was blown onto the screen door”.
The local tour guide smiled but kept his silence.
“Well, if it is just a leaf…” I said and stood up, “…why don’t you touch it then?”
Upon being touched, the “leaf” immediately came into life and took off in a slow flight, disappearing into the foliage.

Many insects try to look like leaves. It is one of the most common types of crypsis. Only some of these insects, however, take it to the next level, mimicking not only the shape and color of leaves, but also their texture, tissue damage and even asymmetry. This moth had all of these. For years I have been waiting for an opportunity to photograph such a moth again, and finally, last year, I stumbled upon a similarly impressive species in the Amazon basin of Ecuador.

Leaf-mimicking saturniid moth (Homoeopteryx sumacensis), Amazon Basin, Ecuador

Leaf-mimicking saturniid moth (Homoeopteryx sumacensis) from the Amazon Basin, Ecuador. It was resting on the bathroom floor – I do not think I would be able to see it if it was resting among fallen leaves.

This species does look (and behave) very much like a leaf. Instead of laying flat like most moths, it holds its wings up in a way that creates a three-dimensional appearance. The forewing tips and margins are delicate; they are usually the first part to suffer tears and damage, contributing to the asymmetrical look of the false leaf. I knew immediately that I want to keep this photo for something special, and I decided to share it on the last day of National Moth Week. After posting it, the internet went wild. The photo was shared hundreds of times on social media, sparking discussions about evolution and moth diversity. It encouraged people to post their own photos of cryptic moths; others messaged me that the photo helped them to see the beauty and uniqueness of moths. I could not be happier.

Leaf-mimicking saturniid moth (Homoeopteryx sumacensis), Amazon Basin, Ecuador

From this angle it is easier to see that it is a moth. Leaf-mimicking saturniid moth (Homoeopteryx sumacensis)

It is important to remember though, that this moth is just one small example from a vast world of moths. There are over 150,000 species of moths worldwide, many undescribed, and many more waiting to be discovered. Moths are everywhere. There is more to them than meets the eye. They take many forms, and can sometimes make you doubt yourself. Until that moment in Costa Rica I was not aware these leaf moths existed, and even today I am not certain of their exact species ID*. Even nowadays within the highway of free information, I still have a lot to learn.

The positive feedback this photo received, as well as my orchid bees photo, made me realize also how much I am grateful for all the people who find my content interesting or inspiring. I never mention this, but it gives me a lot of energy. When things get rough, I remind myself that there is at least someone out there who thinks what I do is cool. I want to take this opportunity to thank all my followers, commenters and visitors. I got to know some fascinating people since I started posting. Thank you, everyone.

*UPDATE: This moth has been identified by Vazrick Nazari from the Canadian National Collections as Homoeopteryx sumacensis, a saturniid moth.

(Inter-)National Moth Week

When all that people talk about right now is going outdoors with their smartphones and tablets to play the current-trendy Pokémon Go, an augmented reality game of hunting fictional creatures, it seems appropriate to remind everyone that a similar “game” was already in existence centuries ago and still goes on today. It is called being a naturalist, and the rules are pretty simple – you just go out to search for, observe, and document everything that nature has to offer. I guess making people spend more time outside is a good thing nowadays, I just wish they were looking more around them instead of having their faces glued to mobile screens. Nevertheless, many players reported that while playing the game they stumbled upon “real life Pokémon”, in other words wild animals such as snakes, birds and even mammals. Several biologists on twitter decided to take a nice turn on this game and came up with the hashtags #PokeBlitz and #PokemonIRL, tagging and spreading facts about various wild animals, plants and fungi. It is a cool initiative that I hope will spread like fire, but in any case I wanted to use this opportunity to mention another similar event happening this month – National Moth Week.

Geometer moth (Rhodochlora brunneipalpis), Limón Province, Costa Rica

Green geometer moth (Rhodochlora brunneipalpis) from Limón Province, Costa Rica

National Moth Week is a citizen science project that sets out to increase public awareness and appreciation of moth biodiversity. It has been running continuously for 5 years, with the main event taking place on the full last week of July. During this week, moth enthusiasts set up light traps to attract moths and record the species found in their area. They are often joined by professional lepidopterists (scientists studying this insect order), who offer assistance in identifying moth species and wait for cool and unexpected discoveries. With the current accumulating evidence of dwindling insect populations, especially those of pollinators like Lepidoptera and Hymenoptera, this activity has huge importance. National Moth Week has become a global joint effort to record moth species, yet the project’s title remains “national” to emphasize the outreach activity on the local scale. Anyone can join and attract moths in the comfort of their own home, but many groups hold moth-watching events at public locations, attracting a large crowd of enthusiasts and curious people (you can attend an event close to you by searching in the event map).

