Pollinator Confidential
A podcast featuring the untold stories of native plants and the pollinators that love them.
Pollinator Confidential
Wasps! Wait--What?? Heather Holm on the Benefits of Wasps
Wasps usually get a bad rap, evoking memories of painful stings. But did you know that the vast majority of them don't bother humans, but instead serve an essential role as nature’s pest controllers. Wasps are carnivorous hunters, and their intended prey are insects–including the pests in your garden! In this episode, Lisa and Pam are joined by Heather Holm, renowned pollinator conservationist and award-winning author, who shines a light on these under-appreciated insects. Heather shares her in-depth knowledge of wasp diversity, nesting, and dietary behaviors, and reveals the fascinating stories of their crucial ecological contributions.
Learn about specific plants that provide wasps with nectar, prey, and shelter, and discover gardening practices that support these vital members of the pollinator habitat.
Hello everyone and welcome to Pollinator Confidential, a podcast featuring the untold stories of native plants and the pollinators who love them.
Pam:I'm Lisa Schneider and I'm Pam Ford, and we are Penn State Extension Master Gardeners from the SchmetzingerS Butterfly Garden Habitat Project, located in Tudyk Park in State College, pa.
Lisa:Well, pam, it's August and you know what that means I sure d.
Pam:IHalloween. Decorations are on the store shelves and pumpkin spice latte is everywhere.
Lisa:Oh goodness, and in my garden the avalanche of tomatoes has begun, which is a good thing, but it also means that we're starting to see more wasp activity and I know I'm on the lookout for them. I'll start to see them on my goldenrod in particular, and also on the fallen peaches from my neighbor's tree, but so they're kind of on the top of my mind at the moment and I thought it would be a good time to talk to somebody who knows a lot about them. We're so honored today to be joined by Heather Holm.
Lisa:Heather is a noted pollinator conservationist and an award-winning author of three books about native plants and pollinators, including Wasps: Their Biology, Diversity, and Role as Beneficial Insects and Pollinators of Native Plants, and her expertise includes exactly what we here at Pollinator Confidential are most interested in the stories of the interactions between native plants and their pollinators, as well as the natural history and biology of native bees and predatory wasps. I first became aware of Heather a few years ago when I saw an excellent online presentation on wasps that she gave (back in the COVID days, when we all had lots of time to stay home and watch online presentations), and I was fascinated by the information that she shared and by her incredible photos. She is a very accomplished photographer and her pollinator photos and educational materials have been invaluable resources for us in recent years and we're so grateful to her for sharing many of those and for the opportunity to speak with you today, heather welcome.
Heather:Thank you, lisa, great to be here.
Pam:So when we give tours we talk about wasps as important residents of the pollinator garden, but many times it's met with a very negative reaction. You've probably had to deal with that. It seems there is always someone who has had a run-in with a ground nesting wasp. Now, even ground nesting bees are a hard sell for us. So I was captivated by the plant insect interaction stories that were profiled in Pollinators of Native Plants. That book, which I carry in my bag it's got a lot of dog ears on it. It really gave me a broader awareness of the wasp diversity and nesting behavior and especially the plant and prey preferences. It was just the diversity was amazing to me. So I wonder what led you to write this wonderful book about wasps?
Heather:Well you kind of touched on it already, so sort of focusing on bees for the first part of my pollinator conservation career. And then, you know, being out in the field and seeing bees nesting in the ground or in cavities, I would come across wasps as well and noted that they have very similar behaviors. You know whether it's excavating a nest in a similar way to bees or provisioning a nest in a cavity. And so I knew wasps were some subset of wasps, were the ancestors of bees, and so I thought ancestors of bees, and so I thought maybe I can change some people's minds by showcasing a small subset of wasps that frequently visit flowers, so starting with the gardening audience and the people who are working around plants, to get some buy-in to their benefit. So that's one reason I wrote the book. I just wrote it thinking that it's something that was needed, not knowing whether it would be well received or not, given what you just said, that people inherently have this fear of all wasps, as you mentioned have been around a very long time.
Lisa:In fact, how did that evolution go? Isn't it true that bees evolved from wasps?
