Thanks for contacting us about the ongoing bee and wasp activity at the community garden. I hope that the following information will clarify the behaviors you’re seeing.

The most aggressive stinging wasp is the western yellowjacket. Their nest is always hidden, usually underground. They rebuild new nests every year. Nest entrances can be holes in the ground, ground openings where stones, boards, or other structures meet the ground. They feed their young carrion, dead insects and are the common pest after our food at a picnic table – enjoying easy food like meat and fruit. They are not pollen feeders, are not usually found by flowers. They can feed on honeydew or nectar, so might be found where there are aphids excreting honeydew, plus ripe fruit for the sweetness. They are most aggressive when their nest is threatened. You may want to check the boards at the base of the plots, and in the rocks that surround the garden for entrance holes. It’s hard to find their nest unless you follow the yellowjackets frequently to find the entrance hole where they are feeding their young.

Another very visible stinging wasp is the European paper wasp. It’s not as aggressive as the western yellowjacket, and builds paper nests that hang under eaves, inside large holes in fences or pipes, or inside abandoned birdhouses, etc. These two insects look similar (especially when moving fast!) – I find it easiest to differentiate by the long hind legs on the European paper wasp that hang down while they fly. They are a non-native predator of insects (primarily), so they often hunt for caterpillars on the cabbage family or flowers. Like the western yellowjacket, they are most aggressive when their nest is threatened.

Stinging incidents often occur when nesting areas of these social insects are disturbed or threatened. Bees and wasps can also be attracted to, or may react to, odors in the environment. Scented soaps, lotions, etc. are examples. Drinking sweet or flavored drinks. If you remain calm when a bee or wasp lands on your skin to inspect a smell or to get water (like our sweat), wait for it to leave on its own or slowly and gently brush it away. Swatting and swinging arms can cause the insect to send pheromones to others in defense, and the agitation increases. Insect repellant applied to your skin or clothing won’t deter these stinging insects.

Note that the traps only attract yellowjackets, not paper wasps. Because they contain attractants, they can often attract more from surrounding areas than you might have originally had. Traps are most effective in the spring when the queens (only) are out – catching them will prevent their future offspring.

Yes, they will immediately attempt to build new nests – they are trying to survive! The lifespan of these insects is only a few weeks, so they will continue so there are queens to provide young next spring. Only the queens will survive the winter – all of the others will die, and egg production will cease when there is not enough time to rear them to adults.

Remember that these nests may not be confined to the community garden. The open areas around the garden, the landscaping around the medical facility, and agriculture areas are also nest sites. Like honeybees, these insects forage and nest long distances. Eliminating the nests inside the garden will help, since nest disturbance is one cause for aggression, but it’s not the only cause for aggression.

The predatory wasps are not social wasps, so they don’t have a nest to defend. They are solitary insects that lay their individual egg in a hole in the ground, a stem of a plant, or in the living body of their “host” insect. Sometimes they build mud cells or use small empty cavities. When they lay that egg, they also put a living insect in with it to feed on while it grows into an adult. That individual cell is sealed, and they move on to do another. There are many different kinds of these wasps, with different nest sites. Solitary wasps rarely come in contact with us, and even more rarely sting. Most of these do not look anything like the yellowjackets or paper wasps, so they will not be easily confused. They also vary in size and color.

Native bees are normally non-aggressive. Honeybees are the same, as you know. However, colonized honeybees are not all from the same brood stock, and some can be more aggressive than others. It’s important to correctly identify the stinging culprit.

I’m sending along some reading material. These have been published by CSU, so are research-based and pertinent to our area. The first is our fact sheet on nuisance bees and wasps, and the second is a link to a PowerPoint presentation given to an incoming group of new beekeepers to teach them about these fascinating insects. The presentation is long, and the first half is about honeybees. However, the last part is about wasps, and he’s very good at summarizing the important points about them. The last two are more fact sheets providing more details on the two most likely culprits.

• Nuisance Colorado Bees and Wasps: https://extension.colostate.edu/docs/pubs/insect/05525.pdf
• Colorado Bees and Wasps: Bees & Wasps: A Review of Colorado Species (colostate.edu)
• Yellowjackets: Colorado Insect of Interest (colostate.edu)
• European Paper Wasp: European Paper Wasp - 5.611 - Extension (colostate.edu)
• Insect information menu (see the listing for many other insects) – see the section on hymenoptera, which is the group that includes bees and wasps: Arthropods of Colorado - Agricultural Biology (colostate.edu)

Karin