Pollinator Post 8/18/26
This picture was taken in mid-April this year. Things have not changed much at this wind-swept spot on the north shore of Bay Farm – the same shrubs are here, the Coyote Brush (Baccharis pilularis), Coffeeberry (Frangula californica), and the Fennel (Foeniculum vulgare). I return regularly to check on them as they are insect magnets.
Fruits are ripening on the Coffeeberry, Frangula californica.
Hey, there are still live aphids on the fruit! The tiny, dark green aphids are Melon Aphids, Aphis gossypii (family Aphididae). The bloated straw-colored aphid mummy is the same species, albeit it has been parasitized by an Aphid Mummy Wasp.
Melon Aphids, Aphis gossypii, also known as cotton aphids, are tiny (1.0-1.5 mm long), destructive pests that feed on the undersides of leaves. Ranging from light green to nearly black, they suck vital plant fluids, cause severe leaf curling, secrete sticky “honeydew” that leads to black sooty mold, and act as active vectors for plant viruses. Capable of cloning themselves, a single female produces dozens of live young, allowing populations to mature and reproduce in as little as 5-7 days. Winged females are produced for dispersal when the colony is overcrowded or when resources dwindle. Natural predators include lady beetles, lacewings, and parasitic wasps.
Aphid Mummy Wasps, Aphidius sp. (family Braconidae) are small wasps, typically less than 1/8 in. long. The female wasp lays a single egg in an aphid. When the egg hatches, the wasp larva feeds inside the aphid. As the larva matures the aphid is killed and becomes bloated and mummified, usually turning tan or golden in color. The adult wasp chews its way out of the mummy leaving a circular hole.
The Coyote Brush is blooming profusely. I can easily spend the rest of my hour here observing the insects that are attracted to the tiny flowers. Let the pollen party begin!
This Coyote Brush is a male plant. Tiny male flowers appear in tight clusters, with protruding stamens offering abundant pollen.
Just by sticking her tongue into the inflorescences for nectar, the Honey Bee’s face and body are covered with the sticky pollen.
Asteraceae pollen features abundant sticky pollenkitt on its spiny outer surface. Pollenkitt is composed of lipids, carotenoid and flavonoid pigments, proteins, and carbohydrates. The sticky coat holds scents and visual cues that attract bees and other insects. Pollenkitt sticks pollen grains to the bodies of insect pollinators and clumps them together, preventing loss during transport. The pollenkitt also helps anchor the pollen grains to the plant stigma after delivery. In contrast, wind-pollinated plants usually have little to no pollenkitt so their pollen remains dry and light.
That Honey Bee, Apis mellifera (family Apidae) is an over-achiever. Look at the size of her pollen load!
The pollen collecting apparatus in Apidae bees, which include honey bees and bumble bees, is commonly called a “pollen basket” or corbicula. This region is located on the tibia of the hind legs and consists of hairs surrounding a concave region. After the bee visits a flower, she begins to groom herself and brushes the pollen down toward her hind legs and packs the pollen into her pollen basket. A little nectar mixed with the pollen keeps it all together like putty, and the stiff hairs surrounding the pollen basket hold it in place. Remarkably bees are able to fly while carrying up to a third of their body weight in pollen.
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After foraging on flowers, the Honey Bees often back off into the air, hovering in mid-air to clean their faces and to pack the pollen neatly into the pollen baskets using her legs.
I just read about an interesting study on bee nutrition. Bees obtain nearly all of their food from flower nectar and pollen. Nectar supplies mostly sugar, while pollen is their primary source of protein. However, pollen did not evolve mainly as a food reward for pollinators. It is the male reproductive material of plants so its nutritional composition does not necessarily provide bees with the ideal mixture of nutrients needed for growth, survival and reproduction. Honey bees appear to have a way of dealing with the nutritional limitations of pollen, especially when feeding their developing larvae.
