Ladybugs Have a Killer Secret

JESSICA WARE (Curator, Division of Invertebrate Zoology): How lovable are ladybugs? Look at those spots! Look at that lil round pop of color! A group of ladybugs is even called a “loveliness!” They star in nursery rhymes and many of them—like a lot of us would love to do—find winter hideaways where they just sleep through cold weather. Awwwwww. But it turns out, ladybugs have some… unexpected qualities. They’re a little more sinister than you might think…. 

They can be beautiful killers—an adult may take out more than 5,000 aphids in its lifetime—usually a little over a year. And they don’t stop there: if their normal prey runs low, ladybugs can turn on other insect predators, or even on one another…  And to top it off, when ladybugs are provoked, they’ve got quite the defensive strategy—something called “reflex bleeding.” They secrete these drops of off-putting toxic blood from their leg joints. Wow. But don’t change your mind about loving ladybugs! Some of those noxious chemical compounds just might make ladybugs even more beloved by humans…

DIRECTOR: So, Jessica, I've heard some people call them ladybugs. Some people call them lady beetles. Some people call them lady birds. Are those all the same thing? 

WARE: Yeah. You can pretty much use those names interchangeably. They’re all beetles, so they’re all Coleoptera. And we tend to want to kind of move away from calling them ladybugs because they're not bugs. Peer pressure—try and call them lady bird beetles.

DIRECTOR: Tell your friends.

WARE: Tell everyone you know: they’re lady bird beetles now. They’re all beetles in the family Coccinellidae. That name comes from the Latin word for scarlet, but they’re all kinds of different colors. This drawer has just in this one genus here, a variety of color and shape.

DIRECTOR: So, all ladybugs aren’t red and black? 

WARE: Well, I think the ones that often many of us are most familiar with are ones that are kind of red and black in color. But since there’s like 6,000 different species of ladybugs worldwide, they come in lots of different colors and patterns. 

DIRECTOR: I feel like people have a really soft spot for ladybugs, even if they don't like insects. Why do you think that is?

WARE: Well, part of it, I think, is just that they're very beautiful. We tend to like beautiful things, and we tend to kind of give special attention to things that we think hold beauty. Part of it might just be that people tend to think of them as kind of good luck or as good actors, beneficial insects. For over a hundred years, farmers have been using ladybird beetles as kind of green pest management because they like to eat aphids. 

Aphids are these tiny, tiny insects that feed on plant sap. They can sometimes be problematic for farmers and gardeners not only because they chow down on crops and flowers, but because they can transmit viruses from one plant to another. So, we don’t love them. But for ladybugs, these are just juicy green insect cupcakes. Some larvae  can eat their own weight in aphids in one day. So they’re kind of like our agricultural allies.  

WARE: Dr. Sara Hermann runs a lab at Penn State’s College of Agricultural Sciences where she and her team study insect predators—like ladybugs. Tell us where we are. What are we looking at here?

SARA HERMANN (Assistant Professor of Arthropod Ecology & Trophic Interactions, Penn State University): We are in my lab here at Penn State University, where I study a lot of different things, one of which is ladybugs. And so this is our wall of ladybugs, here. We have two different species and multiple different life stages of the ladybugs that we work with in the lab.

WARE: I’m fascinated by Sara’s work because she studies a chemical concoction from ladybugs that you could think of like a perfume of fear. Perfect for a femme fatale, right?

HERMANN: I'm really excited about thinking about predator-prey interactions. And when we think about predator-prey interactions, we're usually just thinking about predation—so, how much of something is getting eaten by a predator?

But my lab focuses on the other side of the coin, so the non-consumptive effect, the other ways that predators might influence the prey organisms without actually eating them at all. And the way that they can do this is just by being present in the vicinity of a prey organism. 

The prey—here, aphids—can detect that through odor cues or the smell of the ladybug, and they use that information to change their behaviors in a way that reduces their risk of being eaten. So we're trying to understand how aphids respond to these ladybug smells and if they change in ways that are beneficial for plants that we want to eat as humans

WARE: Sara’s trying to figure out if we can improve crop protection by harnessing the power of non-consumptive effects like that natural bouquet of ladybug chemicals. The smell seems to scare off–or at least repulse–aphids. So, what do ladybugs smell like? 

HERMANN: The adults definitely have a very specific odor. it smells like chips or French fries or bell peppers or lots of different things have actually been mentioned as their odor.

WARE: That's funny. A new- a new Yankee candle scent. I’m just sensing it, right?

HERMANN: And so what we have been doing is we have collected all of the odors that these ladybugs produce, and we can test them individually or as a blend, sort of like a perfume of ladybug. And then we can take that to the field, in theory put that out there and see if we can disrupt these aphids in ways that’s beneficial for crop production.