Heather:Yeah, bees evolved from what I'd call the nest building wasp, the predatory wasps. Sometimes they're called stinging wasp, which I don't really prefer that common name for obvious reasons, but they basically, with the evolution of flowering plants around that time, likely switched their diet from an insect-based diet, which wasps primarily feed on insects or spiders, and bees diverged and switched to this plant-based diet that we're familiar with of pollen and nectar. So, really, if you look at the differences between these predatory nest-building wasps and bees, the primary difference is in the type of food that they gather and bring back to the nest to feed their larva. And so that's really what I wanted to highlight for people, that why wouldn't we like the ancestors of bees? Right, they have all of these similar traits and behaviors and they're equally as fascinating.
Lisa:They certainly are. I always tell people with the evolution to think of bees as the hairy, vegetarian, peaceful wasps, like they're the hippie wasp.
Heather:That's a great description.
Pam:So, like bees, wasps are both solitary and social, and I learned from your webinar that the minority of wasps are social wasps. I didn't know that before then. They construct nests below ground and above ground. Heather, you cover the wide variety of nesting behaviors and nest architecture among wasps, so on this topic alone we could do a separate podcast, because I think that was one of my favorite parts of the book was the architecture. One of the stories I found so fascinating is how the paper wasp creates these similar sized cells. Could you tell that story how wasps get those, those paper wasps get those measurements?
Heather:Yeah, this is so interesting, pam.
Heather:The paper wasps are part of the social wasp group of wasps, and the social wasps in North America collect fibers, whether it's wood or plant fiber, mix water and salivary gland secretions and chew that up, ultimately making paper.
Heather:And so their nests are made of the nest cells that look similar to a honeybee nest comb and sometimes the outer envelope. In certain social wasps it's all made of paper, and I'm particularly fascinated in all that extra work that they go to just to create this home and protective space for their larva to develop, and protective space for their larva to develop. So, getting to the measurement part, the inside of a wasp social wasp nest, the combs themselves are made of paper, similar to the ones you see in a honeybee hive, and the wasps, as they start adding layers around a circular tube, they're building it from the bottom up, adding layers of this chewed up fibrous paper-like material. They use their antenna in order to make sure that each cell is of the same size or diameter, and so their antenna are the measurement sticks, in a sense. And then, once that they build circular paper cells side by side, clustered together, they change into that familiar hexagonal shape that we associate with honeybee combs.
Pam:It reminds me of the tools of a sculptor.
Lisa:Exactly, or I think of them as like, I would want a wasp to be my contractor because t hey have so many skills. They can dig, they can do the jackhammering and they can do the raking and they can do the bulldozing.
Lisa:They can do everything--they're HVAC specialists, they can do everything
Heather:true, you know, like you said, those social wasps are adding droplets of water in in the colonies to keep them cool and fanning their wings. And the solitary wasps are using all of these different excavation techniques and we can talk about more of those but some jackhammer like and others vibratory mechanisms to settle mud for a preformed mud nest. So that to me was extremely fascinating, all of these extra behaviors and things that they employ again just to make this enclosure and home for their larva
Lisa:I read that some of the wasps can even like grasp a pebble in their mandibles and use that as a tool to-- What were they doing that for?
Heather:They were, yeah, backfilling a ground nest. Some will grasp a pebble in their mandibles and then pound the ground to tamp the soil.
Lisa:Yeah, Wow, that is incredible. The other thing that really struck me about the nest architecture that many solitary wasps leave a vestibular or empty cell at the end of the cavity tube. I think like as protection against predation, right, and it made me wonder are there any solitary bee cavity nesting bees that do that?
Heather:There are! Some of the bees in the family Megachilidae, which is the leafcutter bee family. They will also sometimes leave a vestibular cell, so it's basically an empty cell at the front or exit of a long, narrow cavity, and so it creates this double wall protection, and each bee or wasp is using different natural materials to create these walls or partitions inside of a cavity nest. So leaving a vestibule I guess helps to keep some of the predator's natural enemies out.
Lisa:Right, well, it makes perfect sense. I just was not aware that there were bees that did that as well. So we learn something new every day, right, pam?
Pam:We sure do.
