Wednesday, July 19, 2017

White Prairie Clover: An Awesome Blossom

I am not a botanist by any stretch of the imagination, but I am pretty sure that the insect magnets in the shortgrass prairie field up the hill from my home here in Colorado Springs, Colorado, are White Prairie Clover, Dalea candida. What follows is a sampling of the many bees, wasps, butterflies, flies, and other insects that come to the flowers of this plant; and a little information on Dalea in general. Much of the pollinator enhancement literature touts Purple Prairie Clover, D. purpurea, so one has to dive deeper.

A cuckoo bee, Nomada sp., forages while a male sweat bee, Lasioglossum sp., approaches

Prairie clovers are in the pea family Fabaceae. White Prairie Clover in Colorado occurs from 3,400-7,200 feet in elevation, and blooms from June to August. It is a low-growing plant, flowers on stalks up to two feet tall, but the ones I see are no more than one foot tall and sometimes difficult to discern among the tall grasses, cacti, and yucca they share the prairie habitat with. This species is widespread from the Front Range across the Great Plains, north to Saskatchewan and Wisconsin, and as far east as Tennessee, Georgia, and South Carolina.

Common Checkered-skipper, Pyrgus communis

The flowers are arranged in a cone, and bloom from the bottom to the top. The cycle can last up to a month, providing insects with pollen and nectar over a longer period than most flowers, and often at a time when few other plants are blooming. The down side to this plant, from the perspective of the photographer/entomologist is that insects quickly move to the side of the flower opposite the photographer, where they are hidden from view, then fly to another florescence and repeat. I missed a good number of opportunities because insects move across the flowers so speedily.

Male Hunt's Bumble Bee, Bombus huntii

Bees of all stripes seem to enjoy White Prairie Clover, and male bees may visit not only for nectar but for mating opportunities with foraging females. I saw far more male sweat bees, Lasioglossum (subgenus Dialictus), for example, than I did females. Even male bees can be sufficiently hairy enough to perform pollination services, even though they are not gathering pollen to feed to offspring. This is especially true for bumble bees and longhorned bees.

Sweat bee, family Halictidae

Female mining bee, Calliopsis sp.

Male longhorned bee, tribe Eucerini, family Apidae

Cuckoo bee, Triepeolus sp.

A second species of Triepeolus

Butterflies visit the flowers, too, mostly for nectar, but the caterpillar stage of some species feeds on the foliage of Dalea. This is the case for the Southern Dogface, a rather scarce species here in Colorado. In addition to the butterflies shown here, I also spotted a Variegated Fritillary making a brief stop on a blossom.

A "crescent" butterfly, Phyciodes sp.

Two Reakirt's Blues, Echinargus isola

At least one moth visited White Prairie Clover during my two separate observations: the Jaguar Flower Moth, Schinia jaguarina.

Jaguar Flower Moth, Schinia jaguarina

Wasps were highly diverse and plentiful visitors, but made some of the shortest refueling stops of all the insects observed.

Great Golden Digger wasp, Sphex ichneumoneus

Thread-waisted wasp, Ammophila pictipennis

Female Ammophila procera

Male Ammophila procera

Ammophila ferruginosa

Black & Yellow Mud Dauber, Sceliphron caementarium

Male sand wasp, Bembix sp.

Male beetle-killer wasp, Cerceris sp.

Male beewolf wasp, Philanthus ventilabris

Male thynnid wasp, Myzinum sp.

Female thynnid wasp, Myzinum sp.

Cuckoo sand wasp, Stizoides renicinctus

Flowers that are attractive to pollinators are also attractive to their predators and parasites, and that was certainly obvious during my watch periods. The bee assassin, Apiomerus sp., was somewhat surprising because the bug is so conspicuous atop such a small flower. I suspect it was having little or no success. Meanwhile, the odd, cream-colored ambush bug, Phymata sp., could achieve proper concealment, even to the point that I recall seeing only one when there were surely many.

Bee assassin bug, Apiomerus sp.

Thick-headed flies accost bees or wasps in mid-air and ram an egg between the victim's abdominal plates. The fly larva that hatches then feeds as an internal parasite. This often kills the host, but not always.

Thick-headed fly, Zodion sp.

Thick-headed fly, Physocephala sp.

My personal experience is that white flowers, or at least pale flowers, attract a far greater diversity of insects than red, blue, or purple flowers, and even more than yellow flowers in some cases. It is puzzling to me that few pollinator advocates bother to reveal that fact. Maybe because everything is bee- and butterfly-centered, and still color-intensive in the landscaping sense, white flowers get short shrift in recommendations for the garden.

Grasshopper wasp, Prionyx atratus or Prionyx subatratus

It may be worth it to harvest seeds from wild plants, but please do not dig up mature White Prairie Clover. The plant has a deep taproot. One may also wish to consult their state's Native Plant Society for potential sources of seed. The plant flourishes in full sun and dry soils, requiring only a medium quantity of water.

Green-eyed wasp, Tachytes sp.

I will try and produce more floral-themed, pollinator-rich posts in the future to help readers in making landscaping decisions that support native plants as opposed to exotic ornamentals and inappropriate cultivars. Feel free to make suggestions as to additional resources.

Mason wasp, Euodynerus sp.

Sources: Holm, Heather. 2017. Bees: An Identification Guide and Native Plant Forage Guide. Minnetonka, Minnesota: Pollination Press LLC. 224 pp. Useful mostly for Upper Midwest U.S.
Mader, Eric, et al. 2011. Attracting Native Pollinators. North Adams, Massachusetts: Storey Publishing. 372 pp. A Xerces Society guide.
EasternColoradoWildflowers
WildflowerDotOrg
Prairie Nursery

2 comments:

  1. Thank you for this post! I am a novice native plant gardener, who began for the explicit purpose of increasing the number and diversity of invertebrates generated on my land. Certainly, some plant species play host to more insects than others, and it would be good to have more information on which plants seem to provide the most benefit to the local food web. Most native plant guides I've read are targeted at supporting pollinators -- i.e., native plants that bloom throughout the season -- but do not address ways of attracting a VARIETY of pollinators. And of course, I also want to generate lots of leaf-eating insects as well! The willows, poplars, and chokecherries seem to be popular?
    I am just getting into this, but so far the plant I've noticed having gotten the most traffic (and variety) is a tall goldenrod of some sort (S. candensis maybe?).
    But thank you for the Dalea candida tip, it will join D. purpurea in my garden!
    (Also, I really enjoy your Colorado Arthropods FB page! I found your blog while trying to ID a large wasp with big green eyes, and ended up on your tachytes page.)

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    1. What you are doing is fabulous! We need more like you. :-) Thank you for the compliments on the blog and Facebook presence.

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