Pollinator Post 7/23/26 (1)
It’s time for me to visit Crab Cove in Alameda again. The season has gone by so fast I wonder what plants are still in bloom in the park.
St. Catherine’s Lace, Eriogonum giganteum is blooming profusely near the visitor center. Most of the insect visitors are the American Sand Wasps, Bembix americana (family Crabronidae).
Sand wasps in the genus Bembix are familiar and common throughout North America, digging their burrows in dunes, on beaches, and other habitats with loose, deep sand. The female rapidly kicks out large quantities of sand using a “tarsal rake” of spines on each front leg. The burrow is excavated before the wasp goes hunting. Bembix are generalist, opportunistic hunters. True flies in the order Diptera are the usual prey. A victim is paralyzed or killed by the wasp’s sting, and is then flown back to the nest. Most species will lay an egg on the first victim, while some species lay an egg in the empty cell before starting to hunt. Once the egg hatches, mama wasp brings flies to her larva as needed. This “progressive provisioning” is rare in the insect world. When the larva reaches maturity, mama wasp closes the cell. Inside, the larva spins an oblong cocoon, weaving sand grains into the structure and resulting in a hardened capsule. Overwintering takes place as a prepupa inside this cocoon, but there are usually two generations a year.
Male sand wasps often engage in an elaborate flight ritual called “sun dances”. Males emerge before females, and fly erratically at dizzying speed one or two inches above the ground attempting to detect virgin females about to emerge from their underground nests. Both sexes are often seen taking nectar at flowers, especially from Asteraceae family. Bembix wasps are often victims of other insects such as cuckoo wasps (Chrysididae), velvet ants (Mutillidae), satellite flies (Sarcophagidae), bee flies (Bombyliidae), and thick-headed flies (Conopidae).
A Yellow-faced Bumble Bee, subgenus Pyrobombus (genus Bombus, family Apidae) is foraging on the flowers of St. Catherine’s Lace. She is carrying light yellow pollen on her pollen baskets (corbiculae).
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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I walk barefoot along the short stretch of beach at Crab Cove, watching young children play in the shallows.
European Searocket, Cackile maritima is blooming beautifully on the sandy beach. A Honey Bee, Apis mellifera (family Apidae) is reaching into a flower for nectar. Wow, check out the pollen load on her hind leg! Like the bumble bee we saw earlier, Honey Bees carry pollen in their corbiculae or pollen baskets.
Those are the characteristic wavy black-and-white bands on the abdomen of an American Sand Wasp. These wasps visit flowers for nectar to fuel their own energy needs while they hunt living flies to feed their growing larvae.
A Sandhill Skipper, Polites sabuleti is taking nectar from the flowers of European Searocket.
Skippers are a family, the Hesperiidae, of the order Lepidoptera (butterflies and moths). They are named for their quick, darting flight habits. Most have the antenna clubs hooked backwards like a crochet hook. They also have generally stockier bodies and larger compound eyes than the other butterflies. Their wings are usually small in proportion to their bodies. When at rest, skippers keep their wings usually angled upwards or spread out, and only rarely fold them up completely. Californian species are mostly brown or tan, with black, orange, or yellow markings.
Skipper caterpillars are usually green or brown, sometimes yellowish, never brightly colored. They have a distinctive “collar”, a narrow ring around the body right behind the head. Caterpillars are camouflaged and often hide during the day. Many species make nests of leaves and silk for additional protection. Most North American species feed on grasses, but some common species eat shrubs and trees, especially in the bean family. Most species are limited to a single group of food plants. Adult skippers are only active during the day, but Skipper caterpillars feed mainly when it is dark or partly light.
The Sandhill Skipper, Polites sabuleti is a small, variable butterfly found in Western North America. They frequently inhabit grasslands, lawns, and alkaline meadows, where they feed on nectar and rely on saltgrass (Distichlis) as a larval host.
A Beach Fly (family Canacidae) is perched on a searocket flower. It is difficult to photograph these flies because of their minute size as well as their pruinescence.
The Beach Flies (family Canacidae) are minute (1.6-5 mm) yellow, gray or gray-brown pruinose flies with whitish to grayish markings. The head is large with small antenna bearing bare to pubescent arista. The “mouth” is a large oval opening. The Canacidae are found along the sea coasts, on the surface of small bodies of water, saline and fresh, in places protected from the wind. They feed on infusoria and other tiny organisms. Infusoria is a word used to describe various freshwater microorganisms, including ciliates, copepods, euglenoids, planktonic crustaceans, protozoa, unicellular algae and small invertebrates.
Pruinescence or pruinosity on an insect is caused by a powdery or waxy “bloom” secreted by the insect’s body that sits on top of its hard outer shell (cuticle). This waxy layer masks the underlying coloration, giving the insect a dusty, frosted, or “hoarfrost” appearance. The waxy coating can serve several functions: it can reflect sunlight and ultraviolet (UV) radiation, helping the insect avoid overheating in hot, sunny environments. The wax is also highly water-repellent (hydrophobic), which prevents the insect from losing moisture and protects against desiccation. In some insects the reflected UV light from waxy coating can serve as a vibrant visual signal for mate recognition, species identification and territorial threat displays.