Worker honey bees gather pollen from a wide variety of flowers and store it inside the hive as ‘bee bread’. Nurse bees eat this material and process its nutrients into glandular secretions, including royal jelly, which are then fed to developing larvae. In a study, researchers found that bee bread contained a more balanced essential amino acid profile than most individual pollen sources. Royal jelly provided an even closer match to the amino acid composition of bee tissues. The results suggest that combining pollen from different plants and then processing it through nurse bees may allow honey bee colonies to compensate for the nutritional shortcomings of individual pollen sources.
This nutritional system is not available to every bee species. Many wild bees, including bumble bees and solitary bees, provide pollen directly to their offspring. In habitats with only a small variety of flowering plants, these bees may have difficulty obtaining the appropriate balance of essential amino acids for both themselves and their developing young. The results of the study suggest that planting for pollinators should not only focus on providing flowers throughout the season, but also on ensuring a diversity of pollen sources. A varied diet may be essential for bees to obtain the right balance of nutrients.
I wonder how oligolectic and monolectic bees manage to balance the diets of their offspring? Perhaps they have co-evolved with their limited host plants to such an extent that their nutritional needs are completely matched by what the plants provide?
A large Bristle Fly, Archytas marmoratus (family Tachinidae) has landed on a cluster of Coyote Brush flowers.
The family Tachinidae is by far the largest and most important group of parasitoid flies. All species are parasitic in the larval stage. Most adults have distinct abdominal bristles, hence the common name. Adults feed on liquids such as nectar and honeydew. They can be found resting on foliage, feeding at flowers or searching for hosts.
Most Tachinids attack caterpillars, adult and larval beetles, true bugs, grasshoppers, and other insects. Females lay eggs in or on the host. Tachinid larvae live as internal parasites, consuming their hosts’ less essential tissues first and not finishing off the vital organs until they are ready to pupate. The larvae leave the host and pupate on the ground. Tachinids are very important in natural control of many pests, and many have been used in biological control programs.
Archytas marmoratus is a species of Bristle Fly in the family Tachinidae. The flies feature a distinct “marbled” pattern on their abdomen. The species is found primarily in the Americas. Females lay microscopic maggots (planidia) on or near the larvae of moths, particularly the fall army worm (Spodoptera frugiperda) and Corn Earworm (Helicoverpa zea). The maggots penetrate the host, develop internally, and eventually emerge from the host’s pupa as adult flies. As a natural parasitoid, it is frequently used in biological control of target agricultural pests.
A Soldier Fly, Odontomyia sp. (family Stratiomyidae) is resting on the flower buds of Coyote Brush. The body of the fly is very flat (dorso-ventrally compressed) and its folded wings do not fully cover the sides of its abdomen.
Members of the genus Odontomyia occur throughout much of the world, found in woodlands, fields, usually near water. They are 9-12 mm in length. Adults take nectar, also sometimes found on dung. When not in flight, Soldier Flies (family Stratiomyidae) tend to hold their wings neatly folded, one above the other over the abdomen, not quite covering the width of their abdomen. Larvae are aquatic and feed on algae. Eggs are laid on the edge of body of water. Larvae stick the tip of their abdomen through the water surface to obtain air.
Too many stripes – even the eyes are striped! The hover fly has gone overboard with its wasp mimicry. To me, the Interrupted Hornet Fly, Spilomyia interrupta (family Syrphidae) is the joker of the Syrphid world, compulsively swinging of its wings from side to side. It teases us by mimicking a yellowjacket, and yet gives itself away by this odd behavior.
In classic Batesian mimicry, many Syrphid flies mimic Hymenoptera (bees and wasps) species. The mimicry provides a measure of protection from predators for these harmless flies. Spilomyia is a remarkable mimic of Vespid species including Yellowjacket wasps. They mimic Yellowjackets both physically as well as behaviorally. The yellow-and-black outfit is only a start. The anterior portion of the forewings of Spilomyia are a darker brown than the rest of the wings, reminiscent of the Yellowjackets that fold their wings longitudinally at rest. The fly has a habit of resting on their back four legs and moving their two front black legs above their head, mimicking the way common wasps move their antennae. When threatened, the fly is able to produce a buzz in a frequency similar to some hymenopteran species. What’s more, Spilomyia is active during the same time of year as its model wasp, and frequently visits the same plants.
