Saturday, August 23, 2014

Waste not, want not.

Active paper wasp nest
Last week I was in Wood River, Nebraska gathering with friends and colleagues at this year’s “Patch Burn Grazing” working group meeting.  I used to live on-site where the meeting was being held, so it was pleasant to return. It was all much as before I'd left. The cattle still worked the tallgrass, the road was still gravel, and the 70's-era carpet in the main building still resembled multi-layered and lush green moss.

I saw some familiar faces, one of whom pointed me to a relatively uncommon natural phenomena. Leaf cutter bees had decided to lay eggs in abandoned paper wasp nest. Unfortunately, I was unable to capture a picture of these crafty mothers exiting their chosen tunnels, but I did get a picture of the distinctive leaf caps sealing the ends of these structures. You can compare the leaf cutter bee filled nests to the images (taken from a previous post) of an active paper wasp nest.

I also happen to adore leaf cutter bees. They have a BIG personality for such a little arthropod. Leaf cutters have a distinctive high pitched tone to their buzzing. Once you learn to recognize it, you can pick their hum out of a crowd of pollinators in a garden. I have written about them before

Recycling a la leaf cutter bee
A quick google search turned up results suggesting that practice of re-purposing of old paper wasp nests by leaf cutter bees is perhaps uncommon but not undocumented.  I don't know why they would choose this nest instead of using some of the many sumac stems or downed cotton woods scattered around the site. Perhaps the bees were attracted by the number of tunnels? I'd be curious to learn how many larvae make it through the Nebraska winter in this seemingly flimsy shelter. I'll have to ask my Nebraska friends and colleagues to keep an eye on it.

Saturday, August 16, 2014

A wet summer in the Ozarks

A luna moth- quintessence of the southeast's rich broadleaf forests
I recently visited western Arkansas for a pollinator workshop, and I took the opportunity to do a little camping in the Ozarks. I'd never been before- most of my life up to this point I've been closer to the southern Appalachians or the Front Range. I have been curious about this green spot on the map, and all the Texans I've asked about it described it as an idyllic, lush summer retreat.

The Arkansans could do with a little less lushness this year. It rained every day I was in Arkansas, and since the summer began there has been no six-day stretch without precipitation. "So, what's the big deal?" you might ask. Well, no one has been able to cut hay. If they do cut hay, they run the risk of it mouldering in the field. This is something of an economic hit, and one wonders what it will mean for the cost to keep livestock over the winter. Beef is one of Arkansas' major industries.

Viola pedata, birdsfoot violet
Economics aside, it was exciting to be somewhere so overtly green. We've had a dry summer in Texas (which in itself is not unusual), and this season's drought is stacked on top of a multi-year moisture deficit. Last I checked, Fort Worth was still about 10" behind in terms of annual precipitation in this year alone. For your reference- we only get about 32" total. 10" is a big deal.

The view from 'Sunrise Point'
I quite enjoyed the Ozarks despite the rain. The forests were similar to those of the southeastern mountains. A few key species were absent, most notably the tulip poplars, but the oak-hickory canopy was there. So to the understory of sassafras.

More text and pictures of the Ozarks after the jump.


Wednesday, August 13, 2014

Grazing in Oklahoma

They were using horses to move the cattle to the corral in the distance
I'm spending most of the month of August on the road, just popping home long enough to do laundry and swap out gear. Last week I visited Kerr Ranch in Oklahoma and the Booneville Plant Materials Center in Arkansas. My work has been focused lately on exploring pollinator habitat enhancement with land management techniques like grazing and fire, so visiting the Kerr Center for Sustainable Agriculture in Poteau, Oklahoma was a real treat.

Opening 'maypop' (Passiflora incarnata) on fence. Larval host to gulf fritillary.
Poteau sits on the Poteau River in the Ouachita Mountains, a western extension of the Ozarks. I was shocked at how this land resembled the Virginia piedmont near where I grew up. The trees were different, but the terrain was much the same. David Redhage, the Kerr Center's agricultural economist and Director of Ranch Operations, drove me around to see some of the pollinator habitat on the Center's 4,000 acres. The Kerr Center practices rotational grazing and silvopasture. They also have some acres devoted to loblolly pine. Most interesting to me, they were experimenting with incorporating pollinator plants in their hedgerows, fence lines, and native pastures. David's had a personal interest in pollinators since the 90's, so he's really jumped in with both feet now that pollinators are an ecological buzzword. 

I get a lot of joy out of working with ranchers on native pastures because there is so much potential. Some level of careful grazing can often increase the presence of blooming plants in our native prairies. The landowner can improve wildlife habitat while still making a living. The theory is this: our tallgrass and mixed grass prairies evolved with grazing and fire. Without grazing, grass has the competitive edge over forbs. It grows faster and shades out our other natives. Cattle and bison preferentially eat grass over most forbs, so light to moderate grazing tips the competitive balance back in favor of flowering plants. Of course, you can over do it. Overstocked and overgrazed pastures can be moonscapes. One must be conscientious. 

And the Kerr ranch has been conscientious. They're following the basic range precept of "take half, leave half". It's working here. I took a series of pictures along the pulled electric fence line in their grazed remnant prairie, showing the impact of grazing on the grass-forb balance. Here are some images demonstrating the excellent job that the folks at the Kerr Center are doing with their native pasture:

Ungrazed above red line, grazed below
Note the rank grass above the grazed line. This is what we call "undergrazed". Coming from the east, it was a real cultural adjustment for me to recognize the place grazing has in maintaining healthy grasslands. Regional differences in accepted habitat management practices are something I butt heads with regularly when making management recommendations.

