wasps

The Shared History of Wasps and Bees, And How Bees May Have Become Vegetarian

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We may have all found ourselves in that situation in which we see an insect on a flower and we wonder whether it is a wasp or a bee, and we may have also seen people panic when they encounter a bee, thinking that it is indeed a wasp. Although the two groups are very distinct and there are several ways of telling them apart (check out this previous post to see how to do it), this difficulty is in part a signature of the shared evolutionary history that the two groups have. In today’s post, I want to tell you about the evolutionary origin of bees, how it is interwoven with that of wasps, and how evolutionary studies can help us understand and explain the diversity of our charismatic bees.

Evolutionary histories and the big family we are all part of

Before jumping into the main topic of this blog, please bear with me so I can give you a bit of context for what I’ll tell you, and so you can fully appreciate the power of the discoveries I will tell you about in just a second. One of the foundations of today’s biology and the way we understand life is that living organisms share a common ancestry and that evolutionary processes such as natural selection, mutations, dispersal, and random processes have led to the establishment of new lineages that can evolve into new species and new groups of organisms. What this means is that all the living organisms we know can be placed in a sort of genealogical tree, where more closely related species and groups appear placed on branches of the trees that are also closer to each other (we call these trees “phylogenies” or “phylogenetic trees”). Also, this means that if we were to take these trees, and we were to follow the evolutionary process “backward” (from the tips to the internal branches; that is, from the present into the past), we would be able to identify branching points, which represent the now extinct ancestors of species we know today.

a diagram of a family tree
A phylogeny can be compared to a genealogical tree we may want to build for our family. In this tree, the most closely related members of our family share recent ancestors (marked with diamonds), but are still connected with more distantly related members of the family with longer branches and other more ancient shared ancestors. In the same way, a phylogeny represents the relationships between species or groups of species, with branches connected by their shared ancestors. Image: University of Iowa

Although this may sound like a biological nerd moment of mine, I hope that you will appreciate the enormity of this principle. This simple concept indicates that each of us and all species that exist on the planet have shared ancestors at some point in our history. We are all related to each other, like a huge family… and as for all families, the study of our history can teach us fun and interesting things about who we are, helping us understand and explain things we observe today. Let me tell you what the study of these phylogenies has taught us about wasps and bees (and their shared history) and why this excuses us in part from not always being able to tell them apart 😉.

Bees and wasps, and the vegetarian wasp

As you may know, bees and wasps are both insects that belong to the order Hymenoptera. Despite the fact that people knew they were related but distinct from each other, it was not until relatively recently that people understood what that relationship was. In fact, because they share a lot of common traits, scientists were for a long time confused about what the most closely related group of Hymenoptera was for bees, wasps, and ants. Some years ago, with the development of new methods that allow for more detailed studies of phylogenies, researchers found strong evidence that ants are a group of organisms that is related but distinct from another group formed by bees and by a particular group of solitary and usually ground-nesting wasps called crabronids. Besides the taxonomic and purely conceptual importance of this discovery, what this meant biologically was on the one hand, that bees are evolutionarily extremely closely related to wasps, to the point that we could consider them “non-carnivorous wasps”. On the other hand, this discovery showed that all bees we know today would have evolved from a wasp-like ancestor that was solitary and ground-nesting, like the crabronids we know today.

a family tree of bees and wasps - showing evolutionary relationships
In 2017, Branstetter and collaborators used phylogenies to demonstrate that all bees and a group of wasps (crabronids) shared a common ancestry, indicating that bees can be considered a type of “vegetarian” wasp. In the figure, the position of the common ancestors is shown with arrows and stars. The main groups are labeled on the left. Image: modified from Branstetter et al., 2017

If you’re like me and find this fun, keep reading because it gets even more fun! 😊 So, after this discovery, the people who work on these topics wanted to know more. For example, can phylogenies tell us more about how the transition from a meat-based diet (wasps are carnivores) to a pollen-based one (bees feed mostly on pollen and nectar) could have happened? To investigate this, researchers ran a similar analysis, but this time considering a lot more species of both bees and crabronids. Constructing phylogenies using genetic information, they figured that when the evolutionary relationships of these groups were studied, it appeared that bees were the most closely related to a particular group of crabronids that is known to predate on thrips (a family called Ammoplanidae).

a closeup of a small black bee
Bees have been shown to be very closely related to a group of tiny wasps in the family Ammoplanidae which are known to hunt on thrips. Photo: CBG Photography Group (CC).

