Summer Bees, Wasps, and Other Pollinators

Summer in Southern Oregon starts when the rain stops. In the beginning it is mild, warm, and generally pleasant. In recent times the pleasant warm days in the start of summer give way to smoke and excessive heat. Wildfires in the region seem to be the new normal, and the smoke typically lingers for months until the first autumn rains.

A mating pair of European wool carder bees.

Pollinator activity seems to be reduced in the smoky mid and late summer, but does not cease completely. For many bees and wasps summer is not just the only time they are active in the year, but also the time that they seek and find mates. Unlike honey bee queens which do not visit flowers and mate high in the air, most solitary bees and wasps mate among plants and flowers. Males often stick around a particular area that they have made their own territory, and some species fiercely defend this territory from other males by chasing and grappling with other males. This behavior is particularly noticeable among male carpenter bees (Xylocopa spp.) and wool carder bees (Anthidium spp., pictured mating above).

Megachile rotundata visiting a basil flower

Leafcutter bees (Megachile spp.) and related bees (family Megachilidae) are a common sight in summer. They are distinguished from other families by possessing scopae (specialized pollen collecting hairs) on the underside of their abdomens rather on their legs like most bees. Of course, females are the only ones which have scopae since males don't collect pollen or provision nests. In spring this year I released 40 alfalfa leafcutter bees (M. rotundata) in my garden to observe them. Unfortunately, few took a liking to the nesting materials I offered, and their cocoons were under constant attack from ants and earwigs. The ones that survived had a marked liking for the basil I had planted.

Megachile sp.

Many other species of leafcutters live in Southern Oregon, though only one (M. rotundata) is reared intentionally and used for commercial pollination. Due to their characteristic pollen collection method, often passing their abdominal scopae over pollen laden anthers, they usually have a preference for flowers that have exerted anthers, such as many daisy type flowers in the Asteraceae.

Megachile perihirta

Most Megachile nest in tunnels in wood or woody stems, though some nest in the ground. The common name, leafcutter, is a hint at how they create their nests: by lining and partitioning cells with leaf fragments they have chewed from surrounding plants. Leaf matter is adhered together with saliva. Some, I have found, nest in mere crevices since the leaf bits form cell walls that are strong enough to deter some nest parasites.

A leafcutter bee and a paper wasp are seemingly oblivious to each other as they feed on nectar from narrowleaf milkweed

A yellowjacket on elegant tarweed foraging for budworms

Wasps are another familiar sight in the summer. While many wasps are active in spring, colonies of social wasps are more conspicuous since by this time they have grown to large sizes and now forage frequently for food for their developing brood. I was watching a yellowjacket hop from flower to flower one morning, thinking she was foraging for nectar. While many wasps do visit flowers for the sugary food, this one was foraging for caterpillars feeding on the flowers. Like honey bees, yellowjackets remember where to look for favorable foods, and this one had learned to search the tarweed flowers for her bounty.

Aphid wasp (Pemphredoninae) and aphids

This summer I grew a few large evening primrose plants. Aphids seemed to be highly interested in these large plants, and attracted many other interesting insects. Ants fed on the sugary frass, the honeydew, while syrphid flies and ladybugs deposited eggs which hatched out to become aphid eating larvae. My favorite aphid predators were the aphid wasps. These crabronids captured hundreds of aphids per day to provision their nest cells and feed their young.

Sand wasp (Bembix sp.) burrowing into her sandy nest

Another summer favorite, the sand wasps, were a joy to observe. These wasps nest near water on sandy banks. Their nests are in burrows hidden by the loose sand. Each time a female enters or exits her nest, the entrance disappears behind her. They enter their nests by digging furiously with specialized bristles on their front legs. They prey primarily on flies, and provision each individual cell with dozens of paralyzed flies.

Philanthus gibbosus

I am always happy to see the beewolves, genus Philanthus. Sandy riverbanks are a great place to spot them, as they seem to prefer loose sandy soils for their nests. I have encountered two species, P. gibbosus and P. crabroniformis. Markings on the thorax and the color of the eyes can aid in differentiating the two, with the latter having green eyes and the former (pictured) with black eyes.

Philanthus gibbosus on Melilotus alba

Beewolf is a common name referring specifically to the European beewolf (P. triangulum) but freely used to describe all species in the genus. As the name suggests, they prey nearly entirely on their close cousins, bees. American species prey mostly on solitary bees (usually Halictidae) but will occasionally prey on honey bee workers or sometimes even other wasps or (rarely) flies. Unlike many other wasps, their prey is killed, not paralyzed, before being deposited in their nest. Some species feed their young progressively, meaning the mother wasp brings prey to her developing larvae.

Thread waisted wasp nectaring on narrowleaf milkweed

If you love watching pollinators as I do, watching wild milkweeds in bloom never disappoint. Bees, flies, and butterflies are always usual visitors on milkweed flowers, but wasps are the visitors I look for most. Thread waisted wasps (Ammophila spp.) are common flower visitors, but in my experience they are wary of my presence and make observation a challenge. Not this time. This large thread waisted wasp was completely oblivious to me as I took photos. Upon close inspection of the photos, I became aware of the dozen or so pollinia attached to this wasps feet and palps. Milkweeds, like orchids, shed pollen as sticky packets. These sticky pouches containing potentially hundreds of individual pollen grains are then delivered by the wasp to a receptive stamen of another flower.

Ammophila sp.

