Solitary Bees

Written On: by Theo The Beekeeper

You might have seen many bees buzzing about in the flowerbeds of your garden or flying low on the ground. These cute tiny insects are often not the typical honeybee but are one of nature’s best pollinators. These are the precious solitary bees!

Solitary bees are not part of a colony and do not make honey. The male fertilizes the female, who builds a nest to house her eggs, collects nectar and pollen to sustain her brood, and is an excellent pollinator. Males and females have short lifecycles and don’t live to see their young become adults.

The solitary female bee plays a crucial part as a pollinator of crops, plants, and flowers as she forages for pollen and nectar to feed herself and provide for her future offspring.  Read on for more facts about the life cycle, habitat, and fascinating world of the different types of solitary bees!

Solitary Bees

98% of all bees in the US are solitary bees, and there are over 4 000 species native to North America.  These bees live independently and are not part of a colony with a queen and worker bees.  

The female solitary bee builds her own nest, collects her own pollen and nectar, and lays her eggs without help from her fellow bees.   

How To Recognize A Solitary Bee?

solitary bee inside of brick
wild bee Osmia cornuta looking out of insect hotel. male.

Like all bees, the solitary bee can be found anywhere in the US where flowers bloom.  They come in different sizes and shapes, build unique nests, have different seasonal activities, and visit various types of flowers.

Often these little creatures go unnoticed as they busily gather pollen.  Still, they offer a most valuable service to all kinds of flowering plants and crops. They are responsible for pollinating many plants worldwide and are a vital component in most land ecosystems.

Solitary Bees have hairy bodies, and when they are collecting pollen from a flower, pollen grains can often be seen clinging to their bodies and legs.  Some will have a pollen basket ­under their bellies for transporting this pollen.

Often you might see a solitary bee dipping into the heart of a flower; it is using its long tongue to sip the nectar.  These bees also have a second stomach or large crop for carrying the nectar.

Metamorphosis Of The Solitary Bee

The solitary bee goes through 4 stages which take 1 year to complete before it emerges as an adult bee.  These are:

The Eggs Of Solitary Bees (Stage 1)

eggs of bees inside of a hive
Close up larva wasps in wasps nest.

Depending on the species, a solitary female will lay between 20 and 30 eggs throughout her lifetime.  After mating, females will store the sperm and use it when required.  She will lay one large egg each day and seal it up with a bit of pollen. 

She makes sure her brood will survive, so she lays her eggs on top of a mound of pollen, which she has collected.   Once the eggs are hatched, usually within a few weeks, there will be food on hand for the larvae.

By using the sperm, these clever little females lay fertilized eggs at the back of the nest, which will become the next female generation.  The eggs that are not fertilized carry males and are placed at the front of the nest so that they can hatch first.  They will be the first to emerge and fly off in search of food and for a female to mate with.

The Larva Of Solitary Bees (Stage 2)

Hatching from the egg is the tiny, white worm-like larva that will feed off the pollen until it grows into a pupa.

The Pupa Of Solitary Bees (Stage 3)

The pupa usually appears during the winter months, and they already resemble the adult bee.  They are generally pale white in color and have developed legs, eyes, and wings, and are starting to grow hair on their body. 

Some species will grow a cocoon around themselves for extra protection.  These cocoons are waterproof, and diseases will have difficulty getting through.  Other species will continue to grow in the chamber they were laid in.

The Adult Solitary Bee (Stage 4)

The pupa stage is over by spring, and a young adult bee is ready to begin its solitary bee life!

Habitat Of Solitary Bees

In today’s modern world, many solitary bees are experiencing decreases in their population, resulting in a loss of pollination richness in many areas.  Factors contributing to this decline are increased pesticide use, climate change, and many of their natural habitats converted into agricultural landscapes.

Nesting For Solitary Bees

Solitary bees have particular nesting requirements, and most will build nests close to floral resources.  Some will dig tunnels in the ground and look for a favored moisture level and grain size of the soil.

Others will use mud and leaves to build nests within tree cavities on trunks and branches.  And some solitary bees chew their way into wood to make their nest.

Floral Resources For Solitary Bees

The solitary bees rely on an abundance of flowers for their daily diet.  Still, it also requires that the food is nearby.  These bees prefer not to travel more than 300m for their food, but, if need be, they will travel as far as 600m in their search. 

However, the extra time that the female needs to leave her nest for food makes her more vulnerable to predators and parasites.