Besides confirming the discoveries of the previous study, this one provided a logical and interesting biological and ecological context for the transition from carnivory to pollinivory in bees. Thrips are a group of insects known to feed on plant materials, often found on flowers, where they feed on pollen. This new study proposed that a possible evolutionary opportunity may have appeared when a lineage of thrip-predating wasps evolved the ability to not only digest thrips meat but also the pollen they contained in their guts (!!). This transition could have set the evolutionary foundations to eventually transition to a diet fully based on pollen, which opened opportunities to the newly emerging lineage to feed on a new dietary resource not already in use by other wasps. If this is true, this transition would have provided an important evolutionary advantage (e.g., reduced competition for food), which would have led to the huge diversification of bees, leading to the extreme diversity we see today.

By Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park. See more posts by Anahí.

Anahí also writes an Extension Blog in Spanish! Check it out here, extensionesp.umd.edu, and please share and spread the word to your Spanish-speaking friends and colleagues in Maryland. ¡Bienvenidos a Extensión en Español!

Q&A: How Can I Get Wasps Out of My Compost?

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Yellowjacket (Vespula sp.). Photo: M. Talabac

Q:  Wasps took up residence in my compost pile this year. I could avoid them for a while, but I’m hoping I can use the pile again next spring. How can I get them out of there?

A:  Ground-nesting yellowjackets are probably the culprit here, and the good news is that they will disappear on their own by winter. In our area, social wasps like hornets, yellowjackets, and paper wasps don’t reuse the same nest for more than one year. By late autumn or early winter, the old queen, workers, males, and any juveniles that did not have time to mature will all die. Only mated young queens survive, leaving the nest of their birth to disperse and overwinter in a sheltered spot by themselves. They seek out insulated spots like hollows under fallen logs and nooks in stone walls, go into the insect version of hibernation, and emerge in spring as it warms up, each flying off to find her own site to start a new nest. She does all the nest-building and larvae-feeding work by herself until the first generation of young matures, so she has a limited ability to defend it from disturbance.

Nest remnants left in the compost pile will be abandoned (or will at least contain dead wasps) during winter, when you can safely dig it out for removal or just leave it to compost with the rest of the pile contents. Wild animals can also tear apart abandoned wasp nests, looking for easy-access morsels to snack on, though this presumably happens more regularly with visible above-ground nests.

Preventing a new generation of wasps from choosing the same appealing nest site in a future year might be challenging unless you enclose the pile in insect mesh or something to discourage queen wasps from exploring it in spring. Regular turning of the pile – recommended to keep it well-oxygenated anyway – might disturb a new queen too much to allow her to successfully begin a new nest.

By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Miri writes the Garden Q&A for The Baltimore Sun and Washington Gardener Magazine. Read more by Miri.

Have a plant or insect question? The University of Maryland Extension has answers! Send your questions and photos to Ask Extension. Our horticulturists are available to answer your questions online, year-round.

Cicada Killer Wasps Are Scary But Good

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a close-up view of a cicada killer wasp showing its light yellow and black striped abdomen
Cicada killer wasps are good pollinators who keep cicadas in check.
Photo: Dawn Dailey O’Brien, Cornell University

It’s big. It’s creepy. It’s the cicada killer wasp and it has some local folks worried. But it’s a good guy. Honest. 

Looking like yellowjackets on steroids, 2-inch-long cicada killer wasps are yellow and black and a bit intimidating. But it’s all a show. 

Unless you’re a cicada, you have no worries. These wasps help control the annual cicadas buzzing in our trees.

In fact, male cicada killer wasps don’t have stingers at all and females aren’t likely to sting unless you step or sit on one.

In addition to their ginormous size, cicada killer wasps worry folks because they do figure eights over lawns, looking like they are Up To No Good.

Nope. Those are just males establishing or defending territory. Boys will be boys. 

The dudes have been hanging out since July, scoping out territory while waiting for the ladies to arrive. Their manly posturing results in often spectacular wing-whirling combat, all bluster and bluff.  

Check out the video of a close encounter with University of Maryland entomologist Mike Raupp’s Bug of the Week feature.

Following a brief romantic interlude, the female cicada killer wasp digs a finger-sized nesting chamber in the ground, leaving telltale piles of excavated soil.

Then she climbs trees in search of the cicadas which she uses to feed her young. 

