Ground Nesting Bees

Ground Nesting Bee Classification
Class: Insecta
Order: Hymenoptera
Family: Apidae
Genus: Halictidae, Ptilothrix, Colletes, Andrenidae, Megachilidae
Species: There are 16 known species of Ptilothrix, over 500 known species of Colletes, more than 630 known species of Megachilidae, while the species and subspecies of Halictidae and Andrenidae both number in the thousands

The ground nesting bee is a non-honey-producing bee that is native to North America. With thousands of ground nesting bee species across the globe, this variety is considered the biggest contributor to crucial vegetation pollination. 

Many entomologists believe ground bees are on the verge of extinction, due to the more alluring production of honey and the explosion of managed honeybee hives. 

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    What are Ground Nesting Bees?

    Most ground nesting bees belong to one of four scientific families Colletidae, Andrenidae, Megachilidae, and Halictidae. The latter of these four species is the most common numbering greater than 4,300 subspecies worldwide.

    The earliest ground nesting bees evolved over 130 million years ago and are assumed to be have been of a solitary species. [1][2][3]

    Ground nesting bees do not exist in a cohesive colony unit with one queen, like the common honeybee.[4] Rather, the ground nesting bee will nest underground or in cavities with single female bees solely caring for their own brood in a dedicated tunnel. Only the female bee and developing young inhabit this tunnel.

    Some ground nesting bees, like the bumblebee, are not solitary bees and have large colonies with a single queen. 

    Due to their social construct, social ground nesting bee cavities must be much larger than a solitary bee nest to accommodate movement and operations.[5] Bees that belong to the ground-nesting category are commonly known as a membrane or cellophane bees, digger bees, sweat bees, squash bees, and mason bees.[6]  

    When considering the topic of ground nesting bees, the majority of bee enthusiasts will think of the bumblebee. However, more than 70% of the worldwide population of bees are ground nesting, totalling more than 20,000 different subspecies. 

    Understandably, within this huge number of ground nesting bee subspecies we find many different behavioural and social structures.[7]

    Where Do Ground Nesting Bees Live?

    The nesting bee Colletes species have been logged in many areas of North, Central, and South Americas, all across Europe, Eastern Asia, Russia, and the Northwestern and Southeastern regions of Africa.

    In contrast, the smaller nesting bee species category of Ptilothrix has only been discovered in the Southeastern regions of both the United States and South America.

    Each nesting bee species has a preferred soil type, such as well-drained, silty, hard-packed soil, clay-rich dirt, or sandy soil.[8] Scientists are unsure why a particular nesting bee species will prefer a soil type but believe it is related to their adaptations over time.

    Female ground nesters of the alkali bee will dig with their mandibles and push soil with their abdomens. The Touchet Valley, US holds a large population of the alkali bee which have been documented to move as much as 96 tons of soil (collectively) in a year.[9]

    Ground nesting bee emerging from ground nest
    Despite great variation in nesting soil types, ground nesting bees tend to prefer patches with good drainage and southern exposure.

    Female ground nesting bees can build one or several nests in different locations over a lifetime, and most will never even meet their offspring. Some species of ground nesting bees can produce more than one generation per year. 

    Ground bees born within the winter or other cold periods often complete their development in the nest, spending winter in a hibernation state, waiting for the more favorable conditions of spring before emerging.[10]

    The alfalfa leafcutter and the alkali bee are ground nesting bees native to particularly arid regions in the western US. In contrast a species of small, colorful, ground nesting bee known as the orchid bee lives in a tropical or subtropical climate in the northern region of Mexico down to Argentina. [11]

    How to Identify Ground Nesting Bees?

    There are various ways to identify a ground nesting bee, size being one, they generally range in size from one-half inch to three-quarter inch. Another ground nesting bee characteristic is colour which is as diverse as size, but common colors are black, blue, green copper, or metallic red.[12]

    Male ground nesting bees are usually distinguished by their long antennae and lack of a stinger. For most ground-nesting bees or solitary bees, only the female will have a stinger for protecting her young. 

