August 28, 2010

On Saturday I wandered down to the mailbox, camera in hand, on a dew-soaked morning that was chilly even though the sun was well up. Summer's winding down--the goldenrod has just started to bloom and the teasel has died back, but there's still some life to be found in it.

Differential grasshoppers (Melanoplus differentialis) are common pests, but here the cold nearly stilled them and they looked like intricate sculptures.

On the milkweed next to the mailbox, I found this year's first swamp milkweed leaf beetle.

Here's a field cricket (Gryllus pennsylvanicus)--in the field!

There was a lot of bird activity. The neighbor's pair of house wrens scolded as I walked past and there was a couple of chickadees feeding in the cedars. The chickadees here all appear to be Carolinas but we are within the Carolina-black-capped hybridization zone and they can't be told apart except by direct measurements.

Milkweed puzzle

The common milkweed (Asclepias syriaca) in my field is a famously toxic plant. It produces cardenolide alkaloids in its foliage, cardiac toxins that affect sodium and potassium levels and interfere with heart contractions. It also produces a sticky latex sap and leaf hairs to foil herbivory.

It is common knowledge that the Monarch butterfly caterpillar (Danaus plexippus) which feeds on milkweed has evolved to tolerate the plant's toxins, sequestering them in its body, rendering it toxic to its own predators.

In the course of wandering my field with my camera for the last year, I have found that the milkweed plant is host to many more insects than Monarch larvae. Even if I can't find anything to photograph in the rest of the field, there's always something to be found on the milkweeds. And it turns out that many of these insects pull off the same trick--consuming the plant with impunity and using the toxin to ward off their own enemies. Some of them, in addition to tolerating the cardenolides, have evolved techniques to disarm the plants other defenses. Monarch caterpillars first clear an area of hair before feeding and also cut the latex canals in the leaf, reducing the pressure of the sticky sap. Anurag Agrawal's video discusses this topic in depth (http://cybertower.cornell.edu/lodetails.cfm?id=481).

Another Lepidopteran, the Milkweed Tiger Moth caterpillar (Euchaetis egle) eats milkweed foliage.

The Large Milkweed Bug (Oncopultus fasciatus) lays its eggs on the milkweed and its nymphs, along with the adults, feed on the plant's juices and maturing seeds.

The Red Milkweed Beetle (Tetraopes tetraophthalmus) larvae bore into the stems and roots of the plant to feed.

The Swamp Milkweed Leaf Beetle (Lasidomera clivicollis) consumes the foliage and the flowers.

All these milkweed specialists advertise their own toxicity with bright, apsomatic coloration. This warns off predators that would otherwise eat them. It works so well that some non-toxic insects [again famously, the Viceroy butterfly (Basilarchia archippus)] wear the same colors to avoid predation.

The milkweed does depend on insects for pollination, and produces large, fragrant flower clusters. However with the exception of the occasional Monarch adult, the pollinators I've observed are different species than the milkweed specialists above.

It makes me wonder how this is working for the plant. It spends energy producing toxins and defenses that many insects have evolved to disarm. The plant toxins protect the insects from vertebrate predators, but the insect work-around must be fairly easily developed since it occurs in at least three orders. And while the milkweeds do survive to set seed, by the end of the summer they are pretty ragged. Are milkweeds just barely protecting themselves against these insect specialists, engaged in an arms race with them as Anurag Agrawal suggests? Do these specialists benefit the plant in some way? Or is the milkweed protecting itself against some other rapacious insect that is completely foiled by the plant's defenses? Vertebrate herbivores--geese, bison, or deer? Food for thought.

Killdeer Plains--August 15, 2010

On another humid, overcast morning, Steve and I set out for Killdeer Plains. The 9000 acres are managed for wildlife and hunting by the ODNR. It occupies an area that was formerly prairie and some remnant spots are managed for prairie vegetation. Even though it is only 1/3rd the size of the original prairie, the open vistas are startling to see in Ohio.

We usually come here to see the birds. The raptors are spectacular--there are nesting bald eagles here and in winter, scores of harriers and rough-legged hawks, and once we got a good look at a merlin. Owls too--it’s a well-known winter roosting spot for long-eared and northern saw-whet owls, and short-eared owls hunt the fields. In winter, flocks of horned larks, snow buntings, and longspurs are common. We nearly always see trumpeter swans, and once we saw American white pelicans on the marsh.