When she finds a cicada, she stings it to paralyze it, then flies the cicada down to the ground, dragging it to her nest. This is no mean feat since cicadas are much larger than she is. That’s one determined mama.

She stuffs the cicada into her nest, lays an egg on it, and seals the opening. When the egg hatches, the larva will chow down on the cicada which is, unfortunately, still quite alive. Ah, the circle of life.

Well fed, the larva will wrap itself in a case, pupate and stay underground before emerging as an adult next summer. 

Interestingly enough, female cicada killer wasps can choose the sex of their babies. If they give them one cicada as food, they turn out to be boys. Given two cicadas, they become larger females.

A female cicada killer wasp’s work is never done. As soon as she seals one nest, she makes a new one and goes cicada hunting again, helping to keep their population in check.  

See female cicada killer wasps in action in this Bug of the Week profile.

Cicada killer wasps also are good pollinators, moving pollen from plant to plant as they feed on nectar as adults.  

Cicada killer wasps congregate around some petunias.
Photo: John Lefebure

What should you do if you find cicada killer wasps in your yard? Not a thing. Tolerating them is best since they’re only around for a few weeks and are beneficial. Chemical controls are not necessary.

But if you’re bothered by the holes they make in your lawn, wet down the area with a sprinkler.  Cicada killer wasps don’t like to build nests in moist soil.

They also avoid nesting in dense lawns. So their nests are a clue that your lawn may need some beefing up.  

Cicada killer wasps may be big and a little scary looking. But I hope you’ve gained some appreciation for these fascinating insects and enjoy watching them dance over your lawn.  

By Annette Cormany, Principal Agent Associate and Master Gardener Coordinator, Washington County, University of Maryland Extension.

This article was previously published by Herald-Mail Media. Read more by Annette.

 

Are Baldfaced Hornets Friends or Foes?

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Distinctive white marks on their heads give baldfaced hornets their name.
Photo:  Johnny N. Dell, Bugwood

It’s been a good year for baldfaced hornets. Many people have contacted me to report their grey papery nests in trees or hanging from the eaves of their homes.

So, are they good guys or bad guys? Do they need to be controlled? It’s a matter of making an informed choice. So here are the facts.

First, baldfaced hornets aren’t hornets at all. They’re black and white yellowjackets that nest in trees, shrubs, and on buildings. Since they kill many harmful pests, they are considered beneficial.

It’s only when their nests are nearby that they pose a potential threat from stinging. Left alone, they tend to be benign. They usually only sting to defend their nests. I’ve had several walk up and down my arm peaceably. 

The white marks on their head earn them their “baldfaced” moniker. Workers measure about three-quarters of an inch long and queens are slightly larger.

In the spring, overwintering queens emerge from tree bark, stumps, logs, rock piles, and other protected spots. Each queen builds a small nest with a few brood cells, lays eggs, and gathers insects to feed the growing workers.

When those workers become adults, they take over the housekeeping duties, building and taking care of the nest, foraging for food, and tending to the growing family from eggs laid by the queen.

Baldfaced hornets’ football-shaped nest is an engineering marvel. To that first handful of paper cells, workers add layer upon layer of hexagonal combs similar to those of the honey bee.

Continue reading →

These Wasps Are Not Social Distancing!

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two yellowjackets
Yellowjackets. Photo: Arlette/Flickr

Wasps are some of the most highly disliked insects and are often all linked together with bees as being “bad”. When my co-workers and I led a group of elementary school children on a bee lesson, our very first question for the group was: how do you feel about bees? Give us a thumbs up, thumbs down, or tilt your thumb to the side if you aren’t sure.

Many times students gave us a thumbs down or to the side with a sad story about being stung or a family member being stung. After letting the children talk, we found that the majority of the time, people were being stung by wasps and not bees.

Social wasps are listed in the family of insects called Vespidae, which includes the yellowjackets, baldfaced hornets, and paper wasps. All of these are aggressive stinging insects that we see in our yard and garden. Social refers to their nesting habits. Several wasps live all together in one nest and will defend that nest, which is why people get stung if they get too close. Social wasps make their nests from paper, which they make by chewing on wood, newspaper, or cardboard.

Paper wasp nest. Photo: A. Bodkins
Paper wasp nest in a pipe. Photo: A. Bodkins

It is important to know that not all wasps are social wasps and they are not all aggressive. Some, like mud dauber wasps, are solitary wasps. They are not aggressive because they do not have a colony to defend. Cicada killer wasps are solitary wasps also. They are aggressive towards cicadas (their food of choice), but not people, unless the female wasps are deliberately provoked.