Thread waisted wasps are kind of a treat for me, and I rarely see more than one at a time. On a hike up Southern Oregon's Mount McLoughlin in April this year (2018) I was fortunate to witness one thread waisted wasp excavating a nest in the sand of the subalpine zone. The wasp first removed the pebble she had placed over the entrance then proceeded to excavate sand particles and deposit them away from the entrance. I didn't witness the completion of the nest, but they normally finish by placing a pebble over the entrance and concealing it with sand (or soil) and nearby debris to disguise it from nest parasites.

Pompilid wasp on wild carrot

Spider wasps are some of my favorite wasps. I've probably said that about every wasp by now, and I've never lied. Spider wasps, family Pompilidae, are special. Have you ever heard the phrase nature is metal? (If you don't know what it means, google it.) Well, pompilid wasps are metal. The commonality among spider wasps is that they all use spiders as hosts for their young. Many, but not all, paralyze the spider before depositing an egg. Some deposit the paralyzed spider in a burrow with an egg adhered on its underside. The larva, once hatched, will feed on the living spider until it is ready to pupate. The largest of these wasps are the tarantula hawks, named for their choice of host. Another commonality worthy of note is that most pompilids have species specific host spiders.

Pompilid wasp on wild carrot

Pompilid wasps also have a habit of flicking their wings rhythmically, possibly seeking attention from possible predators as a warning that they could sting. While the large tarantula hawk wasps are known for their incredibly painful stings, many pompilids are small and readily flee rather than stinging. For most the sting is probably reserved for their spider host. The Pompilidae is a very diverse family when discussing biology and behavior, as they run the gamut from predator and kleptoparasite to parasitoid, depending on the species.

Ichneumon wasp

The true parasitic wasps are differentiated from the bees and stinging wasps by their lack of a stinger. The sting evolved from an egg-laying apparatus called the ovipositor. Parasitic wasps use their ovipositor to lay eggs on or within a host, usually an insect larvae. In the case of ichneumon wasps, the host is usually a caterpillar or less often beetle or sawfly larvae. Ichneumonid larvae develop within the host until pupating and emerging as a fully formed adult. The host is usually dead or dying by the time the wasp is pupating.

Chalcidoid wasp on dodder

Chalcidoid wasps are not closely related to the ichneumonoids, but they exhibit similar parasitism in some cases. They are a diverse and large group, with behavior ranging from gall formers to kleptoparasites. They are also often very small.

A honey bee and bumble bee visiting Phacelia tanacetifolia

And now back to the bees. I wanted to cover wasps first to illustrate the diversity among this group called the Hymenoptera, the order which encompasses bees, wasps, ants, and sawflies. Bees evolved from wasps millions of years ago. Plants coevolved with pollen adapted for insect distribution. To attract bees, many bee-pollinated plants evolved pollen with relatively high levels of proteins compared to pollen from wind-pollinated plants. There are a few species of bees which don't collect or eat pollen as a protein source (Trigona spp., not found in the US) and a few stinging wasps which do collect pollen as a protein source (Masarinae, vouchered in Oregon though I've not yet encountered them).

Long-horned bee on Madia elegans

Most bees native to the US live solitary lives and don't make honey. Long-horned bees are related to honey bees, but rather than living in a colony nest in congregations of underground tunnels. Each female creates her own tunnel and provisions her own brood chambers. Most solitary ground nesting bees, like most solitary bees in general, create a ball of pollen with a small amount of nectar to hold it together, lay an egg on it, and seal the chamber. Most never interact with their offspring (like many solitary wasps) and only live for a matter of weeks.

Cuckoo bee, Sphecodes

Some of the most peculiar bees in Oregon are the cuckoo bees. They don't collect pollen or make nests. Instead, females seek out nests of other types of solitary bees and lay their eggs in the host brood chambers. The cuckoo larvae kills or starves the host larvae, then develops normally to adulthood. I view cuckoo bees as a sign of a healthy host population of bees.

Ceratina on a wild Campanula

Small carpenter bees are very numerous in my area. They collect very little pollen on their bodies, collecting it instead in their crop and regurgitating it once back to the nest. Nests are built in dried pithy stems of woody plants, linear, with partitions built from the chewed pith.

Ceratina on knapweed

Ceratina visit a wide range of plants in a wide range of families. Their small size allows them to climb deep inside flowers with nectar that is inaccessible to larger bees.

Halictus on chamomile

The Halictidae, sometimes called sweat bees, are some of the most common bees in summer in some areas. They have bushy scopae, specialized pollen collecting hairs, and a notch at the tip of their abdomen (a good diagnostic feature).

Augochlora on cutleaf blackberry

Metallic green bees of the Halictidae are a special treat for the photographer.

Masked bee, Hylaeus, on wild carrot

Like Ceratina, masked bees collect pollen inside a crop and regurgitate it in the nest. These are very small bees and are often found visiting flowers in abundance in the summer, but their small size means they are probably overlooked most of the time.

Large carpenter bees, Xylocopa, on evening primrose

Some of the largest bees in the US, and my garden, are the large carpenter bees. They are in the minority of bees which excavate tunnels in wood to create their nests. They seem to prefer dead wood, such as the planks of my fence, and unpainted decks and siding of homes around the country. These large, docile bees visit a wide variety of plants over a long season. They rear two to three generation a year in my yard. Occasionally females overwinter in their nests and interact with their offspring, but I suspect this is the exception rather than the rule. Due to their ability to generate their own warmth by vibrating their flight muscles isometrically they can fly later in the day. In the middle of summer they were flying long after the sun fell to forage on the evening primrose (primarily night blooming).

A white-lined sphinx moth, highly attracted to the highly perfumed evening primrose