Crambid moth (Desmia bajulalis), Mindo, Ecuador

Many Crambid moth species, like this Desmia bajulalis from Ecuador, have iridescent scales on their wings.

Setting up a light trap for moth watching is super easy. All you really need is a light source, and turning on the porch lights is probably the simplest way to attract moths. If you want to invest a little more, you can get a light bulb with some output in the UV range, as many moth species are attracted to this type of light. Many entomologists and insect enthusiasts use high-output mercury vapor bulbs because their spectral range seems to be more attractive for insects compared to other bulbs. Personally, I do not like these bulbs; they are very fragile, become extremely hot during operation and quite finicky to set up in remote locations. I use a compact version of a bulb that has a similar spectral distribution and get good results. My setup is built to be portable, so I now take my light trap almost anywhere I travel.

White witch moth (Thysania agrippina). Amazon Basin, Ecuador

Sometimes a light trap is not even needed for attracting moths. This gigantic white witch moth (Thysania agrippina) came to our bathroom lights in the Amazon rainforest, Ecuador.

light-trap

The light trap I used at Caves Branch, Belize, attracted a nice variety of interesting moths, including members of genus Petrophila (mentioned previously on this blog).

Moths attracted to light trap, Mindo, Ecuador

Moths (and other insects) gathering around a light trap in Ecuador

Moth feeding on top of another moth's wing, Mindo, Ecuador

When it gets crowded at the trap interesting behaviors can be observed, like this small moth feeding on a bigger moth’s hemolymph.

Finally, if you want to be able to record the species coming to your trap, you will need a surface for them to rest on. The simplest way to do this is by stretching a white sheet behind the light source. The flying moths will come to the trap, bump into the sheet and cling onto it, allowing close observation and photography. Not only moths, but also other arthropods can end up coming to the light trap as well. And, if you are lucky, even amphibians and reptiles can show up to take advantage of the abundant food.
The best thing about setting up light trap is that you never know what will show up. It is not uncommon to encounter a species that you do not know, or even better, find something that is very rare.

Geometer moth (Eutomopepla rogenhoferi), Mindo, Ecuador

Geometer moth (Eutomopepla rogenhoferi) from Mindo, Ecuador

Giant silk moth (Rhescyntis hippodamia). Amazon Basin, Ecuador

Giant silk moth (Rhescyntis hippodamia), one of the heaviest and largest moth species found in the Amazon Basin of Ecuador.

Geometer moth (Opisthoxia uncinata), Limón Province, Costa Rica

Geometer moth (Opisthoxia uncinata), from Limón Province, Costa Rica. This is probably one of the most common species in Latin America, it showed up in every light trap I have set up so far.

Wasp-mimicking moth (Gymnelia sp.), Mindo, Ecuador

Do not forget to check the surroundings of the light trap for even more species! This wasp-mimicking moth (<Gymnelia sp.) from Ecuador was found resting on the wall a few meters from the trap.

White geometer moth, Limón Province, Costa Rica

Some moths remind me of common butterflies. For example, this moth from Costa Rica somewhat looks like Small White (Pieris rapae)…

Giant silk moth (Titaea tamerlan). Amazon Basin, Ecuador

Giant silk moth (Titaea tamerlan) from the Amazon rainforest of Ecuador

Green moth (Epidelia sp.), Caves Branch, Cayo District, Belize

Green moth (Epidelia sp.) from Belize

Crambid moth silhouette, Mindo, Ecuador

Even a silhouette can be interesting! Crambid moth from Mindo, Ecuador.

Owlet moth (Sosxestra grata). Caves Branch, Cayo District, Belize

Sosxestra grata has become one of the most iconic Latin American owlet moth species, thanks to an excellent photograph taken by Thomas Shahan in BugShot Belize.

Crambid moth, Mindo, Ecuador

Some of the nicest wing patterns are found on the smallest species, like this delicate Crambid moth from Mindo, Ecuador.

So go out, and enjoy this fun activity. Moth-watching is the new birding. In fact, it might even be better than birding. It requires much less effort and preparations. In addition, the diversity of moth species found in a limited area can be astounding compared to that of birds. There is so much out there to discover, you really just have to look.

