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

Pollinators and Wildflowers of Mount McLoughlin

Mount McLoughlin is one of the most stunning and recognizable natural landmarks in the Rogue Valley. With an elevation of 9,493ft it is the sixth highest mountain in Oregon. It is a volcano, and the entire mountain is littered with volcanic rocks. The mountain is located between Medford and Klamath Falls in the Sky Lakes Wilderness. But all that aside, I have looked on at Mount McLoughlin with wonder. I wondered, what is up there? What is it like to be on that mountain? I'm not an experienced hiker, but I had to do this.

Dicentra formosa (Fumariaceae) in the subalpine zone in June

I made four separate treks on the mountain, but only made it to the summit on the most recent hike. My first climb was August 2017. My decision to experience the mountain was a spur of the moment choice. I started on the trail later than was needed to make the summit and descend before darkness fell, so I descended before summiting. My second attempt was in November 2017, one day after another hike which I had achieved a minor injury. The cold and my injury were too much, so I gave up early on the trail.

A view from the ridge, high winds and clouds enveloped the top of the mountain.

June this year I was back on the mountain. Little was in bloom, and it was fairly cold. I had arduously reached the ridge, but dark clouds were moving in around the mountain from the East. Thunder was rumbling from the distance. Before I knew what was happening, the storm was right overhead. Snow and lightening prompted me to make a swift descent! In my slightly panicked haste, I lost the trail several times on the way down through the subalpine zone (dominated by many large basalt fragments, dwarf trees, and a poorly discernable trail). It was not ideal.

Wasp-mimic syrphid fly (Chrysotoxum) eating pollen on Lilium pardalinum

I encountered much more pleasant weather on the mountain this July. Driving up to the trailhead on a pitted rocky dirt road, I passed by so many wildflowers in bloom! It was exactly what I needed to boost my spirits and give me the optimism I needed to reach the summit, finally.

Pacific coralroot orchid (Corallorhiza mertensiana; Orchidaceae)

Gleefully on my way up the trail, eyes mostly to the ground, I spotted a delightfully intriguing plant! Of course I encountered many interesting plants, but one that stood out among the rest was the parasitic coralroot. Instead of photosynthesizing, these orchids get all they need from relationships with ectomycorrhizal fungi. The fungi gets what it needs to live from relationships with the roots of surrounding conifers.

Pompilid wasps

As I progressed up the trail, I noticed the characteristic wing flicking of spider wasps (Pompilidae). Four or five small pompilids were very interested in a small area on the side of the trail, maybe a few inches in diameter. Most pompilids hunt spiders to paralyze and feed to their young, but some are kleptoparasites of other pompilids. I found one such kleptoparasitic pompilid last year. I can't help but wonder if these too were kleptoparasites attracted to the hidden burrow of another pompilid.

Scree on the southern face of Mount McLoughlin

Finally, and arduously, I reached the subalpine zone. The trees are sparsely distributed, dwarfed, and contorted. Soil, if you could call it that, is highly mineral, mostly sand and fine gravel. Wildflowers were blooming everywhere in pockets between large rocks. Deep roots keep the plants anchored in the loose dry substrate. Hiking at this stage becomes challenging, and the trail is frought with many obstacles. This is when the fun begins.

Eriogonum pyrolifolium (Polygonaceae)

Life high on the mountain is hard for plants. Prolonged snow cover, harsh weather, strong wind, loose soils, a short growing season, and animal predation creates a very trying environment for high elevation plants. Most of these plants cope by having deep extensive root systems and small above ground manifestations. Many bloom very quickly as soon as weather permits to cope with the short growing season. Summer for us in the lowlands is spring on the mountain.

Pinus contorta in the subalpine zone

The trail becomes slightly harder to follow as one gets higher on the mountain. It's not that there isn't a discernable trail, but that there are many discernable trails, likely from hikers that came before you that went the wrong way. My view is that it is hard to get lost going up. All you have to do is just go up. Going off the beaten path might make the ascent more difficult, as was my case. This was partly due to my desire to A.) see more wildflowers, B.) explore my own limitations, and C.) avoid other hikers.

Bombus mixtus on Eriogonum marifolium ♀

During my hike, the most numerous wildflowers were a few species of Eriogonum, or wild buckwheats, namely E. marifolium and E. pyrolifolium. The yellow flowered E. marifolium is interesting in that it is dioecious, that is, plants are either male or female. Female phenotypes have flowers which turn red as they age, while male phenotypes have all yellow flowers with a shorter corolla. In my observations, eriogonums are visited by a wide range of pollinators.