The Interrupted Hornet Fly, Spilomyia interrupta is an uncommon hover fly species native to western North America, particularly the California coast. Adults are often seen on flowers seeking nectar and pollen during the warmer months, June to October. The adult’s eyes are rather unusual, having vertical black stripes and speckling. Larvae are described as ’short-tailed’ and adapted for aquatic or semi-aquatic conditions in tree rot holes where they feed on decaying organic matter.
A large fly with iridescent bronze abdomen and spotted eyes has landed on the flowers of Coyote Brush to clean itself of pollen. It is easily recognizable as the Common Lagoon Fly, Eristalinus aeneus (family Syrphidae).
The Common Lagoon Fly, Eristalinus aeneus (family Syrphidae) is a widespread species, native to Europe and found throughout the United States. Its common name derives from its habitat, which includes lagoons, ponds, and slow-moving streams. Key features are the small, dark spots on its eyes, which tend to merge at the top. The adult flies are pollinators, feeding on nectar and pollen from flowers. The larvae are found in damp environments, often with decaying seaweed. They are also known as “rat-tailed maggots”, for the long siphon on their rear end that acts like a snorkel, helping them breathe under water. The larvae are saprophagous, feeding on bacteria in water rich in decomposing organic matter.
Why those spotted eyes?
This is the answer a Google search yields: The pigment spots and bands in the eyes of the Common Lagoon Fly and related hover flies create optical filtering across different parts of the compound eye’s ommatidia (lens units). The patterning aids in judging distances and tracking tiny shifts in light and shadow, which is vital for maintaining a near-motionless hover in mid-air. Sharp visual acuity allows the fly to target flowers accurately while competing with other pollinators.
The spots in the fly’s eyes remind me of the frits on car windshields. Might not the physics be the same? This is what I learned:
– the frits protect against UV radiation
– control heat absorption and dissipation across the surface, distributing the thermal load more evenly
– prevent optical distortions known as lensing effects, preventing localized overheating
– scatter the passage of sunlight, preventing the creation of of focal points that could lead to dangerous temperature spikes
For the Lagoon Flies that live in wide open sunny habitats close to water and its reflective glare, all the above properties of the frits can be beneficial.
A Common European Greenbottle Fly is foraging on the flowers of Coyote Brush.
The Common European Greenbottle Fly, Lucilia sericata (family Calliphoridae) is a Blowfly found in most areas of the world and is the most well-known of the numerous green bottle fly species. The lifecycle of Lucilia sericata is typical of blowflies. Females lay masses of eggs in fresh carrion. The flies are extremely prolific – a single female may produce 2,000 to 3,000 eggs in her lifetime. The larvae feed on dead or necrotic tissue, passing through 3 larval instars. Third-instar larvae drop off the host to pupate in the soil. The adults feed opportunistically on nectar, pollen, feces, or carrion; they are important pollinators as well as important agents of decomposition. Pollen is used as an alternative protein source, especially for gravid females who need large amounts of protein and cannot reliably find carrion.
While we may find the blowflies disgusting for their association with filth and carrion, they are important decomposers/ recyclers in the ecosystem. What’s more, their larvae are used in maggot therapy to clean wounds by consuming only dead and infected tissue, helping to promote faster healing and prevent infection.
Scattered pollen grains have adhered to the hairs of this furry Cellophane Bee, Colletes sp. (family Colletidae), giving its fur coat a slight yellow tinge.