Pam:A notable difference is that wasp nests are provisioned by prey rather than pollen. Eight years ago I had the opportunity to meet Masa Nomura, and he was a visiting scholar from Japan. He was at Penn State and when he wasn't on the Penn State campus he would come out to our demonstration gardens and take photos of insects. He was a photographer like you. He had all the equipment, the long lens and everything. I was just struck by his knowledge of the insect body parts that he was able to identify as the wasp carried them back to the neck. To me it looked like this little green blob, but he would look at it and tell me what it was. Now that I read about the specialization of prey in different wasp groups, it makes sense. Can you speak to that about the prey specialization? I found that really cool.
Heather:I actually didn't know really how specialized wasp prey was until I started writing the book and researching, you know, different genera and noting what is the prey for that specific species, and I was not surprised, of course, because specialization in the insect world is pretty common. You know, most people think it's rare. They think of the monarch butterfly right specializing, the larva specializing on consuming milkweeds. But across the insect world many, many specializations occur and with the solitary nest building wasps they really have a range of specializations. So they generally are sticking to one insect order.
Heather:So if it was a broad specialization, an individual wasp may hunt various types of flies but they stick to flies alone. And then if there are stricter specialists, some species would maybe only hunt flies from a single genus or, even more narrow, a single species. And we see that in bees as well. Now that we know more about those pollen specializations, anywhere from 20 to close to 50% of bee species that occur in a given state are specializing on a narrow suite of plant pollens, and so to me that that was really interesting from the wasp side of things because you know they're, they're providing these two ecosystem services and the main one, of course, is insect population control and you can imagine, with all of these, this wide diversity of wasp species, each really going out into the landscape and looking for very specific insects to hunt, or sometimes spiders, that they collectively are really controlling a lot of different insect orders and insect populations.
Lisa:They certainly are. It was amazing to me that, not just the specialization, but such a narrow range like --was it the ant queen kidnapper or something where the window of time is so tiny it seems like. Can you tell us about that one?
Heather:right, yeah, the ant queen kidnapper wasp, I think what the one you're referring to and they, the female wasps, just hunt queen ants, and queen ants, uh, are winged and go on these nuptial flights, and it's a very small window of time that they're on the wing out of a nest and doing these nuptial flights, and that is the specific type of ant that this wasp hunts. And so she, obviously, her adult life cycle has to overlap when these winged ants are out doing nuptial flights for them to have enough prey source. So the add on to that story, is she, even though she captures the winged ants with wings, she removes them before placing the ants inside of her nest to feed her offspring.
Lisa:Picky, picky.
Pam:So why she does that? Yeah, exactly, that seems very efficient. It's like when you're roasting a Thanksgiving turkey you have to remove things.
Heather:Right, I'm sure the wings are probably not very digestible. So, removing the gristly parts.
Lisa:Just seems like a lot could go wrong there, you know, wow. Well, so we've talked now about the diet of the larvae and I think most people, When you think of a wasp, will think of that wasp- waist silhouette that wasps have. which is not just a handy ID tool but gives us a clue to the diet of the adult wasp right? which is different than what they're feeding their larvae.
Heather:Right. So wasps as larvae, as you just said, lisa, they are feeding on a pile of insects or spiders that their mother has put inside of a nest for them, and so you can characterize them as carnivorous eating insects while they're growing as a larva. But once they emerge from a nest as an adult, most wasps switch to a primarily carbohydrate-rich diet, mostly in liquid form. So that's where flower visitation comes into play. Many wasps visit flowers to feed on flower nectar. They have a number of other things that they consume that are similar aphid or plant-feeding, insect honeydew or waste plant-feeding, insect honeydew or waste, sometimes tree sap but their diet is more of a liquid diet of carbohydrates as adults. So the exception is some of the social wasps don't really switch to that vegetarian diet as an adult. They tend to be scavengers and continue to feed on different carnivorous meat sources, sometimes dead insects, dead birds etc. So they throw the generalization out the window. I guess you would call it, but that's the way nature works, right.
Pam:You can't generalize. And in reading about the diet of the wasp I was not expecting this reversal of food transfer in the social wasp nest. That blew me away. Now I would expect the transfer of food to the young, but the idea that the larvae providing these larval salivary secretions that would in turn feed the adults. So what is the purpose of this interchange? And if you could tell the story about how the adult pats on the larval cell like knock, knock.