Where the slope breaks on the upper beach, the bank is pocked with many holes. This is where the consolidated sand provides ideal nesting sites for sand wasps and other ground-nesting insects.
An American Sand Wasp, Bembix americana (family Crabronidae) is entering its burrow entrance.
An American Sand Wasp is excavating a burrow on loose sand. Note the characteristic position of her front legs as she digs – curled inward. The action is best seen on video: An American Sand Wasp is digging a nest burrow on a sandy beach. – YouTube
Female American Sand Wasps feature specialized tarsal rakes – combs made of stiff spines on the outer edges of their front legs – that let them rapidly scoop and kick sand backward to excavate underground nest burrows. The wasp often moves both front legs simultaneously to fling sand backward like a frantic dog.
This pale pink buckwheat is blooming beautifully in the native plant garden in the park.
The American Sand Wasps, Bembix americana (family Crabronidae) dominates the floral scene here as well. The sandy coastline of Alameda provides ideal habitats for these wasps.
An inchworm caterpillar of a Pug Moth, Eupithecia sp. (family Geometridae) is feeding on an inflorescence of Redflower Buckwheat.
Inchworms are also called loopers and measuring worms. The majority of the inchworms are the larvae of moths in the family Geometridae. The name comes from the Greek “geo” for earth and “metro” from measure, because the caterpillars seem to be measuring the surface on which they are walking. The “looping” locomotion is mandated by the absence of prolegs in the middle section of the caterpillar’s body.
Eupithecia is the largest genus of moths of the family Geometridae. Occurring worldwide except for Australasia, species in the genus are commonly known as pugs. The caterpillars move in a looping manner and are commonly called inchworms. Adults are typically small, 12 – 35 mm, with muted colors. Most species rest with forewings held flat at right angles to the body, while the hindwing are largely covered by the forewings. They are generally nocturnal. Larvae mostly feed from the flowers and seeds of their food plants rather than the foliage. Many species have a very specific food plant. Many are commonly found on Asteraceae flowers.
A small black bee is crawling out of a Sticky Monkeyflower, Diplacus aurantiacus. Even before it is fully out in the sunlight, I can see the yellow markings on its face. It is a female Masked Bee, Hylaeus sp. (family Colletidae). She must have gone to the base of the flower for nectar.
The Masked Bee has yellow markings in various places on her body as well. Note that she has no scopa on her hind legs, like most other bees. That’s because she does not carry pollen on any external structures on the body. She transports pollen and nectar that she has collected in her crop, part of her digestive system.
The bee turns around and reaches up to collect pollen from the anthers hidden behind the white, two-lobed stigma above her.
Hylaeus (family Colletidae) are shiny, slender, hairless, and superficially wasp-like bees. They are small, 5 to 7 mm long, usually black with bright yellow or white markings on their face and legs. These markings are more pronounced on the males. Hylaeus do not carry pollen and nectar externally, they instead store their food in the crop and regurgitate it upon returning to their nests. They are primarily generalist foragers. Hylaeus are short-tongued, but their small body size enables them to access deep flowers. Hylaeus nest in stems and twigs, lining their brood cells with self-secreted cellophane-like material. They lack strong mandibles and other adaptations for digging, using instead pre-existing cavities made by other insects.
The Masked Bee climbs up onto the stamens to collect pollen.
After a while she crawls out on the upper petal as if ready to fly away, but then decides to return to the anthers again.
There are only a few fresh flowers left on the Sticky Monkeyflower, or any of the plants close by. I can understand why the bee is reluctant to leave a precious resource given such scarcity.
Hey, there’s another bee coming out of an adjacent Sticky Monkeyflower. It is larger and more stocky in build, jet black and glossy. It is a Small Carpenter Bee, Ceratina sp. (family Apidae).
The Small Carpenter Bee genus Ceratina is closely related to the more familiar, and much larger Carpenter Bees (genus Xylocopa). Ceratina are typically dark, shiny, even metallic bees, with fairly sparse body hairs and a weak scopa on the hind leg. The shield-shaped abdomen comes to a point at the tip. Some species have yellow markings, often on the face.
Females excavate nests with their mandibles in the pith of broken or burned plant twigs and stems. While many species are solitary, a number are subsocial. Both male and female carpenter bees overwinter as adults within their old nest tunnels, emerging in the spring to mate. In the spring, this resting place (hibernaculum) is modified into a brood nest by further excavation. The female collects pollen and nectar, places this mixture (called bee bread) inside the cavity, lays an egg on the provision, and then caps off the cell with chewed plant material. Several cells are constructed end to end in each plant stem.
Besides the Masked Bees and Small Carpenter Bees, Diplacus aurantiacus is also pollinated by bumble bees (Bombus) and mason bees (Osmia). The tubular, nectar-rich flowers are also a favorite of hummingbirds.