Current Nature Report

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In a tucked-away corner of Mount Pisgah Arboretum, a small, largely intact native prairie abides alongside a trickling stream, now nearing the end of its seasonal flow. Here certain wildflower species thrive in numbers, whereas they are only found in scattered populations across the rest of the hill. Rosy plectritis (Plectritis congesta) [pictured] and Spring gold (Lomatium utriculatum) [pictured] form a dense mat of color highlighting the contours of the streambank as the ravine retreats upward into an oak woodland. To the left, as the lomatium and plectritis reach some intangible boundary, hundreds of Baby blue-eyes (Nemophila menziesii var. atomaria) amass on a western slope. Below the trail, as oak woodland resumes, Oregon saxifrage (Saxifraga oregana), Henderson’s shooting star (Dodecatheon hendersonii), and Prairie star (Lithophragma parviflorum) take hold.

 

 

As the weather continues to warm, an increasingly greater number of pollinating insects have begun flying. Of particular significance and great abundance is a peculiar bee-mimic fly. A vast number of flies mimic wasps and bees in appearance, and this particular fly, the Large bee-fly (Bombylius major) mimics our native bumblebees, most closely resembling the Mixed bumblebee (Bombus mixtus). Their bodies covered in dull-orange fur, at first glance they can be easily mistaken for a bumblebee. These bee-flies can be distinguished by their darting, hummingbird-like flight, and their extremely long proboscis and legs, which lend them an adorably cartoonish appearance.

 

 

As this bombylius descends upon a plectritis flower, its proboscis stretched out and down, its legs and face can be seen coated in pollen. It is evident that they are a significant source of pollination, especially for the plectritis, which demands the attention of a long proboscis to obtain the nectar located at the base of a long tube, as seen here. On this particular flower-head, the two lower flowers have already been pollinated and are now forming seeds.

 

This bombylius is visiting the flower of the highly invasive Shiny geranium (Geranium lucidum). Bombylius behavior is interesting to observe, as they seem to set their mind to a particular species of flower and ignore all others for some length of time.

 

This native bee (Family Megachilidae[?]) is covering its abdomen in the pollen of a Baby blue-eyes flower. Large bees are rarely seen visiting the Baby blues, but this particular bee visited several others afterward.

 

 

A better fit, this smaller native bee (Family Colletidae [?] ) was more at home on the small Nemophila flowers. A large number of this bee species was to be found exclusively pollinating the Baby blue eyes in this location.

 

This flurry of activity  has attracted the attention of a number of predators. Beautiful and well-camouflaged Flower crab spiders (Misumena vatia) lay in wait for unsuspecting prey.  This species of spider can be found on a wide variety of the flowering species at the Arboretum in mid-spring.  If you have a garden at home, you are likely to have encountered it in the past.

 

And small ones as well. While certainly a crab spider of the family Thomisidae, I am unsure if this is a young individual or an adult of a separate species. There were ants crawling over many of the flowers—perhaps this spider’s chosen prey.

 

Not all predators come equipped with the benefit of such great camouflage.

 

 

Here a crab spider has taken its prey—one of the native bees pictured above.

 

Having eaten its fill, the crab spider discards its prey, literally throwing it to the ground.

 

It retreats closer to the center of the flower and lies in wait once more.

 

Aerial predators are abundant too. Dragonflies and damselflies (Order Odonata) have emerged from their aquatic stage within the past couple weeks to take advantage of the numerous flying insects present on Mount Pisgah. These most skilled of all insect fliers are now thought to be the most successful predator in the animal kindgom, catching up to 90% of the prey they hunt. This recent New York Times article about dragonflies is highly recommended.  Pictured here is a species of narrow-winged damselfly (Family Coenagrionidae).

 

This female Common whitetail dragonfly (Libellula lydia) sits on a dried stem, waiting for prey to fly by. Females of this species can be differentiated from males by their drab coloring; male bodies are a soft blue.

To reach this beautiful section of the Arboretum, walk up the gravel road that heads east past the Pavilion (marked “Canyon Trail” on the MPA Trail Map) until you reach the junction with the Oak Savannah Trail. Continue on past this trail and follow a dirt path as it curves to the right past a bench. About 75 yards further, you will reach the creek.  Be wary of Poison oak and make sure to stay strictly on the trail in order to protect this fragile habitat.

-August Jackson

Site Assistant