Heather:So the term for that is trophyllaxis.
Heather:And so in a social wasp nest, you know, you have a primary egg-laying female, or sometimes a queen in certain nests, and then you've got a bunch of female offspring sisters who are collectively working in the nest no different than a honeybee hive or a bumblebee colony helping the primary egg-laying female, and so you've got a lot of individuals working within the nest to rear multiple larvae that are developing at one time, and so you have a division of labor where some of those workers or sisters are out capturing prey in the landscape and bringing it back, but you have many of them remaining in the nest doing different types of jobs, such as, you know, just feeding the larva is their job, for example, and so they also need calories, and protein calories.
Heather:And so this very strange exchange of nutrients has evolved, where the larva, as you said, Pam, are secreting sugary substances from their mouth parts and the adult wasps in the nest feed on those, and in exchange they will then feed the larva bits of insect protein. And so it's this really weird exchange, and you think it would be at the expense of the larva, right? Their job, if they had a job, is to consume as many calories as possible while they develop, so that they ensure that they turn into an adult wasp. But this trophyllaxis has evolved as this exchange of nutrients which maybe it prevents the adult wasps from perhaps cannibalizing or eating the larva. They're offering something in return instead of being cannibalized.
Lisa:Please don't eat me.
Heather:Please don't eat me. There are whole books written about wasp sociality and and that whole mechanism of of that food exchange between larvae and adults.
Pam:Well, we both got the book at the same time, and that that section of the book really struck us both as so I had never heard of it. It was just so interesting
Lisa:So it should be clear by now that wasps are amazing creatures and we shouldn't need to justify their existence. But you know, Heather, we are humans, and so we have to talk about some of the benefits that wasps provide to us. You mentioned a little bit about this earlier, but can you tell us more? What are some of the ecosystem services that we rely on them for?
Heather:Yes, so I touched on the big one, which is insect population control, and I like to remind people, you know, if we took all wasps out of the scenario or out of the world, we would be in pretty dire straits.
Heather:Think of all of those different insect populations that are continuously hunted by these predatory wasps, or also the whole parasitic wasp group which we haven't talked about, and a lot of those populations would really get way out of whack and out of control, causing significant, perhaps economic, harm to plants through plant damage.
Heather:So wasps really don't get enough, I think, credit for the role that they play, because it's so subtle and hard to quantify, but they really are providing that important ecosystem service, really are an important providing that important ecosystem service. The the second one is plant pollination through their visitation to feed on the nectar that I mentioned and that in many cases is rather incidental or obviously not perhaps always resulting in pollination. And they're not like bees right, they're not visiting flowers like a female bee to purposely collect that pollen and move it around and take it back to the nest, which would result in a higher probability of a flower being pollinated by a bee. But wasps the way that they interact with certain flowers. You know, based on the flower structure, where pollen is deposited, where the flower's receptive stigmas are located, and how a wasp maybe inserts its head into that flower, they do do quite a bit of transfer of pollen, likely resulting in some pollination.
Lisa:So going back to that first one, the insect pests that they control :Gardeners. Just so you know, they eat things like stink bugs and the emerald ash borer, tobacco hornworms, cabbage loopers, squash bugs (and I really need those in my life. We'll talk more about that in a moment). All sorts of insect pests they control. One of my favorite things, Heather, in your book was the little insets you have with quotes from books of the past, like Margaret Morley's 1900 book Wasps and their Ways. I just love that. I've been reading that book and she says it so well. She says that "the wasps are exceedingly valuable to the agriculturalist, that the wasps are exceedingly valuable to the agriculturalist but for it. The hordes of insects destructive to vegetation might lay waste to the gardens of the earth, even to the discomfiture of proud man himself. And I couldn't say it better myself, margaret.
Heather:Me neither. That was a fun sort of foray into looking at those old texts and and the language is just so beautiful that you know I had to include some of those quotes.
Lisa:It is. It is when she's talking about talking about them imbibing fermenting fruit and she talks about the orgy of drunkenness and how they stagger about. I mean, just the way she puts it is great.