Petrophila: Salticid-mimic moths

A few months ago, I returned to Belize to conduct a small arachnid survey. While I was there, I took part in designing insect light traps for Caves Branch Jungle Lodge. The concept of a light trap is simple – flying nocturnal insects use the moonlight to navigate at night, and when there is a brighter light source present (like a light bulb) they are attracted to it. We wanted to have a few traps set up before the beginning of BugShot, and we ran a few trials in several locations using different lighting settings to see what works best and which insects show up at the traps. Very soon we realized that the traps attracted an impressive diversity of insects, but also their predators – spiders, frogs and bats quickly learned the locations of the traps and came regularly to feed. In several occasions fire ants showed up to raid the unsuspecting insects.

Petrophila sp. in typical resting posture, partially exposing the hindwings

Petrophila sp. in typical resting posture, partially exposing the hindwings

 

One of the insects that we saw in great numbers every night was a small, plain-looking moth from the family Crambidae. I would probably not pay attention to it if it were not for four black dots arranged in a row on the margin of each of its hindwings. Many moths rest with their hindwings concealed by the forewings, however these moths, belonging to genus Petrophila, had a unique body posture at rest, exposing only the dotted part of their hindwings. This pattern looked very familiar to me, but I could not pinpoint from where exactly. Then a few nights later one of these moths decided to rest pointing sideways with its head rather than upwards like most moths. And it finally hit me: this moth has an image of a jumping spider on its wings looking straight at you. The mimicry is so convincing that the moth wings even have hair-like scales where supposedly the spider’s head is.

Side view of Petrophila sp.

Side view of Petrophila sp.

 

I should be careful here. Pareidolia is a known phenomenon in which one searches for known patterns just about anywhere. It is what makes people see the face of Jesus Christ on a burnt piece of toast, it is what makes you see a face on a rocky terrain on Mars, and it what makes you see a number when looking at the wings of Diaethria species.
What I mean to say is that the color pattern on the wings of Petrophila species reminds me of a salticid spider, and perhaps it works the same for other animals as well. There is also a behavioral display that makes the mimicry even more deceiving: the moth moves its wings to mimic the movements of a jumping spider. In search for a second opinion, I turned to someone who breathes and sleeps jumping spiders. Thomas Shahan, who fortunately was around for BugShot, confirmed my suspicion and even came up with an ID for a possible model spider: a female Thiodina sp. And so we went on to find a jumping spider that looked like the one shown on the moths’ wings. In any case, to my untrained eyes it seems that this pattern is common in several moth genera, and in other insects as well. Some will debate whether this apparent image actually evolved to depict what we want it to be, but I can only imagine the reaction of a jumping spider to this image and behavior by the moth. Jumping spiders are known to have good vision; a jumping spider will stall to examine an opponent to avoid conflict. This may give the moth a few seconds to escape. A good analysis of similar mimicry in other species is discussed here.

A different species of Petrophila, recorded from the same light trap. This one is smaller and seems to have a slightly different spider image.

A different species of Petrophila, recorded from the same light trap. This one is smaller and seems to have a slightly different spider image.

 

The same Petrophila species as above, here with a possible salticid model - female Thiodina sp. from the same location in Belize. What I find amazing is that the wings even show some of the iridescence seen in the spider's eyes.

The same Petrophila species as above, here with a possible salticid model – female Thiodina sp. from the same location in Belize. What I find amazing is that the wings even show some of the iridescence seen in the spider’s eyes.

 

Petrophila moths are unique among Lepidoptera for having aquatic caterpillars. They occupy running freshwater habitats, rivers and streams, where they feed on algae by scraping the surface of submerged rocks and stones. The genus has a wide distribution across the Americas and many species occur in temperate zones in addition to tropical regions.

You know the moths are successful in their mimicry when you find others deploying the same strategy: Nectopsyche is a genus of caddisflies (order Trichoptera) that shows a similar pattern – moth-like adults have four tiny black spots arranged in a row at the margin of their forewings, along with pale stripes.

You know the moths are successful in their mimicry when you find others deploying the same strategy: Nectopsyche is a genus of caddisflies (order Trichoptera) that shows a similar pattern – moth-like adults have four tiny black spots arranged in a row at the margin of their forewings, along with pale stripes.

 

Not only moths, but also many other insects orders were represented in our trap catch. I hope that Caves Branch continues to make good use of these sturdy light traps to record the insects surrounding the lodge. There is great potential for scientific work to be done here.

Light trap in Caves Branch, Belize

Light trap in Caves Branch, Belize