Read more...  Wood Bees (Carpenter Bees + Life Cycle + Sting)

The Male Solitary Bee

two male bees going into a pipe
Osmia Cornuta, a specie of solitary bees, on a wooden nesting site.

Male solitary bees are usually smaller than females and can also function as pollinators.  You will find males usually patrolling near flowers where females visit.  They will either be defending their territory against other males or are on the lookout for a mating session. 

In this process, they gather pollen on their legs and bodies and become part of the pollination vectors.  Like all male bees, solitary male bees do not have a stinger, so they cannot sting.   They do engage in defensive behavior to protect themselves or defend their territory.  

The solitary male bee is the first to emerge from the nest in spring, and its purpose is to mate with a female to fertilize her eggs.  A solitary male bee will mate several times.  Their life span averages about 2 weeks, and after they mate, they will soon die.

The Female Solitary Bee

The female is responsible for building nest cells in which to lay her eggs and collecting pollen to feed herself and for her future offspring.  Some pollen will stick to the densely branched hairs on her hind legs.   

Or instead, she might have a crop or pollen basket to store the pollen.  A solitary female bee does have a stinger and can sting but is not known to be aggressive.  All solitary female bees are fertile and will produce eggs.  She usually only allows one male to mate with her.

Once the eggs are laid, she will seal up the nest in which pollen is also stored and leave her brood to develop independently.  Like the male, she has a short lifespan of about 6 weeks and will die shortly after laying her eggs.

Solitary Bees And Pollination

Solitary bees are effective and efficient pollinators by skimming from one flower to the next or from branch to branch in search of pollen.  As they go along their essential business, they distribute cross-pollination back and forth with every movement of their tiny bodies. 

The female will carry the pollen and nectar on the dry hairs on her hind legs or under her belly.  Some pollen will fall off and spread between the different blossoms and trees.  It is estimated that these precious little females will visit between 20 000 to 100 000 blossoms per day!  A fantastic feat for such a tiny insect.

Solitary Bees – 2 Groups

Solitary bees can be divided into 2 groups according to their nesting preferences.  They are:

Solitary Cavity Nesting Bees

These solitary bees nest primarily in underground wood cavities such as beetle burrows that have been abandoned.  The female divides the structure into several cells, and each cell will contain a single egg that will hatch into a larva.

Some female species will line the nest with leaves or floral petals foraged from nearby plants.  Species of solitary bees that nest in this way are:

Solitary Leafcutter Bees (Megachile spp.)

These solitary bees are small to medium in size (1/4 to ½ inch), and the females have black, slick striped bodies.  They build their nests in existing holes of trees, soil, and plant stems.  

The leafcutter bees will also use the shells of dead snails, holes in concrete walls (hurricane shutters), and other man-made objects for their nesting sites.  The female leafcutter bee will cut circular pieces from leaves which she will use to line her nest cavities.  She will divide the nest into cells and lay one egg in each cell.

Leafcutter bees are seen from April to October, with the peak activity in July.  These solitary bees are pollinators of legumes such as alfalfa, clover, and lupine.

It is believed that the largest bee in the world is a type of Solitary leafcutter bee (Megachile Pluto).  The females reach a length of 1.5 inches with a wingspan of 2.5 inches and are known for their enormous stag beetle-like mandibles. 

The males can grow to 0.9 inches long.  Although believed to be extinct, a live female was found and filmed in 2019 by a team of biologists in North Moluccas, Indonesia.

Solitary Mason Bees (Osmia spp.)

Mason bees are small to large (1/4 to ¾ inch) and have wide, robust bodies and heads.  Their nests are often found in beetle holes nestled in wood.  There are roughly about 150 mason bee types in North America.

The female, after mating, gathers mud in her large jaws and uses it to build a wall at the back of her nest.  This is where the name ‘mason bee’ comes from.

They can be seen from March to June, and their peak activity is in April.  Mason Bees (aka orchard bees) are exceptionally good at pollinating fruit trees, and just 250 to 300 females can pollinate an acre of apples or cherries!  

Solitary Wool Carder Bees (Anthidium spp.)

These bees are mid-sized (1/2 inch) and are known by their abdominal yellow and black stripes, resembling wasps.  The distinguishing difference is that the wool carder bee has a stockier shape and has hair on its body.  They will also be the ones carrying pollen on their underbelly.

Wool carder bees derive their name from the female who collects woolly plant hairs such as lamb’s ear to build her nest.  She will carder or scrape the hairs together to form a ball and carry them back to her nest.  The females allow multiple males to mate with her numerous times so that she can get access to the best nectar sources. 