Pam:Now at the Snetsinger Butterfly Garden we've chosen many plants that we understand to be especially attractive to a diversity of pollinators. We have pale Indian plantain, we have five different mountain mint species, lanceleaf coreopsis, several species of goldenrod, boneset, golden alexander, rattlesnake master, and the list goes on. But we also have a very diverse layered landscape of trees and shrubs that bring in those caterpillars that provide prey for many of these wasps. We have elderberry and raspberry canes out there that could be used by a cavity nesting wasp. So can you tell us more about what they're looking for in a plant?
Heather:As far as the attractiveness for nectar?
Pam:As far as the attractiveness for nectar or Overwintering areas, food yeah, and shelter.
Heather:We can start with the food part. So, because they have very specific prey, some, for example, are just hunting the leaf mining caterpillars that you'd find on shrub foliage, right? So that particular wasp would go out and search low you know waist high sort of foliage of a shrub and investigate if there is a leaf mining caterpillar and they will actually like chew the leaf and then pull the caterpillar out. And so their hunting is all based on that knowledge of the prey and they likely are using olfactory cues, first, some certain smells, whether it's they've associated with the smell of the plant tissue as it's being consumed by the prey, or the smell of the prey itself. You think of stink bugs, right? They have their own distinct odors. So they're using a lot of those sensory first and then followed by visual sort of confirmation once they get close to the prey.
Heather:So the we all know that the the caterpillar plant relationship is much like the monarch is a lot of. It is based on specializations as well. So I would imagine a wasp would have very specific needs to, you know, find their prey on specific plants and that would influence the way in which they hunt. So, as you said, pam, having not just firing perennials that you see wasps visiting for nectar. The woody plants play a really important role for their prey searching.
Pam:And the length of their tongue. That determines what kind of plants they will visit, doesn't it?
Heather:It can. Yeah, so those physical traits such as tongue length really will either allow a wasp or some kind of flower visiting insect to access a flower's nectaries or not. Right, they generally are visiting plant families that have flatter or shallower flower forms, so the aster family is a great example. You mentioned goldenrods. Those are flowers that are quite shallow, so wasps that generally have much shorter tongues than most bees are able to easily probe a flower of a short length and access the nectar. They do employ some tricks, much like large carpenter bees, where they will chew a hole in a long flower corolla near the nectary and then insert their tongue into that hole. It's called nectar thievery, so some wasps will employ that if they can't legitimately access the nectar from a more complex flower form.
Pam:And even thieves have a valuable role in the ecosystem.
Lisa:That's right, Now because it's been so so, so dry and hot here, unusually so this summer. We both really picked up on the-- I think you mentioned something about mountain mint, how the little hairs, slow evaporation so that the nectar isn't so viscous and is easier for them to access. Am I correct about that?
Heather:Yes, that's a common trait for some flowering plants to have hairs, which it's believed that it does slow down that evaporation of the water in nectar. So you can imagine, if you had a straw, the difference between drawing up a glass of water versus trying to draw up a glass of honey. Right, honey, right. So once that sugar becomes concentrated it gets quite thick and insects will ultimately lose the ability to be able to draw up a very viscous type liquid.
Lisa:So what is a wasp tongue like, anyway? I mean, with butterflies it's sort of a sponge situation, and bees are more of a sort of a spoon lapping thing. What is a wasp tongue like?
Heather:I would say the tongue is a shorter version of a bee tongue and bee tongues are quite diverse, but generally they have a tip on the end that's like a tasting mechanism. They are drawing up a fluid up through the tongue and into their gut and through their mouth parts of course. So not too different, I would say, from a bee, other than generally they tend to be shorter tongued.
Lisa:Okay, so is there anything else that we can do to provide good habitat for wasps that's unique to wasps, that we wouldn't, you know, be doing for other pollinators already?
Heather:You know there's the similarities for habitat for solitary bees and wasps. I can't think of something that's really really unique, other than perhaps certain flowering plants that you would choose to specifically attract wasps. But for where a lot of these solitary wasps nest, they either are nesting in the ground, like a ground nesting bee would, excavating some kind of burrow. Then a minority around 20% of nest building wasps do nest above ground in the same places that you may find bees. So holes in wood, in standing dead trees or a log lying on the ground, as you mentioned, bramble canes or hollow or pith-filled stems. Some wasps will nest there stems, some wasps will nest there, and then we have wasps that basically do nest above ground but they form their own nests with mud, so they're making these free form nests. So all of those habitat gardening practices that people are starting to employ, such as putting a log on the ground, would support both bee species and wasp species. Or, if you have a enough room, you know, a standing dead tree snag is very valuable habitat as far as the plants are concerned.