Ungrazed above red line, tilled and planted below
This line here is one of David's experiments. He wanted to try to re-introduce some plants that had dropped out of the native pasture during its years of neglect. He sowed partridge pea (pictured) and compass plant, among others. You can see the dense grass above the till line, and his planting below. The next two pictures are of the grazed portion of the pasture. You can see how the cattle ate around the forbs, focusing their attentions on their preferred grasses.

Grazed. Note that the cattle ate around the forbs.
Another shot of the grazed half
Grazed. Note the circled cow pie.
In case you are still incredulous: here's a cow patty in the grazed sector, right at the base of a nice clump of blazing star. 

More pictures of Kerr Ranch after the jump. 

Wednesday, August 6, 2014

Potter wasps and bee tongues

Potter wasp nest on the underside of a mexican plum leaf
I was reviewing some photos I took a couple of weeks ago at the Fort Worth Botanic Gardens when I stumbled upon this picture of a potter wasp nest. It had been tucked into the underside of a leaf on a Mexican plum tree, completely concealed from most perspectives.  I only noticed it because I had been examining curled leaves looking for caterpillars. Potter wasps (Euminidae) use mud to build these structures resembling clay pots (hence their name). After depositing her eggs, the female provisions them with caterpillars and other soft insects. 

Bee assassin eating a captured potter wasp
Potter wasps are quite common, and I often see them lurking in my garden hunting pest insects. Lately they’ve been hanging around my stricken-looking turk’s cap (Malvaviscus arboreus var. drummondii). I hope they get whatever’s been gnawing it. A few months ago I posted a picture of a bee assassin eating one of these artistically inclined insects on prairie parsley. Here’s a re-post of that image: 

Wasps are predatory, but they only hunt to feed their young. At adulthood they switch from a protein-rich insect diet to vegetarianism and flower nectar. Like most wasps, potter wasps have short tongues and can only reach the nectar on flowers with short corollas. Growing shallow flowers in the aster family is a good way to support populations of this beneficial insect.

Bombus pensylvanicus and her long tongue on some sort of white salvia
Conversely, many bumble bees have rather long tongues. The Bombus pensylvanicus worker, pictured at left, is a good example. She was very obliging and flew from flower to flower with her long tongue partially extended. While bumble bees also feed on asters, they have additional resources available to them that wasps are unable to extract. These long-corolla flowers that hide their nectar resources at the end of tube do so presumably to favor bees over other less effective pollinators. Lucky for the bees! 

Monday, August 4, 2014

Chasing butterflies at Fort Worth Nature Center

Eastern swallowtail (male?) resting on oak.
I took advantage of the unseasonably cool weather Saturday morning to chase butterflies around Fort Worth Nature Center. I only tried to catch them with my camera, but I think next time I'd do better to bring a net-- they are fast and a little too wary for me to sneak up. I'm still learning butterfly ID, and taking pictures and flipping through my guidebook has been a pretty effective way to make species stick.
Along the causeway. River on the right, marsh on the left.

I wasn't the only person out enjoying the brief reprieve from the heat of Texas summer. One couple had undertaken the marital trial-by-fire of paddling a two-person canoe (much to the amusement of the fisherman and anyone else within earshot). For my own part, I was hot-footing to dodge fire ants and ant lion pits.  Trumpet creeper, button bush, and liatris were all still blooming along the river despite being deep in the late summer dormant season.

Gulf fritillary (Agraulis vanillae) on liatris
Specifically, I was out looking for the gulf fritillary. I've seen them in parks and around town, but they don't sit still much. When they do it's mainly up high in a tree out of reach. The picture at left is as close as I've been able to get. Unlike the northern fritillaries whose larva feed on violets, gulf fritillary caterpillars only eat passion vines (Passiflora spp). How tropical. Gulf fritillaries, like squash bees, have probably expanded their range with human settlement. In both cases, the domestication and propagation of their host plants in our gardens has allowed these pollinators to move into new landscapes [1].

Grasshopper on button bush. What is he doing?
Gulf fritillaries are not closely related to 'true' fritillaries, and they are the only extant representative of their genus. Generally lumped with long-wings, their nearest relatives are tropical in distribution. Gulf fritillaries themselves are migratory, and they have been known to make exploratory forays as far north as the central plains [2].  However, their US population centers are in the southern third of the lower 48, in areas where their larval host plant is either native or naturalized.

It's amazing to me how most butterflies are quite specific in their larval host plants. As first glance, it seems like a high-risk strategy. Why specialize at all when specialization means fewer food options? There must be some benefit, or host plant specialization wouldn't be the dominant strategy.

After doing a little digging in the literature, it appears that host plant chemistry and avoidance of parasitoids are proposed drivers for female butterflies to lay their eggs on one type of plant [3, 4]. Most of us are familiar with Monarch butterflies and how they use toxic alkaloids from the milkweed they eat as caterpillars to discourage predation. The gulf fritillary uses Passiflora spp. alkaloids towards similar ends. Unsurprisingly, tropical lepidoptera are more likely to be specialized than their temperate kin [4]. Dyer et al. hypothesized increased competition as the driver of increased host plant specialization at lower latitudes [4], so perhaps it is the opposing pulls of predation and resource availability that drive this selectivity. Who knows, but it's certainly fun to ponder!

Sulphur (little yellow?) butterfly next to leaf

  1. Graves, Sherri D., and Arthur M. Shapiro. "Exotics as host plants of the California butterfly fauna." Biological Conservation 110.3 (2003): 413-433. 
  3. Thompson, John N., and Olle Pellmyr. "Evolution of oviposition behavior and host preference in Lepidoptera." Annual review of entomology 36.1 (1991): 65-89.
  4. Dyer, Lee A., et al. "Host specificity of Lepidoptera in tropical and temperate forests." Nature 448.7154 (2007): 696-699.