ID GUIDE TO WILD BEES
OF THE NATIONAL BUTTERFLY CENTER
Mission, Texas

Osmia subfasciata mason bee - (c) Copyright 2019 PaulaSharp

MASON BEES  &  RESIN BEES

Tribe Osmiini:  Osmia & Heriades

OSMIA MASON BEES

Associated plants: 

 

Retama
(Parkinsonia aculeata)

Honey mesquite

(Propsopis glandulosa)
Family: Fabaceae

Creosote bush
(Larrea tridentata)
Family:  Zygophylaceae

Cowpen daisy

(Verbesina encelioides)
Family:  Asteraceae

Texas Prickly Pear
(Opuntia engelmannii)

Plant Family:  Cactaceae

These bees use cactus for
building materials; they feed
on a wide array of flowers.

When seen:  

March 2018, March 2019,
February 2020 

Osmia subfasciata Mason Bee

Osmia (Diceratosmia) subfasciata

Family:  Megachilidae

Size:   8 mm  (female)

           7 mm (male)

Bees of the species Osmia subfasciata are a striking iridescent blue-green, a trait shared by other members of the subgenus Diceratosmia

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A female Osmia subfasciata mason bee on a prickly pear cactus nopal (leaf-pad). As noted in this guide page's introduction, this bee was biting off materialis from a prickly pear plant to transport to its nest.

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These are leaf buds on the edges of a spring prickly pear. Each bud is protected by prickles and exudes an orange frothy liquid that appears to attract O. subfasciata mason bees.

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An O. subfasciata mason bee leaning back to investigate a cactus pad

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Female bee

A male Osmia subfasciata mason bee: males have dense white hair on their faces.

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A male Osmia subfasciata mason bee from above

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Male bees have bands of white hairs on the top surfaces of their abdominal segments

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The male bee's sternum (underside of the abdomen) is metallic blue-gren and lacks scopal hairs (unlike the female bee's).

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Male bee

Osmia subfasciata mason bee on prickly pear - (c) Copyright 2019 Paula Sharp

An iridescent blue-green female Osmia subfasciata mason bee 

Osmia subfasciata mason bee on prickly pear - (c) Copyright 2019 Paula Sharp

A female Osmia subfasciata mason bee on prickly pear

Osmia subfasciata mason bee; Copyright (c) 2020 Paula Sharp

A male Osmia subfasciata

Osmia subfasciata mason bee; Copyright (c) 2020 Paula Sharp

A male Osmia subfasciata

Steel-blue Mason Bee

Osmia (Helicosmia) chalybea
 

Family:  Megachilidae

Size:   12-15 mm  (female)

          10-11 mm (male)

Associated  plant at NBC:  

Texas thistle

Circium texanum
(Family Asteraceae)

When found:

April 2021

A female steel-blue mason bee

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A female bee on a Texas thistle

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Vertex of female bee

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A male steel-blue mason bee

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Vertex of male bee

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A female Osmia chalybea

A female steel-blue mason bee; Osmia chalybea; Copyright 2021 Paula Sharp

A female Osmia chalybea

A male steel-blue mason bee; Osmia chalybea; Copyright 2021 Paula Sharp

A male Osmia chalybea

MASON BEES
Genus Osmia

Mason Bees and Texas Prickly Pear Cactus

Both Osmia mason bees and the Heriades resin bees shown further below on this page belong to the bee tribe Osmiini.  Female bees of this tribe carry pollen on scopal hairs located under their abdomens, rather than on their back legs.  In this way, they resemble the leafcutter and wood-borer bees shown on the previous pages of this guide.  

The name "mason" derives from Osmia bees' practice of utilizing plant parts and soil to construct nests.  Mason bees employ materials such as masticated leaves, resin, mud and even pebbles to engage in  "masonry".  The  bees build partitions separating their nests' egg chambers; construct walls to seal nest entrances; and occasionally line walls with transported materials.  Mason bees often nest in hollowed-out pithy stems or in pre-existing holes and cavities found in wood or, less often, in soil or rock cavities. 

In the Lower Rio Grande Valley of Texas, mason-bee activity may entail the novel practice of using the succulent flesh surrounding the stickers of prickly pear cactus as building material.  The bee shown at right was observed in late March, 2019, harvesting pieces of the soft, newly-emerged buds of a spring prickly pear cactus growing at the National Butterfly Center.

The bee was one of many iridescent blue mason bees engaging in this activity:  over the period of a few days, this website's authors observed numerous mason bees visiting the same prickly pear and then using their jaws to carry mouthfuls of cactus to a wooded area where the bees disappeared into tunnels leading inside a rotted log. 

 

Afterwards, we examined various prickly pear plants throughout the county of Hidalgo and encountered other groups of the same industrious blue bees using Texas prickly pear (Opuntia engelmannii) to build their nests.  In all cases, the bees seemed to do no damage to the cactus:  they focused on collecting soft materials gathered around the spines protruding from newly budding nopales (cactus pads).  