Heather:Besides looking at flowers with shallow nectaries, wasps tend to preferentially like lighter colored flowers. Whether they're more visually attractive or what reason, I haven't determined. But, pam, you mentioned Boneset and we've already talked about Mountain Mint or the Boneset and Thoroughworts in the genus Eupatorium. Those are highly attractive flowering plants for wasps. Those are highly attractive flowering plants for wasps, and the rattlesnake master is another one in the carrot family but also white flowering. So they really tend to like these lighter colored flower forms versus really deep, deep flowers, like bees may be attracted to.
Lisa:Now here's my most burning question of this entire interview, Heather. This is really important. Am I doomed? I have heavy clay soil. How can I attract those sand wasps that eat squash bugs? Is there anything I can do? Shall I build them a sandbox in my garden? Is there any way I can that I can bring these beneficials into my garden, cause I need them very badly?
Heather:Yeah, some people have tried that and you know they've basically already had a sandbox whether they had children or grandchildren, and they found wasps nesting in it. I commonly get contacted by municipalities that find big populations of sand wasps in park, volleyball courts and similar places where they brought in a lot of sand. So it would be worth trying. But I mean you'd have to go to so much effort and work just to experimentally see if that attracted them or not.
Lisa:I don't know, At this time of year it seems worth it to me! it might not seem worth it at another time.
Heather:Yeah, yeah, it's so annoying when you put that much work into a particular plant or garden or veggie and then, right at prime time of harvest, yeah,
Pam:Well, unless there's a wasp that takes down a groundhog, I'm out of luck
Heather:. I think groundhogs would be pretty hard to transport.
Lisa:I don't think they could even drag a groundhog. No, well, before we wrap up, Heather, can you think of anything else that we haven't covered that you would like to highlight or talk about?
Heather:I just yeah, I want to mention back to the stinging. We touched on this, and Pam mentioned it. You know it's a very, very small minority of wasps that have a social nest that are likely to sting you if you disturb the nest, and so it's important for people to know you know 95% of nest building wasps out in your garden and landscape doing their thing, hunting their prey, making their nest. They are not going to defend their nest or sting you. I mean, don't pick them up in your hand and try and squish them, you'll get stung. But we, you know people rarely have any kind of negative interaction with the vast majority of wasps and I think partly they go largely unnoticed because of that right, we only remember and think about and associate with some type of wasp we've had a negative interaction with. So I just want people to know you have a large diversity of wasps in your garden right now. Go out there and discover them and appreciate them and know that they don't pose a threat.
Lisa:Yeah, I'm so glad you highlighted that, Heather, because we we do have a negative bias, don't we-- Always remembering the negative interactions, but there are so many unseen helpers out there all the time, and they include wasps. So I think we can all agree that wasps are unfairly profiled and underappreciated and, listeners, I hope that you, like us, have a new appreciation for them. It's been such a pleasure to talk with you today, heather. Thank you so much for making the time and, listeners, be sure to check out Heather's website pollinatorsnativeplants. com to find out about her wonderful books and photos and plant lists and so many other wonderful resources that she has there for us.
Pam:And Heather's book Wasps: their Biology, diversity and Role as Beneficial Insects and Pollinators of Native Plants is an exceptional resource. The photos are so descriptive and it's very, very clearly presented. Information and speaking of resources, we're excited to announce that our new Snetsinger Butterfly Garden website is nearly ready for launch. We've updated everything with more information than ever, new directories and photos of plants and pollinators. We've added a wasp section because this book inspired us so much. We realized we need to put wasps in our directory Lots of planting resources and so much more and stay tuned for the official launch.
Lisa:Right. Make sure to be checking that out as well, snetsingerbutterflygarden. org and let us know what you think after the launch occurs. We hope that all of you enjoy the rest of your summer and keep an eye out for our wasp friends out there. And be sure to join us next time for more Pollinator Confidential.