WARE: That’s the smell of fear. The smell of fear, smell it here. So why don't we just put a bunch of ladybugs out? I mean, putting out the perfume, what's the advantage of doing that versus just putting out ladybugs?

HERMANN: Yeah, so we do release ladybugs, sometimes. We call that augmentative biocontrol. The advantage of this strategy would be that we are sort of maximizing the entire predation effect. So the ladybugs are going to be around and that's great. But if they're not around in huge numbers, at least we're getting these behavioral changes, these physiological changes in the aphid prey that are beneficial to the crop. 

WARE: After all, we might have a hard time getting ladybugs to stay put. They’ve got wings and can fly away. So, it can be tricky and expensive for farmers and gardeners to manage their release. And, when new ladybug species are introduced for pest control, sometimes they outcompete the ladybugs and other predators that are already there.

HERMANN: So I have two species here of interest, one of which is a native lady beetle, which is interesting because it is from this area And the other species that we're studying is one that was introduced in the early 1900s—Harmonia axyridis. Once it was introduced to the United States, there was some concern that it would outcompete native species. 

WARE: So, spritzing plants with ladybug scent could potentially avoid impacting local ladybug species, while producing positive outcomes in the field. 

HERMANN: What we've studied so far is that we’re seeing fewer aphids coming into a field where the ladybug smell is. We're also finding that once they're on a plant and exposed to these smells, they're having fewer offspring and their overall population abundance is reduced,.

WARE: From fields of crops to my Nana’s tulips to arboretums like this one at Penn State, Sara’s work could benefit all kinds of growers. The goal is to increase crop yield, increase food security, and decrease insecticide use.

So I remember vividly, ladybugs as a kid. Is that how you got started? You just, like, loved them as a child? Like this is it. This is my destiny. I’m going to study everything about them. The aphids that they eat, the smells that they make.

HERMANN: No, Absolutely not. As a kid, I really was not a big fan of insects, so I definitely never saw myself going into a career path where I was studying them specifically.

WARE: What did you think you wanted to do?

HERMANN: I wanted to be a singer, a musician. But what got me into entomology was a summer job as a research assistant. I fell in love with the idea of insect behavior, and I fell in love with the idea of sustainable agriculture. I realized that so much research informs policy and can make huge strides in change. And so I decided that I would continue down the path of research, hopefully to try to do some of that work that informs policy that could lead to sustainable agricultural solutions.

WARE: As an aside, I would say The Smell of Fear would be a very cool band name if you decided to stay in the music realm. I just want to give a plug for that.

Sara’s research lets us ask some big, fascinating questions about how organisms relate to one another and to their physical environment. Non-consumptive effects—like the impacts on aphids from that ladybug smell of fear—haven’t really been studied a lot in the insect world. 

HERMANN: It's hard to study it because you're looking for something that you're expecting not to be there. A lot of the time, we're thinking about risk effects, we're thinking about avoidance. So how do you measure something that's not showing up? 

WARE: So if it's so hard to study non-consumptive effects, why do you still do it? Like, why is it important to know about them?

HERMANN: Yeah. Predator-prey interactions are one of the most important subjects in thinking about ecology, generally. They drive so much evolution. And if we ignore non-consumptive effects, we’re effectively taking away a huge portion of the possibility that a predator could have an impact on its prey. Ignoring that means that our predictive power is just not very great, right? So if we want to think about populations over space and time and we're only thinking about consumption, we're leaving out a huge piece of the puzzle. There's going to be lots of different aspects of ecological interactions that we have to consider moving forward as the climate changes the way it has been, including chemistry and how chemicals allow for interactions among species.

WARE: It’s so interesting. I always thought about, you know, what are the impacts of climate changes on the organism. And we want to conserve the organism, we want to conserve species, but in a way, we want to conserve these unique chemistries, right? We want to conserve these unique molecules that evolved over I assume millions of years. As part of this co-evolutionary process.

HERMANN: Studying something that isn't well studied is both exciting and scary. It's exciting because you always have the opportunity to tell somebody something they had no idea existed. It also provides a lot of opportunities to make discoveries. So that part of it is exciting stuff.

WARE: Ladybugs have many different common names. In the UK, people often call them ladybirds. In 17th century England, ladybugs were sometimes known as lady cows. Gotta be the spots, right? In Spanish, a ladybug is mariquita—a reference to the Virgin Mary, who’s associated with ladybugs in many languages, maybe because of the scarlet color she wears in some Medieval and Renaissance paintings. In Korean, the word for ladybug translates to “shaman beetle” because their red tint is similar to a shaman’s brightly colored robes. Do you know of other common names for ladybugs? Drop them in the comments!

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