    The ground nesting bee species Ptilothrix bombiformis (hibiscus bee or eastern digger bee) have a fuzzy light yellow or cream-colored thorax and a wide black abdomen. Compared to the Colletes inaequalis (plasterer bee), which has a much darker-haired thorax, with a thinner, longer abdomen that appears striped.

    What Kind of Bees Make Nests in the Ground?

    Bees that make nests in the ground are predominantly Mining Bees (Andrena sp), Polyester Bees (Colletes spp), Digger Bees (Anthora spp), Sweat Bee (Halictus spp), and Long-Horned Bees (Melissodes spp).

    Most ground nesting bees will tunnel their nests in warm patches of bare or sparsely grassed ground of varying soil types. However, other ground nesting bees will seek out abandoned beetle burrows or the trunk of a dead tree or fallen branch.

    For example, mason bees often build nests using mud or plant fiber chewed into a paste; leafcutter bees will create a cocoon-like form out of leaves, sand, and resin, while a carder bee usually harvests plant fibers similar to leafcutters.

    Other ground nesting bees will construct mud partitions between brood cells or tunnels produced in soil. Some also use hollowed out plant stems, branch or rock cropping cavities, or even empty snail shells or the abandoned tunnels of other insects for their nests.[13]

    The majority of ground nesting bees, which is the same as saying most bees in general, are solitary, meaning they do not work in unison under one queen like a colony. 

    However, there are a few ground-nesting exceptions like the sweat bees (alkali bees), and bumblebees that are are considered social, existing in colonies with a single queen, worker bee females, and male drones.

    For your safety, don’t confuse a gentle solitary/ground nesting bee with ground-nesting yellow jackets or wasps (Vespidae). 

    Female solitary/ground nesting bees will construct individual tunnels for her young, each with its own surface access opening. This will look like one bee flying in and out of many tunnel openings. 

    Wasps, or ground-nesting yellowjackets, are social colony builders filled with hundreds of wasps that will typically only use a single opening as both entrance and exit to their nest. This will look like multiple bees flying in and out of one opening. 

    Solitary/ground nesting bees are generally understood to be docile, while yellowjackets are not. Yellowjackets have a well-documented propensity to protect and will readily attack with a painful sting, sometimes more than once.[14]

    Common ground-nesting bee comparison:

    Mining bee Andrena sp measuring 1/4-1/2 inch Polyester bee colletes app measuring 1/2-3/4 inch Digger bee anther spp measuring less than 3/4 inch Sweat Bee Halictus spp Two long-horned bees melissodes spp measuring 1/2-3/4 inch
    Mining Bee Andrena sp ¼-½ inch Polyester Bee Colletes spp ½-¾ inch Digger Bee Anthora spp Less than ¾ inch Sweat Bee Halictus spp ¼-½ inch Long-Horned Bee Melissodes spp ½-¾ inch

    How to Identify a Ground Nesting Bee Nest?

    When identifying a ground nesting bee nest you may see one or many cone-shaped mounds of dirt with an opening at the top, which serves as the entry point.[15]

    Ground nesting bees generally prefer nesting in areas with early sun exposure and semi-dry or well-drained soils that are light on organic matter. Tunnels are usually dug in areas of sparse vegetation, and damp soils are avoided due to the possibility of flooding.

    If the soil and environmental nesting conditions are favorable, there may even be hundreds of solitary/ground nesting bee nests in close proximity. Scientists have documented some female species to share an entrance but dig in different directions for their brood tunnels. 

    Different ground nesting bee species nest in various soil types but generally favor patches with southern exposure and good drainage.[16]

    Ground nesting bee nests will sometimes be shallow, only a few inches deep, while some can extend to nearly 10 feet deep.

    In the case of the leafcutter bees, they will line their nests with small half-eaten semicircles of leaves that have been glued together (more commonly found in discovered holes or cavities and not directly in the ground). 

