Colorado's Yellow Stripey Things (Stinging Insects)

Posted by: Abi Saeed, Garfield County Extension

Colorado is home to endless outdoor activities, especially in the summer months. The state is also home to an abundance of flora and fauna, including native and non-native species of some stinging insects, which can sometimes get in the way of that outdoor fun. Most of the time, a select few of these nuisance species are responsible for most stings and unpleasant encounters. However, not every yellow stripey buzzing thing is a pest, and most bees and wasps mind their own business, and go about their day collecting food and resources (seldom noticed by anyone). In fact most of these insects (including those mentioned below) are considered to be beneficial organisms that play a role in providing valuable services: bees are well-known pollinators and most wasps are important predators and parasitoids of several other arthropods, which help keep pest populations at manageable levels.

A European Paper Wasp Nest located in a Western Colorado shed:
Nests like these in high-traffic areas can lead to unpleasant interactions.
(Photo: Abi Saeed)

Here are two of the most common stinging wasps of Colorado:

1. Western Yellowjacket (Vespula pensylvanica)The Western Yellowjacket is a common, ground-nesting wasp, and can be aggressive if you are near their nest. They can be found scavenging a variety of foods, including sugary foods high in energy, dead insects / animal carcasses, and trash. They are a social wasp, meaning that they nest communally (with 100s of individuals in a strong nest) and work together to gather and protect resources. This wasp is commonly found in outdoor areas, and their nesting choices can sometimes bring them in close proximity with outdoor enthusiasts, gardeners, and picnic-goers. This insect is the most important stinging pest in the Western United States, and can be aggressive if you find yourself too close to their nest. Their nests are not readily visible, because they are underground- and Yellowjackets will abandon their nests and rebuild a new one each year.
2. European Paper Wasp (Polistes dominula)
   Similar in appearance to yellowjackets, European Paper Wasps are non-native wasps (arriving to Colorado in 2000). They create a small paper nest (made of chewed up wood fibers), and will readily utilize small spaces in which to build them (including under leaves, overhangs, and small cavities). Their nests (and colony size) will grow over the course of the summer- and larger nests can have up to 100 individuals. These are predatory social wasps, which hunt and capture other live insects to feed on. They are also an annual wasp, and will rebuild their nests every year.
   
   Aside from the above wasps, there are a few other insects that are known to sting (though, usually only when disturbed/threatened):
3. Baldfaced Hornet (Dolichovespula maculata)
   Baldfaced hornets produce a large characteristic above-ground paper-enclosed nest (usually placed in trees/shrubs and other out of the way places). Colonies of these social wasps contain 400-700 workers, and have omnivorous feeding habits. They will abandon their nest in the fall and rebuild a new nest the following year. They are a beneficial insect, playing a role as a predator of several arthropods.
4. Bumble Bees (Bombus sp.)
   Bumble bees will nest in existing cavities in the ground (such as old rodent burrows) and build a nest to start a colony. Number of bees within a nest can vary between 50-400 individuals, depending on the species. They build a new nest each year, but a new queen can find and use the same cavity to build a nest the following year. Bumble bees are vital pollinators and provide valuable ecosystem services.
5. Honey Bees (Apis mellifera)
   Honey bees, arguably the most famous stinging insect and most charismatic pollinator, are often blamed for stings that come from other insects. European honey bees are usually mild-mannered, making them a great human companion (just ask a beekeeper!). They nest in large perennial colonies, ranging from 10,000 – 50,000 (or more) individuals in a nest (usually in hives tended by humans or cavities found in nature). These bees will only sting if they perceive a threat, and can guard their hives from predators and honey-loving scavengers. Workers in a hive can only sting once, due to a barbed stinger (that will lodge itself into the victim, and remove the connected digestive system- resulting in the bee’s death). Queen bees (smooth stinger) can sting repeatedly, though they usually only use this as a weapon against other queen bees when competing for a nest. Honey bees are vital pollinators, and provide important ecosystem and agricultural services (including crop pollination across the world). 

It is important to consider the fact that: although many of these insects have the capability to sting- they provide important ecosystem services including pollination and pest control, without which our landscape would be very different from what we see today. Minimizing the proximity to their nests can play a role in reducing unpleasant interactions, and removing colonies from high-risk areas (including near playgrounds, schools, indoor structures, and patios) can sometimes be necessary.

An abandoned Baldfaced Hornet Nest, opened up to demonstrate
the inner cell structure, and external paper coverings.
These nests will be abandoned in the fall, and rebuilt in the spring.
(Photo: Abi Saeed)

To learn more about some of these nuisance wasps, and how to trap them, check out this Blog Post:
http://csuhort.blogspot.com/2019/04/springs-not-so-nice-things.html

For more information summarizing these stinging insects, check out these resources:
https://webdoc.agsci.colostate.edu/ipm/COStingingInsectsFINALgb.pdf
https://extension.colostate.edu/topic-areas/insects/nuisance-wasps-and-bees-5-525/
https://extension.colostate.edu/topic-areas/insects/european-paper-wasp-5-611/