The blue mason bee species observed on prickly pear and shown here has been identified as Osmia subfasciata by Texas bee expert Dr. Jack Neff, President of the Central Texas Melittological Institute and author of a vast compendium of publications on bees, among them  "Nest biology of Osmia (Diceratosmia) subfasciata Cresson in central Texas (Hymenoptera: Megachilidae)".

According to this article, Osmia subfasciata mason bees are polylectic -- that is, they forage on a wide gamut of plants.  They are solitary, like most members of their genus.  Osmia subfasciata build their nests in beetle burrows; abandoned snail shells; plant stems; and abandoned wasp nests.  The bees fashion mortar from chewed-up plant parts mixed with coarse sand or soil. 

 

Osmia subfasciata mason bees transport balls of masticated plant material to a nesting area, drop each ball onto the ground and then chew and knead it while rolling it along the ground to incorporate sand or dirt into the mass.  The bees use this cement mixture to construct the walls and partitions of their nests.  The viscous flesh of prickly pear cactus may well provide a good glue base for a natural cement.

Although several females may collect materials from the same cactus, Osmia subfasciata mason bees are not gregarious; they do not build their nests close together to form nest aggregations like some solitary bees.  Each female O. subfasciata bee independently constructs and provisions her own nest, arranging her egg chambers in linear series along a tunnel-hole, and laying around twelve or fewer eggs.  When utilitiling snail shells as nest cavities, the female bee deposits a single egg in a shell, provisions it with food and then encloses it within protective materials.

After hatching, Osmia subfasciata bee larvae pupate for as long as ninety days.  In Texas, they emerge in August and then overwinter as adults.  In the Lower Rio Grande Valley, adults re-emerge in late March to recommence the species life cycle.

 

Mason Bees' Importance as Pollinators

Mason bees are essential pollinators of crops, wildflowers and woodland, grassland and desert plants.  There are many varieties of mason bee within the state of Texas -- among them are Osmia ribifloris, an important pollinator of blueberries; Osmia georgica  and O. texana, which pollinate strawberries, caneberries and melons, as well as an array of wildflowers and garden flowers; and Osmia chalybea, a thistle specialist.  In many parts of the United States, mason bees are bought and sold commercially for use as pollinators in apple, cherry and other fruit orchards.

Physical Characteristics of Mason Bees

Mason bees belong to the tribe Osmiini of the family Megachilidae. Female mason bees carry pollen on scopal hairs located on the undersides of their abdomens, a trait that helps identify them -- and which they share with other members of the Megachilidae family, such as leafcutter, resin and carder bees.  The scopae (pollen-carrying hairs) of mason bees may be white, yellowish, dark brown, black or -- like those shown on the Georgian mason bee shown at right -- electric orange.  Mason bees sometimes have orange hairs on their lower faces as well, as sported by the Osmia chalybea  shown at right and further below on this page.

Osmia mason bees are small-to-medium-sized, with robust builds and relatively large heads.  The color and size of mason bees vary significantly by subgenus.  Bees of the subgenera Diceratosmia and Helicosmia, for example, are usually metallic green or blue.  Their bodies are partly covered with pale hairs and their abdomens may be banded with stripes of pale hair as well.  Mason bees of the subgenus Melanosmia tend to have more robust builds and very dark green or black coloring, while the subgenus Osmia includes two imported species with a markedly different appearance: the hornfaced bee and the bull mason bee, which are large, covered with dull brown hairs and endowed with brightly-covered scopal hairs.

Mason bees possess other distinctive characteristics of the tribe Osmiini:  their forewings have only two submarginal cells (as opposed to the more usual three), and their front feet sport an extra part called an arolium. These traits, which aid greatly in identifying mason bees, are illustrated in the photo strip at right.

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A blue mason bee exploring a Texas prickly pear cactus  (Opuntia engelmannii)

The tender buds of newly-sprouting pads on a prickly pear cactus

A female Osmia subfasciata mason bee investigates a prickly pear bud.

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The bee fastens its jaws onto the prickly pear bud

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The bee pulls off a piece of the cactus.

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The bee transports the plant material to its nest.

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An Osmia fasciata mason bee biting off part of a prickly pear.

Osmia georgica Mason Bee - (c) 2016 Copyright 2015 Sharp-Eatman Photo

An Osmia georgica mason bee with bright orange scopal hairs under its abdomen

Osmia chalybea mason bee - (c) Copyright 2019 Paua Sharp

An Osmia chalybea mason bee

All female mason bees have pollen-collecting hairs called scopae, located on the undersides of their abdomens. This Osmia georgica mason bee's scopal hairs are bright yellow-orange. On mason bees generally, scopal hairs may be white, pale yellow, light-brown or black.

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Mason bees have an extra part on each front foot, called an arolium. The arolium is a pad located between the toe-like tarsal claws of the front foot. This is a trait common to members of the tribe Osmini, which helps distinguish them from other small members of the family Megachilidae. The brown mason bee shown here is a member of the subgenus Osmia.

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Members of the bee tribe Osmini have only two submarginal cells on each forewing. Most native bees of the United States have three marginal cells in their forewings.