The bee family Colletidae includes generalists and specialists, and they are likely important pollinators of many wildflowers. All Colletidae in North America are solitary ground nesters, but some species nest in large aggregations. There are two major genera of Colletidae in North America: the Masked Bees (genus Hylaeus) and Cellophane Bees (genus Colletes). The most obvious shared characteristics of Colletidae is also the hardest to see: their short tongue. Colletes are moderately hairy, slender bees, ranging in size from 7 to 16 mm. Distinct features include a hairy head and thorax, pale bands of hair on the abdomen, and a heart-shaped head. The eyes of Colletes are angled (rather than being parallel), making the face slightly heart-shaped. The eyes of Colletes are angled (rather than being parallel), making the face slightly heart-shaped.
The genus name Colletes means “one who glues”, referring to their habit of applying a glue- or cellophane-like lining to the walls of nest cells, using their specialized tongues. This lining gives rise to their common names: cellophane bees, polyester bees, and plasterer bees. Colletes tongue is unique: short, flat, and forked at the tip. Colletes line their nests with a distinctive cellophane-like substance made from saliva and secretions from the Dufour’s gland on the abdomen. Using their specialized tongue, they paint the walls with saliva, then with secretions from the Dufour’s gland, they add a coat of varnish. This creates a clear covering that is strong, durable, and resistant to mold and water.
Uh oh, the Cellophane Bees better beware – a brood parasite is among them! In fact this cuckoo bee might have grown up as their nest mate. iNaturalist has confirmed that it is a Least Cellophane-cuckoo Bee, Epeolus minimus (family Apidae).
The term cuckoo bee refers to a variety of different bee lineages which have evolved the kleptoparasitic behavior of laying their eggs in the nests of other bees, similar to the behavior of cuckoo birds. Female cuckoo bees lack pollen-collecting structures and do not construct their own nests. Cuckoo bees typically enter the nests of pollen-collecting species, and lay their eggs in cells provisioned by the host bee. When the cuckoo bee larva hatches, it consumes the provision in the nest, and kills the host larva. Many cuckoo bees are closely related to their hosts, and may bear similarities in appearance reflecting this relationship. Others parasitize bees in families different from their own.
Epeolus is a genus of cuckoo bees in the family Apidae. They are often known as variegated cuckoo bees. The species is uncommon to rare, and has strong patterns of black and white on the thorax and abdomen. These patterns are made of tiny flattened hairs lying flush with the integument or “skin”of the bee. These tiny hairs form striking, velvety black-and-white or yellowish patterns on their thorax and abdomen. All known species of Epeolus are kleptoparasites of ground-nesting Cellophane Bees of the genus Colletes. The female enters the nest excavated by the host and lays an egg in an unsealed cell. The Epeolus larva then consumes the egg of the host bee and then feeds on the pollen the Colletes bee provisioned the cell with for her offspring. Colletes bees line their nest cells with a cellophane like covering which they exude from the Dufour’s gland to protect the cell from moisture and fungal infection. Female Epeolus bees have spines on the end of their abdomens which they use to pierce U-shaped holes in this covering so that she can oviposit between its layers; she also secretes a small amount of glue to attach her egg to the cell.
Epeolus minimus is among the most widespread Epeolus species in North America.
I spot something small and slender on the flowers of Fennel, Foeniculum vulgare. On closer inspection, the insect reveals itself to be a Spotted Beewolf, Philanthus multimaculatus (family Crabronidae). These wasps are inordinately fun to photograph!
Beewolves (genus Philanthus) are solitary, predatory wasps, most of which prey on bees, hence their common name. The adult females dig tunnels in the ground for nesting, while the territorial males mark twigs and other objects with pheromones to claim the territory from competing males. As with all other spheroid wasps, the larvae are carnivorous, forcing the inseminated females to hunt for bees on which she lays her eggs, supplying the larvae with paralyzed prey when they emerge. To prevent fungal growth on the stored prey, female Philanthus wasps secrete symbiotic bacteria from specialized antennal glands. Some Philanthus species specialize on certain bee species, others may be generalists that prey on a wide variety of bees. The adults visit flowers for nectar. The best known beewolf is the species that prey on honey bees.