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Wasps: Garden friends or foes?
by Blake Layton


Some species, such as the braconid wasp pictured here, are parasitoids. The female wasp lays eggs in a range of hosts such as tomato or tobacco hornworm caterpillars (shown in inset photo). The developing larvae feed inside the unlucky caterpillar before emerging and spinning cocoons. A short time later the wasps will emerge from their cocoons and the weakened caterpillar will die.

When most people think of wasps, they think of paper wasps, and they probably think of them only as pests because of unpleasant past encounters with these stinging insects. However, the world of wasps is much larger and more complex than this!

Our gardens abound with hundreds of species of wasps that vary greatly in size and life habits. Most of the wasps in our gardens are tiny, parasitic species that do not sting people and go largely unnoticed. These are definitely friends because they help control pest insects. There is also a group of wasps known as sawflies whose larvae look like caterpillars and feed on plants. These are usually foes because they damage landscape plants. Two other groups of wasps are the social wasps, such as paper wasps, and the solitary wasps, such as mud daubers and cicada killers. Wasps in both these groups are capable of stinging, and they definitely qualify as foes when they do so, but paper wasps also have a beneficial side.

Most gardeners are familiar with two common types of paper wasps: The small brown and yellow banded wasps, often called guinea wasps, and the larger red and black wasps most gardeners know as red wasps. Actually, there are several different species within each of these types, and to further complicate matters, guinea wasps are often incorrectly called yellowjackets. Yellowjackets belong to a slightly different group of social wasps, and the yellowjackets we have in the South usually build their nests in the ground.


The guinea wasp on the far left has brought home some “caterpillar burger” to feed to the hungry larvae.



The domed white cells of this guinea wasp nest contain maturing pupae, and you can see larvae peering out of some of the open cells. Look closely and you will see a small white egg in the bottom of some of the center cells.


Wasp nests are easiest to control early in the season when there are only a few adult wasps. The aerosol wasp sprays work well, but be careful; there is always a risk of being stung when dealing with wasps.

Paper wasps live in communal nests usually with one reproductive female or queen and dozens of female workers. The papery nests are built of wood pulp the workers collect using their strong mandibles. Paper wasps build their upside-down-umbrella-shaped nests in sites protected from direct rainfall: under eaves, in dense shrubs, in that fertilizer spreader hanging on the back of the tool shed and similar places. These nests do not survive the winter.

Paper wasps overwinter as mated females in protected sites such as hollow trees, attics or wall voids. Overwintered females emerge in the spring and begin building a nest, and successful nests grow larger as the summer progresses. That nest in the fertilizer spreader may contain only one or two adults in April, but by late summer, when it is time for that end of season fertilizer application, it may be as big as Granddad’s straw hat and contain dozens of wasps. What a nasty surprise! “Experienced” gardeners know to check for wasp nests before moving infrequently used equipment, pruning shrubs or working in areas where wasp nests might occur.

Female paper wasps are equipped with venomous stings, which, unlike the stings of honeybees, are not barbed, allowing them to sting repeatedly. Wasps do not go looking for people to sting but will readily attack if they feel their nest is being threatened. Paper wasps have a Jekyll and Hyde personality. When encountered as individuals out foraging for prey or wood pulp, they are not aggressive and rarely sting, but their attitude is much different when their nest is disturbed. Wasp stings hurt, and some people are more sensitive than others. Wasp stings can even be life-threatening to a small percent of people who are hypersensitive.

Both bees and wasps feed on plant nectar, which is loaded with sugary carbohydrates but has little protein. Bees meet their protein needs by collecting pollen, which they carry back to their nests in special pollen baskets on their legs or abdomen. Wasps cannot collect pollen because they do not have these pollen baskets and their bodies are not hairy like bees. This is why paper wasps are not good pollinators. Social wasps meet most of their need for protein by preying on other insects: catching them, chewing them up and carrying these little balls of bug burger back to the nest to feed their young. This is where their beneficial side comes in. Paper wasps are voracious predators of caterpillars and play an important role in the biological control of many caterpillar pests.

As a graduate student at LSU, I was involved in a research project to evaluate the effects of insect-induced defoliation on soybean plants. Our plan was to artificially infest the plants, which were growing in large outdoor pots, with soybean loopers to achieve varying levels of defoliation. This technique had worked quite well in previous greenhouse experiments, but when we placed our young caterpillars on these outdoor plants and came back to check on them the next day, they had all disappeared. We released more caterpillars the following day and waited around to see what was happening to them. Paper wasps appeared by the dozens, methodically searched our plants and removed every caterpillar! In the end, we were forced to place a screen cage over each plant to protect our caterpillars from the paper wasps.

In this case, we viewed the wasps as foes because they were interfering with our research, but most gardeners and farmers consider wasps as friends when they are preying on caterpillar pests. Some organic gardeners and farmers even place special structures in their landscape to encourage wasps to nest there and help control caterpillar pests. Of course, they place these structures in out of the way places where they will not accidentally disturb them during the summer.

In the end, the answer to the question: “Paper wasp, friend or foe?” depends on where you encounter the wasp. Is she away from the nest foraging for prey or on the nest around the tool shed? Wasp nests built in places where people are likely to come in close contact with them are definitely hazards and should be eliminated as soon as possible, preferably while they are small. Most gardeners keep a can of aerosol wasp spray handy for this purpose. It is good to know paper wasps have a beneficial side, but this knowledge will not lessen the pain of their stings.


Happy hour for wasps? This red wasp and yellowjacket are indeed imbibing
the alcoholic flux oozing from this tree wound.

 

From State-by-State Gardening June 2009.
Braconid wasp photo by John Tann.
All other photos courtesy of Blake Layton.

Posted May 2013

 


Dr. Blake Layton is Extension Entomology Specialist at Mississippi State University.

 

       

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