In the social wasp group, yellowjackets are scavengers and will search widely for food, which includes garbage and carrion. These are often the pesky critters that try to get into your food at picnics. They can nest in the ground and will get aggressive if disturbed.

Social wasps get a bad reputation because of their ability to repeatedly sting. Many people can have an allergic reaction to their venom.

It is worth noting, however, that wasps have a valuable role in the environment — they are predators and even help with pollination. According to the North Carolina State web article on social wasps, a colony of 200 yellowjackets can eat 5,000 caterpillars in just one season.

yellowjacket nest hole in the ground
Ground nest entrance of eastern yellowjackets. Photo: Mohammed El Damir, Bugwood.org

Even though social wasps are considered beneficial insects, you should not feel guilty if you have to remove a nest if it is located in an area that poses a threat to human well-being. Always be cautious when using pesticide products such as aerosol wasp and hornet sprays. These can get into your eyes or on a location that is not intended, such as on pollinator plants, vegetables, or on picnic tables or outdoor dining furniture. Consult and follow the label for correct and safe use. You also can flag or mark the nest entrance and talk to a pest control company about removing it.

All social wasps produce an annual colony that will be destroyed with the killing frosts of fall. So, if a nest is in an out-of-the way location, just leave it alone.

Before taking any action with wasps (or bees), identify the insects first. Check the Home & Garden Information Center website for information or submit your photos to Ask an Expert for identification.

For more information, check out these additional resources.

By Ashley Bodkins, Senior Agent Associate and Master Gardener Coordinator, Garrett County, Maryland, edited by Christa Carignan, Coordinator, Home & Garden Information Center, University of Maryland Extension. See more posts by Ashley and Christa.

Like Figs? Thank a Wasp!

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Last month I wrote about wasps as generalist pollinators (The Buzz on Pollination is Not All About Bees: Wasps Are Pollinators Too!). Today, let’s look at a very specialized type of wasp and its role in pollinating fruit.

Do you love dried figs as much as I do? Well then, thanks to tiny wasps are in the order! In fact, through their evolutionary history, fig trees established a pollination system that is among the most fascinating that exist. Even though we eat only a very small number of them, there are hundreds of fig species, and each one is pollinated by one or a few species of tiny wasps from a family called Agaonids.

fresh and dried figs
Dried and fresh figs. Photo: Pixabay

These wasps are specialized in pollinating fig flowers, with a type of pollination interaction called ‘nursery pollination’. In this type of pollination, the wasps offer the service of pollination in exchange for a place to raise (‘nurse’) their offspring. But how does this work?

Let’s start by saying that a fig is like a sunflower that has been turned into itself, with all their tiny flowers facing to the inside of the fig. Some of these flowers are only female (those will make seeds), and some are only male (they offer pollen).

When visiting figs, the female wasps enter and find the female flowers. Using their long ovipositor (their organ for laying eggs), they lay one egg in it. After doing so, they take some of the pollen they previously collected on the male flowers of a different fig and they actively push pollen into the flower. While doing so, they make sure that the female flower is pollinated, and that the flower tissues grow and mature, which is what their offspring will eat while they develop inside the flower. When the offspring emerges from what was the flower, they reach to the male flowers and collect pollen, after which they leave the fig and start searching for a different one to start the cycle again.

fig fruit
Fig fruit. Photo: Pixabay

Now, you may be thinking that this system can’t work. If the offspring eats all the female flowers (where seeds are!), then the plant has none left for their reproduction! You are right!

Well, it turns out that the plants have found a way around. Among all the female flowers available to the wasps for their egg-laying, some are short and sterile, and some are long and fertile. While the short ones are the ones that wasps can develop in, the long ones will not lead to any larval development.

The female wasps can’t know which one is long or short, so they just try to lay eggs and pollinate all the female flowers. Only some of their offspring will survive. By doing this, the plant sacrifices some flower tissue in exchange for the pollination of all the fertile flowers.

If nobody cheats, both the plant and the wasps benefit from the interaction, with the wasps having a safe place for some of their larvae to develop, and the plants having a safe means for pollen transfer and seed production. Isn’t pollination fascinating?

fig wasps
Fig wasps entering the fig through the fig ‘entrance’ – the ostiole (left). Female fig-wasps laying eggs within the figs (center) and later emerging from the sterile female flowers (right).