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TAXONOMY OF OSMIA MASON BEES 

Order:   Hymenoptera

Family:   Megachilidae

Subfamily:   Megachilinae

Tribe:  Osmiini

Genus:  Osmia

Species shown on this page:  
    Osmia (Diceratosmia) subfasciata
    Osmia (Helicosmia) chalybea

A female steel-blue mason bee; Osmia chalybea; Copyright 2021 Paula Sharp

Osmia Mason Bee Species of the National Butterfly Center

HERIADES RESIN BEES

RESIN BEES
Genus Heriades

Heriades bees are referred to in some texts as “mason bees” and in others as “resin bees”.  These native bees nest in pre-existing holes in wood and hollow stems, and they use plant resin to plug entrances to their egg chambers.  Heriades bees are specially equipped with mandibles designed to scrape resin from plants.

Heriades bees of several subgenera are found throughout the world, but a single subgenus, Neotrypetes, occurs within North America, ranging from Canada to Panama.  

Approximately 10 Heriades species inhabit the United States, at least 7 of which are found in Texas.  

The common name "resin bee" is also applied to other bee genera – for example, resin bees of the leafcutter genus Megachile are shown on this guide’s leafcutter bee page.  Heriades bees are significantly smaller than resin bees of that genus.  The variegated Heriades resin bees shown here, for example,  are a mere 5-6 mm (less than 1/4 inch) in length. 

Physical Characteristics of Heriades Resin Bees

Like the Osmia mason bee shown above, Heriades resin bees belong to the tribe Osmiini of the family Megachilidae.  Thus, as noted, the females carry pollen on scopal hairs under their abdomens; and the bees' forewings have only two submarginal cells.

 

According to entomologist Charles D. Michener, defining traits of bees of the genus Heriades include the following:  (1) A ridge runs across the front top edge of the first segment of the bee's abdomen (as shown in the photo strip at right); and (2) the front face of the bee's abdomen is concave.

Heriades resin bees found in the United States are black with pale hair bands.  Coarse Indentations pit their heads, thoraxes and abdomens.  The under-abdomen scopal hairs on which females carry pollen are usually white and often long and conspicuous even to the naked eye, despite the bees' small size. 

Male Heriades bees lack scopal hairs, but males can be recognized by their abdomens, which curl under, the tips nearly touching the front segments.  On males, only S1 and S2, the first two sterna (bottom surfaces of the abdominal segments) are generally visible. Viewed from above, the last segment of the male bee's abdomen (T7) is hidden by the sixth segment (T6), which is untoothed and not notched.  These features are illustrated in the entry below.

 

Heriades females of various species are differentiated by minute traits such as the appearance of ridges and protuberances on their jaws, and the density and size of the pits on their upper abdominal segments.  Males are told apart by equally minute attributes, such as the  sculpting and pitting of the sterna (the undersides of the  abdomen); and the length of the  vertex (the distance between the small eyes called ocelli and the back of the bee's  head).

Pollinator Plants

Heriades resin bees tend to be generalist pollinators that forage on a range of plants.  The variegated resin bee featured below on this guide page was found foraging on the  weed known as Spanish needles (Bidens alba).  This Heriades  species has been documented feeding on an array of plants, such as thistles, mallows, sunflowers, melons and members of the pea family.

Heriadies variolosa resin bee - (c) Copyright 2019 Paula Sharp

A female variegated Heriades resin bee

The heads and bodies of Heriades resin bees are heavily pitted.

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Female Heriades resin bees of the United States tend to have pale stripes on their abdomens and pale pollen-collecting scopal hairs on their abdomens.

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The top front edge of the first segment of a female Heriades resin bee's abdomen is ridged.

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TAXONOMY OF HERIADES RESIN BEES 

Order:   Hymenoptera

Family:   Megachilidae

Subfamily:   Megachilinae

Tribe:  Osmiini

Genus:  Heriades

Subgenus:   Neotypetes

Species shown on this page:  
    Heriades (Neotrypetes) variolosa
     
(Variegated Heriades resin bee)

Heriades Resin Bee Species of the National Butterfly Center

Variegated Heriades Resin Bee

Heriades (Neotrypetes) variolosa
 

Family: Megachilidae

Size: 7 mm  (female)

          5 mm (male)

Associated  plant at NBC:  

Spanish needles

Bidens alba
(Family Asteraceae)

When found:

October 2019

A female variegated Heriades resin bee

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A dorsal view of the female bee: note the heavily-pitted head and thorax.

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Scopal hairs of female bee

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A male Heriades variolosa

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Dorsal view of bee: note the coarse pitting on the bee's head and thorax, and the way each segment of the abdomen bells outward, a trait of all Heriades bees

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Close-up of abdomen of male bee: the way the abdomen curls under, hiding its seventh segment (T7), is a distinguishing trait of males bees of the genus Heriades. So is the concave front face of the first segment (T1) of the abdomen.

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Heriadies variolosa resin bee - (c) Copyright 2019 Paula Sharp

A female variegated Heriades resin bee

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A male variegated Heriades resin bee:  the curled-under abdomen is characteristic of Heriades bees.