Large pompilid wasp on Eriogonum marifolium ♂

While there were bees present on many of the mountain wildflowers, the most conspicuous floral visitors were spider wasps. Large and small pompilids were on nearly every eriogonum I encountered. In other words, sit and watch an eriogonum and within a minute there would be at least one, sometimes two, pompilids on the flowers.

Pompilid wasp visiting Eriogonum pyrolifolium

Spider wasps are some of my favorite wasps. Not only do I think their way of life is brutal and cold (AKA very cool!) but they have a beautiful form. While they are rarely brightly colored, they do attract attention by their rhythmic wing flicks and jolty movements. Some species are known to have painful stings, something I would like to explore in greater detail.

Eriogonum pyrolifolium

Eriogonum pyrolifolium has an odd common name: dirty socks. The internet claims it is a tip of the hat to their delightful smell. I haven't thought to give them a whiff. Yet. Maybe the next time I see these flowers I will remember to smell them.

Bombus vandykei queen and worker on Penstemon davidsonii

Davidson's penstemon is found in varying elevations on the mountain, normally in rock crevices. It is probably exclusively visited by bees. I have not seen any pollinator but various bees visit it on my various hikes up the mountain.

Bombus on Castilleja arachnoidea (Orobanchaceae)

Paintbrush are strange plants. They are thought to be parasitic on the roots of other plants growing nearby. Flowers are hidden within bracts that must be folded back by bees to access the nectar. Osmiine bees and bumble bees were foraging on them during my hike, and interestingly enough, it was the first time I've seen any pollinator visiting Castilleja.

Ammophila nest entrance, covered by a single pebble.

Thread waisted wasps (Ammophila; Sphecidae) are pretty awesome, and plentiful on Mount McLoughlin. They are fairly nervous creatures. Their nests, which are provisioned with paralyzed caterpillars, are constructed in sandy soils. They have the peculiar behavior of using a pebble to cover the entrance while they are looking for prey. When the nest is provisioned and eggs are laid, the entrance is covered completely by sand and debris to hide any sign of a nest to discourage parasites.

Ammophila female above her nest entrance

By a stroke of luck, I happened to be sitting and drinking some water on the scree when a thread waisted wasp alighted right next to me. She removed the pebble covering the entrance to her nest (which I hadn't noticed previously) and proceeded to continue excavation.

When thread waisted wasps are excavating their nest tunnels, the excavated sand is deposited away from the entrance of the nest so as not to draw attention to the location of the nest entrance.

Luetkea pectinata (Rosaceae)

Partridgefoot (Luetkea pectinata) is a plant that seems to grow exclusively on the south facing scree. I haven't ventured onto the northern or western slopes to determine if it grows there, too. Flies sem to have been the primary pollinators, though bumble bees were also seen on the flowers.

A view down the northeastern flank

Did I mention it was hot? It was hot. I was staying hydrated, but a pounding headache was making the already difficult trek even more difficult. I started to feel like Frodo on Mount Doom trying to deliver the One Ring to the firey pit from whence it came. At this point my entire body was jelly and I was questioning my life choices.

Hulsea nana (Asteraceae)

While eriogonums still managed to hold some ground in the alpine zone (there are no trees here), Hulsea nana was the champion of the harsh conditions of the top. The exquisite foliage alone make this plant a treat, and the bright yellow daisies were encouraging. Small flies were visiting the flowers, but I had lost the will to wait for a good photo opportunity. Onwards and upwards, keep going up! (I kept joking to myself that there were just a few vertical miles to go.)

Eriogonum pyrolifolium near the summit with... a honey bee?!

Yeah. I get within ten minutes of the summit and I see a honey bee. Why did I not see a single honey bee anywhere else on the mountain? Where did she come from?! I wonder if she was from a managed hive somewhere at the base of the mountain, or a feral colony hidden within a rock crevice or tree hollow. The mystery will haunt me until I die.

A tiny wasp lands on me once I reached the summit, Platygastridae?

I have long since unlearned the habit of immediately brushing off an insect that finds its way onto my skin. First, I look to see what it is. In this case, it was a tiny wasp! The quality of the photo is probably too poor to ever get a positive ID, but knowing that wasps are equally attracted to me as I am to them makes my heart happy.

Horntail (Urocerus; Siricidae) on the Mount McLoughlin summit

So, I made it to the summit. It was epic! There were exactly zero plants growing on the tip top, but there must have been thousands upon thousands of insects; mostly flies and horntails. Woodwasps, sawflies, and horntails are ancient phytophagous (plant feeding) progenitors of wasps. Siricid woodwasp larvae feed on decaying wood of conifers.

A view of fellow hikers on the summit, looking southeast