Read more...  Black Bees (Carpenter Bees + Images + Info)

A wool carder male is very territorial and will attack other bees who come too close to his flower patch.   A male will not allow females into their flower territory unless they are potential mates.  Usually, the last male that mates with her will fertilize the eggs.

The wool carder bee is seen from May to September, and its peak activity is in July.   Their favorite forage is mint, sage, catnip, lavender, Russian sage, and hedge nettle.

Solitary Large Carpenter Bees (Xylocopa. spp)

The females of large carpenter bees are black and shiny and very large (3/4 inch).  They have short mouthparts and find it challenging to pollinate in deep trumpet-like flowers and will tear the flower’s side to get to the nectar.  These powerful mouthparts come in handy when they chew nests into the wood, hence the name carpenter bees.

Common nesting sites for carpenter bees are eaves, rafters, fascia boards, wooden shake roofs, decks, and outdoor furniture.  The female will construct her nest to house individual eggs and seal each cell with regurgitated wood pulp.  The female can live up to 2 years and will return to the same nest again the following year to lay her eggs.

The male carpenter bees, who have a golden color, seem aggressive with their loud buzz.  But they are very gentle and cannot sting.  They are merely defending their territory.  These bees can be seen from April to October, and their peak activity is in April.

Solitary Small Carpenter Bees (Ceratina spp.)

The small carpenter bees are ¼ inch in length and are shiny with dark metallic to black bodies.  They make their nests deep within semi-hollow, pre-cut, or pithy stems.

They are seen from June to September, with the peak activity in July and August.  Small carpenter bees are good at pollinating many different flowers.

Solitary Ground Nesting Bees

The females of ground-nesting bees build their nests underground and near other nests.  Many of these bees prefer specific floral resources and will make their nest close to these flowers.  These types of bees are:

Solitary Mining Bees (Family: Andrenidae)

Small to medium in size (1/4 to ½ inch), the mining bees have black or brown heads, pale hairs on the thorax, hairy face between the eyes, and there are often white stripes on the abdomen.

These bees nest underground in thin or patchy lawns.  The entrance to these nests can easily be seen by the presence of a small mud mound or turret.  They are most common in dry areas where there are only a few of their chosen varieties of flowers.

Mining bees can be seen from March to September, and their peak activity time is during April.  These bees feast on several species of orchids, including blueberry and huckleberry.

Solitary Polyester Bees (Colletes spp.)

This is a medium to large size (1/2 to ¾ inch) bee whose colors are black, brown, or grey.  Polyester bees are often mistaken for a species of mining bees.  The female digs her nest in burrows lined with waterproof secreted from her abdomen. 

She spreads the lining on the walls of the nest with her paint-brush-shaped tongue.  Hence, these bees are also known as plasterer bees.  This lining protects the eggs from drowning and the nectar and pollen from damage and spoilage. 

They come out from March to May and August to October, and their peak activity times are April and September.  Polyester bees forage and pollinate plants such as daisy, asters, carrots, parsley, and peas or legumes.

Solitary Digger Bees (Anthophora spp.)

Digger bees are large (3/4 inch) bees that are hairy.  Usually grey or shiny metallic with bold white, yellow, or rust-colored markings, their wings are much smaller than other bees.  Their nests are built by burrowing their jaws and legs into dry soil. 

You will often see them hovering low on the ground and flying very fast, but they are not aggressive toward humans and pets.   These bees will usually appear in large groupings when building their nests, but each female will have her own entrance to her nest.   Some species create a mud chimney around the entrance to their nests.

They will appear from March to October, and their peak activity will be from April to June.  Digger bees can be found in avocado or citrus orchards and near hiking trails.

Solitary Sweat Bees (Family: Halictidae)

Sweat bees are small to medium (1/4 to ½ inch) in size.  Their abdomen is solid green, red-orange, or has yellow and black stripes.  The head and thorax are often metallic green or black.  They have a strongly curved basal vein in their wing, which is different from other bees.

These bees are attracted to perspiration hence their name ‘sweat bee.’  The perspiration offers the bee much-needed salts and moisture.  The female builds her nest under the ground or in rotting wood which resembles the soil under the ground.

Sweat bees can be seen from Match to October, and their peak activity is from June to August.  These bees pollinate many wildflowers and crops such as alfalfa, sunflower, apples, and stone fruits.