And to end this blog today, let me tell you a story. It turns out that most fig species are tropical and subtropical, and thus there are not many fig species native to the continental US. However, we love figs, and thus farmers from California decided to try to produce figs there since the climate is very appropriate for fig tree growth. These fig trees that we eat are from varieties of the species Ficus carica, originally from the Mediterranean/Middle East.

At the end of the XVIIIth Century, farmers in California were trying to produce figs, but with little to no success. Eventually, researchers realized that those cultivated figs did not produce fruit if the flowers had not been pollinated. Wasp pollinators were needed to accomplish that. By the end of the XIXth century, the wasps associated with Ficus carica in their native Mediterranean range were imported and introduced into the USA. Figs containing larvae of the wasp species were then left in baskets close to the planted fig trees, letting the females emerge from the figs and pollinate the cultivated Californian trees. After doing this, the fig production picked up, and today a similar technique is still used in those varieties of figs that need pollination for fruit set (for example, the Smyrna and Calimyrna varieties). Today, California is the world’s third top fig producer. Talk about the economic value of pollinator wasps!

By Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park

The Buzz on Pollination Is Not All About Bees: Wasps Are Pollinators Too!

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Last time we talked about pollinators (see Is This a Pollinator? Five Types of Pollinating Insects You Can Find in Maryland), we received some questions about wasps. Do they also pollinate? If they do, what do they pollinate? So, let’s talk about wasps!

Besides being super important for controlling pests, since most of them are predators, wasps also can contribute to pollination. In some cases, that pollination is so specialized that plants won’t be able to set fruit if the wasps are not around! But don’t let me get ahead of myself… let’s start from the beginning. What are wasps and how to distinguish them from bees?

Is this a wasp or a bee?

Are you confused about the differences? That’s normal! It’s because bees and wasps are closely related and, in the same way that we tend to look like our close relatives, wasps and bees look similar as well. Like bees, wasps have a lot of diversity, displaying different shapes, sizes and colors. Also like bees, wasps can be social (like hornets or yellow jackets) or solitary (like those that make little mud vases or that dig small burrows in the ground).

Wasps in Maryland
Some wasps from Maryland, which can be sometimes seen visiting white/yellowish flowers. Left: Mason Wasp, Pseudodynerus quadrisectus (photo M. McMasters); center: Ringed Paper Wasp, Polistes annularis (photo: Kieschnick); right: Potter Wasp, Eumenes

Taxonomically, there are two groups of wasps: those that have a wasp waist, and those that don’t. Because the former are the ones that we usually refer to when we think of wasps, let’s focus on those. When we think about those wasps, wasps tend to be less hairy than most bees and tend to fly with their legs extended. The legs of bees are usually wider than those of wasps, and while they fly one can see bees rubbing their legs with one another to transfer pollen, while this will not be the case with wasps. Finally, most social wasps fold their forewings when they are at rest, which makes the wings look long and thin.

bee versus wasp
General morphological differences between wasps and bees. Wasps tend to have thinner legs and are less hairy than bees. Wasps also tend to bend their wings longitudinally when at rest.

What do wasps pollinate?

Wasps are involved in different types of pollination interactions, with many being generalists (they visit many different types of flowers) and some very specialized (involving only a very small number of plants).

Generalist wasps

Even though the vast majority of wasps are predators (they prey on your garden pests!), they also need to supplement their diets with sugar, which is eaten by adults but is also required for the proper development of the offspring. For this reason, many solitary and social wasps visit flowers and collect nectar throughout the flowering season, but in particular during the fall, when other sources of sugar become harder to find. During those visits, they often enter in contact with the flower anthers (the flower part where pollen is presented), and thus passively collect and then transfer pollen when they visit another flower.

Most of these wasps have very short tongues, so they are only able to obtain nectar from flowers that are not too deep. Further, most of these wasps can’t see red colors but can see UV light. Because of all this, most flowers wasps visit are open and not too deep, and white- or yellow-colored. If you would like to attract and observe these pollinators and biological control agents, you can plant flowers of the Apiaceae family (carrot and parsley family) and you won’t be disappointed!

Specialized wasps

In addition to generalist wasp pollinators, there are some very specialized wasps that only pollinate specific types of plants. Next month, we’ll take a closer look at specialized wasps and the ones in particular that are essential for pollinating some delicious fruits — figs!

By Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park