wasps

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!

Maryland Grows7 Comments

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!

Maryland Grows2 Comments

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