Read more...  Worker Bee (Life Cycle + Images)

Solitary Long-Horned Bees (Tribe: Eucerini)

These bees are medium to large in size (1/2 to ¾ inch), hairy, are usually brown or gray with pale stripes, and have very long antennae.  The eyes of the long-horned bee are light blue or grey.

The female will dig deep tunnels in sparsely eroded soil on slopes, old walls, or cliff faces for her nest.  Although they are solitary bees, the female will sometimes share a nest entrance with other females.

They are seen from May to September, and their peak activity takes place during July and August.  Long-horned bees are pollinators for squashes, pumpkins, melons, sunflowers, and other wildflowers.

Solitary Cuckoo Bees (Nomada spp.)

Cuckoo bees are small to medium-sized (1/4 to ½ inch) and are slender and look much like wasps.  However, even in the same species, these bees can vary in size.  Some cuckoo bees have hard armor-like bodies with spines and sharp mandibles (jaws).  Their bodies are not hairy, and the females do not have a scopa or pollen-carrying structure.

Cuckoo bees are kleptoparasiting, which means they invade other female bees’ nests to lay their eggs and use that female’s brood to feed their young.   You will find the females hovering around other nests and waiting until that female leaves the nest to forage for food.  The cuckoo bee will enter the host nest, cut holes into the brood cell, and lay her eggs. 

When the egg hatch, the cuckoo bee larvae, with their strong mandibles, will attack and kill the host larvae and live off the stored pollen and nectar in the cell.  Kleptoparasitism is natural behavior with bees and is not a threat to the overall solitary bee population.

Cuckoo bees can be seen from April to August, and their peak activity is during April and May.  The cuckoo bee will only visit flowers to feed on the nectar for energy.

Securing Solitary Bees For The Next Generations

Ensuring that these amazing little bees will still be around for the next generations to know and learn about is important.  But these solitary and native wild bees must be looked after to be able to continue pollinating our crops, orchards, and wildflowers.

Conservationists often focus on setting aside special pieces of natural land for bees, but this is not enough.  We need to include bees in our agricultural lands, city parks, and yards to enable them to continue their most important job on our planet as pollinators.

How Can Humans Support Solitary Bees?

Should you live in either rural or urban settings, here are some ways you can help support and conserve solitary bees.

  • Think carefully before using pesticides and chemical fertilizers.  It is not always necessary and is toxic to bees.
  • Create natural gardens with flowers native to the area and which will be favored by the area’s native solitary bees.  Choose flowers with many petals to provide pollen and nectar for the foraging bees
  • Choose yellow and blue flowers, which are attractive colors for bees, and strong and heavy floral scented flowers will have lots of pollen and nectar.
  • Ensure that the garden will have flowers all year long for the different species of solitary bees.
  • Allow your garden to be a bit messy by providing grasses and trees in which solitary female bees can build their nests
  • Leaving a woodpile or a stack of leaves in a corner will be good for some bees to nest in.  If you prefer a neater garden, then rake up the leaves, but hide some behind trees and shrubs for the little bees.
  • Fill a pie plate with water and keep it in the garden for bees and insects to take a drink.  Place a layer of stones in the dish so that the bees can perch on them and won’t drown when taking a drink of water.
  • Involve urban planners in setting up pollinator-friendly roadside plants and doing native landscaping in parks and recreational spaces.
  • Build bee houses for solitary mason bees to nest in.  Use natural materials such as paper, reeds, or wood to create tubes and place these inside a container to build a house for the female to lay her eggs.  The nests need to remain dry, so be sure the housing will protect the tubes from the rain.

Conclusion

Solitary bees are not part of a social hive; they do not make honey and do not have a queen.  Instead, the sole purpose of the male bee is to mate with females to fertilize her eggs.  A solitary female bee, after mating, will build her own nest and forage for food for the larvae to develop into the next generation of solitary bees.  The solitary female bee is an excellent pollinator.  In her short 6-week life cycle, she will pollinate many flowers, plants, fruit trees, and agricultural crops.  The solitary bee is an integral part of the world’s ecosystems and should be given all the help and support from humans to ensure they will still be around for many generations.

Author

Theo The Beekeeper

When I was a kid, my dad used to keep bees around the small farm we had, and I absolutely loved helping him. In the past few years, we’ve picked up the hobby again, and I’ve been doing a lot more research. This website is the accumulation of things I’ve learned along the way! You can learn more about my journey and the resources I’ve developed on my about page.

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