    After completing their nests, female ground nesting bees will fill it with the nectar and pollen mixture and proceed to lay eggs within.

    Do Ground Nesting Bees Sting?

    Scientists have been able to conclude that solitary/ground nesting bees are largely docile, gentle, and productive pollinators.

    Ground nesting bees are primarily non-aggressive, and only the females are able to sting when handled roughly, at the cost of their life.[17]

    Most humans have an aversion to bees due to a reputation for the few that sting but these are more likely to be wasps, not solitary, pollinating, ground nesting bees, which are often as small as a grain of rice and unable to sting a human or cause much harm if they did. 

    Solitary/ground nesting bees die after deploying their stingers, and if a mother bee dies before her young have been fully nourished, her offspring will also die. Male solitary bees cannot sting at all and really only serve to mate and marginally aid in pollination.[18]

    Do Ground Nesting Bees Pollinate?

    Solitary/ground nesting bees do pollinate and are often regarded as Earth’s champions of pollination. Ground nesting bees will fly plant to plant, collecting loose pollen on their legs and body fur.

    Once collected, ground nesting bees then deposit pollen into the “baskets” on their legs, with pollen collected solely as food source for their brood.

    Mason bees are critical pollinators in our world as they’re fast fliers that can visit a large number of flowers. This ground nesting bee tends to be most active in early spring and doesn’t let poor weather deter their collection, making them ideal pollinators for early blooming plants and fruit bearing trees such as apple trees.[19]

    Did you know that ground nesting bees do not intentionally pollinate? The pollination process occurs when bees forage and loose pollen attaches to their bodies.

    Squash bees (found in the U.S. often together in large numbers[20]) specialize in pollinating squash, gourds, and other similar plants. Scientists have determined that these curb-nesting pollination specialists can actually outperform the common honey bee. However, we’re yet to discover a way for this ground nesting bee to be managed or cultivated.

    Another ground nesting bee, the bumblebee is also a very effective pollinator, especially for tomatoes, and is often managed by year-round greenhouses. All they require is a queen, a nest (usually not underground in managed colonies), and a supply of sugar water to supplement the lack of nectar in tomato plants. 

    Managed bumblebees are free-range fliers, and their pollination capabilities are a key component in greenhouse agriculture.

    Do Ground Nesting Bees Make Honey?

    Ground nesting bees have no queen to answer to and no shared resource production and therefore do not make honey.[21] Because of their solitary nature most ground nesting bees only harvest what pollen they need to nourish their own young. 

    Unlike the honeybee, ground nesting bees tend to stick fairly close to home and only take what pollen they need. Honeybees can collect pollen for miles and hoard their honey into a stockpile. 

    If these two species are nearby, the ground nesting bees may find it difficult to collect enough pollen to successfully reproduce. 

    Due to the increase of honey production and large-scale managed honeybee hives, there’s a scarcity of the more productive pollinators (ground nesting bees) as they yield little that is resourceful for humans. 

    However, it is becoming more widely understood that without these pollination champions, vegetation will be endangered.

    How to Get Rid of Ground Nesting Bees

    macro shot of ground-nesting bee's head

    Ground nesting bees tend to create their tunnels in areas of sparse vegetation and are viewed as an annoyance in expertly manicured lawns. If a yard is impacted by these solitary/ground nesting pollinators, homeowners may be in need of damage control. 

    These valuable ground nesting bees are a vital component of Earth’s ecosystem, so establishing a healthier, thicker grass bed is the appropriate cure for homeowners and the ecosystem alike.[22] 

    Recommended natural control methods include heavy watering or strategic lawn sprinkler placement during the nest-building period. Tilling soil to destroy ground nesting bee tunnels may help, but this could only be a temporary solution.

    That said, leaving the ground nesting bees to their own devices is best, and your garden will reap the rewards of their excellent pollination!

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