Cavity Nesting Bees and Wasps

How do local plants influence the reproduction of cavity nesting bees and wasps?

The city of Cleveland owns a lot of grassy vacant lots (over 20,000!) and these lots are very expensive to manage. During one year, it costs Cleveland around $3 million to mow all the vacant lots throughout the city! But, what if we could plant something different than grass in these lots?

Native prairie plants require less mowing, can grow beautiful flowers, and support urban biodiversity. If we managed all of Cleveland’s vacant lots with prairie plants instead of grass, we could potentially save the city a lot of money which could be used for other important projects like rebuilding roads, updating sewer systems, etc. Pocket prairies can also help combat biodiversity loss and conserve beneficial insects within Cleveland. Beneficial insects include pollinators (bees and butterflies) that help plants continue to bloom and produce crops. Likewise, beneficial insect predators help control pests like mosquitoes, stinkbugs, and other insects that eat crops. When we support beneficial pollinators and predators in Cleveland, we can help Cleveland’s urban farms continue to produce food, and reduce the number of pests in our neighborhoods.

However, there are many different prairie plants that we could grow in Cleveland’s vacant lots. How do we decide what plants are cheapest to manage but still look nice and support beneficial biodiversity? This research compares five different plant combinations for both their appearance and their ability to support cavity nesting bees and wasps.  How successful these plant combinations are is determined by comparing what bees and wasps fly through and/or nest in each of the five habitats. As cavity nesting bees and wasps are important pollinators and predators this project has great potential to enrich Cleveland’s urban farms and neighborhoods!

Note: Cavity nesting bees and wasps are solitary insects that nest in small holes in wood or plants. Females lay individual eggs inside these small holes with either a pollen meal (bees) or an insect meal (wasps).  Cavity nesting bees and wasps are essentially harmless to humans. They do not form colonies or swarm people. These insects are non-aggressive and often very small. If you accidentally disturb their nest, these bees and wasps will try to fly away and will not attack you. I have been working closely with these types of insects for about five years and have never been stung!

How is this research conducted?

PLANTS: Each month, we monitor how well our plants are growing in the vacant lots and complete a vegetation sampling. We document all flowers in bloom, the height of different plants, how dense the plants are, and what species of plants are most common in the lot. You may see us place a rope grid in the lot while we monitor what plants are growing.

We seeded many different plants during the beginning of this research. However, prairie plants take a long time to grow because they develop very long roots before they grow above the soil. When we observe what plants are growing in each lot, we are evaluating how well our seeds have grown and how difficult it is to manage these plants in Cleveland.

INSECTS: We also collect different beneficial bees and wasps that fly through the lots and/or nest there. We use three different insect traps to collect bees and wasps. Malaise traps look like small mesh tents and trap all the insects which accidentally fly into the tent. Yellow pan traps are small yellow bowls that are filled with soapy water. Bees and wasps think that the yellow bowls look like flowers and are trapped in the water.


(Photo: Example of a trap nest.)

We use trap nests to monitor cavity nesting bees and wasps. These nests look like bird houses and use cardboard straws to provide a small space for the bees and wasps to nest in. We do not add insects into the lots, we take away what has nested. When we take the cardboard straws back to our lab, we X-ray them so we can count the larvae inside the straws and see how many offspring each bee or wasp has.

When we collect bees and wasps flying in the lots, we can use this information to discover what species currently live in Cleveland and how abundant each species is. Trap nests, on the other hand, let us know how successful some of these bees and wasps are in reproducing and if our plant combinations contribute to greater reproduction.

Samples are collected from the following Treatments (1,3,4,5,6) : Urban standard (control), Low-growing lawn, Flowering lawn, Native Ohio grasses, and Low diversity pocket prairie.

Trap nests were installed on April 29th, 2016 and removed on September 1st. The first or second day of each month inbetween, we checked the traps and removed all bees and wasps nesting in the traps.

We visit each lot at least two more days each month (June-August). On one day, we collect insects with malaise traps and yellow pans. On the second day, we observe what plants are growing in the lot.

What impact will this research have? 

At the end of this research, we will be able to recommend which plant combinations Cleveland should grow in their vacant lots instead of grass. In the next 5-10 years you may see that many of the grassy lots in your neighborhood are planted with beautiful pocket prairies instead. We hope our vacant lot recommendations will also help Cleveland save money that could be invested in other community development projects and infrastructure that will help Cleveland grow into a stronger, more beautiful city.

This project is lead by Katie Todd. Katie studies Entomology at the Ohio State University and is from Connecticut.

Katie, on the significance of this research:

“This study is interesting to me because even though we often think of conserving biodiversity in the rainforest or in a national park—urban conservation is important too! Studies in Europe have shown that rare insect species can live in urban areas and that vacant lots can provide essential habitat for urban conservation.

I also wanted to work in Cleveland’s vacant lots because I like to contribute to win-win situations where both people and the environment are healthy and able to thrive. I hope that our work helps:

(1) More urban residents have access to diverse, beautiful green spaces and the ecosystem services they support (storm water control, pollination, pest-suppression).

(2) Urban biodiversity, and especially pollinators, continue to grow in Cleveland and contribute to greater environmental quality.”

This material is based upon work supported by the National Science Foundation under Grant No. 1253197.

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.