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

MASON BEES  &  RESIN BEES

Tribe Osmini:  Osmia & Heriades

MASON BEES
Genus Osmia

Mason Bees and Texas Prickly Pear Cactus

Both Osmis mason bees and the Heriades resin bees shown further below on this page belong to the bee tribe Osmini.  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 at right 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 Osmini 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 also shown at right.

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 Osmini:  their forewings have only two submarginal cells (as opposed to the more usual three), and their front feet sport an extra part called an areolum. These traits, which aid greatly in identifying mason bees, are illustrated in the photo strip at right.

Osmia subfasciata mason bee - (c) Copyright 2019 PaulaSharp

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

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

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

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

TAXONOMY OF OSMIA MASON BEES 

Order:   Hymenoptera

Family:   Megachilidae

Subfamily:   Megachilinae

Tribe:  Osmini

Genus:  Osmia

Subgenus:   Diceratosmia

Species shown on this page:  
    Osmia (Diceratosmia) subfasciata

Associated plant at NBC: 
 

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  

Osmia subfasciata Mason Bee

Osmia (Diceratosmia) subfasciata

Family:  Megachilidae

Size:  12 mm  (female)

An iridescent blue-green female Osmia subfasciata mason bee 

Detailed Photographs: 

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

A female Osmia subfasciata mason bee on prickly pear

Osmia Mason Bee Species of the National Butterfly Center

RESIN BEES
Genus Heriades

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

 

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

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

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

Physical Characteristics of Resin Bees

Like the Osmia mason bee shown above, Heriades resin bees belong to the tribe Osmini of the family Megachilidae.  Thus, as noted, the females carry pollen on scopal hairs under their abdomens; the bees' forewings have only two submarginal cells; and their front feet sport an extra part called an areolum. 

Heriades resin bees are black with pale hair bands and conspicuous indentations pitting 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.   Males lack scopal hairs, but often can be recognized by their abdomens, which curl upward, the tips nearly touching the front segments. 

 

Female Heriades like the variegated Heriades resin bee shown on this guide page 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 shapes and pitting on the undersides of their front abdominal segments; 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 in this guide was found foraging on the exotic weed known as Spanish needles (Bidens alba).  This 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

TAXONOMY OF HERIADES RESIN BEES 

Order:   Hymenoptera

Family:   Megachilidae

Subfamily:   Megachilinae

Tribe:  Osmini

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:  Halictidae

Size: 7 mm  (female)

Associated  plant at NBC:  

Spanish needles

Bidens alba
(Family Asteraceae)

When found:

October 2019

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

A female variegated Heriades resin bee

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

A female variegated Heriades resin bee

Permissions and Copyright Information:   All images on this site are (c) Copyright 2018-2019 Paula Sharp and Ross Eatman.  All rights reserved. All photographs are protected by registered copyright.  Please contact Sharp-Eatman Nature Photography for written permission before using any of these images for any purpose. 

Last updated November 2019

 1-15-19