Although we did startle a great blue heron, today belonged to the insects. Mixed groups of puddling butterflies were everywhere. Male butterflies do this to ingest minerals which are then transferred to the females in sperm to help improve egg viability.

Buckeye (Junonia coenia) and pearly crescentspots (Phyciodes tharos).

Red-spotted Purples (Basilarchia astyanax) and Little Yellows (Eurema lisa).

Buckeye

Viceroy (Basilarchia archippus), which famously mimics the toxic Monarch butterfly.

We missed the peak of the prairie flowers, but there were still some in bloom:

Swamp Milkweed (Asclepias incarnata), with Pearly Crescentspot,

Hairy Sunflower (Helianthus mollis),

Partridge-pea (Chamaechrista fasciculata).

Other insects were abundant too. Each time we stopped the car, horseflies swarmed around in alarming numbers.

Ailanthus webworm moths (Atteva punctella) flocked to the common milkweed.

Steve got this picture of a damselfly near the marsh.

I found a robber fly out among the prairie flowers. This one appears to be a bee killer (Promachus fitchii) which does just that, scouting its prey from exposed vegetation.

August 14, 2010

I went out yesterday on another sodden, hazy morning not expecting to see much. The only plants blooming in the field right now are ironweed and Queen Anne’s lace--the milkweed’s long done.

But you never know. I did find some milkweed tiger moth caterpillars (Euchaetias egle)--a showy caterpillar that metamorphoses to a pretty nondescript adult moth. Years ago before the milkweed took off in the field, I tried to grow some butterfly weed (another milkweed) in my garden. It was never very happy in my shady site, and then one summer, a whole clutch of these caterpillars ate it right to the ground. Sometimes when you plant for wildlife, you get what you ask for!

Halfway down the driveway and just as I was about to turn back, a doe and fawn crossed the road and came up the hill toward me.

This fawn’s spot pattern doesn’t match that of either of the fawns I saw in July, so this is a different family.

They got pretty close before the doe finally scented me. It scared the snot out of her--she didn’t stop snorting until she got to the other side of the soybean field behind the sumac jungle!

Butterfly tree

I’ve had a creepy curiosity in my yard all summer that I finally took some time to examine this week. About a month ago I noticed Red Admiral (Vanessa atalanta) butterflies in the front corner of the yard along the edge of my front field and the neighbor’s soybeans. I know from childhood that they are territorial and bold around people and also that you can find them in the same place every evening. Last time I mowed I got strafed by butterflies there, so I figured I’d go look around when I had time.

When I went out in the evening, I found a group of 5-10 butterflies, mostly anglewings--Commas (Polygonia comma) and Question Marks (P. interrogationis), but also a Red Admiral and a hackberry butterfly (Asterocampa celtis) flying around a ragged, half-defoliated slippery elm (Ulmus rubra Muhl.) sapling in that corner. The butterflies would fly around in groups and then occasionally land on the tree. Elm species are host plants for the anglewing caterpillars, but not the Red Admiral. All of these species are territorial as adults and the adults feed on tree sap as well as rotting fruit and dung. As I watched, I noticed bees and flies hanging around the trunk too. A few birds flew in and out of what was left of the canopy--I think they were female indigo buntings.

Question Mark Butterfly

Hackberry Butterfly

Once I got around to the soybean side of the tree where I could get close look, it was clearly a sapfest. Butterflies swooped in and out, and around my head, a troop of horseflies swarmed on the trunk for minute, then disappeared, and a bald-faced hornet made an appearance. There was even an adult cicada in the branches. There was a lot of activity and buzzing around--there was a definite “creep factor” at work here!

Horseflies (Tabanus sp.). Only the female horsefly drinks blood, so these are probably males.

Cicada adult

The Sumac Saga

When I moved here 15 summers ago, the front acre was a long, sloping lawn with young conifers planted along the eastern boundary. I decided to let it go wild, just planting more trees and shrubs to fill in the boundary, making a mixed hedgerow. Now it is at an old-field stage, filled with milkweed, goldenrod and asters and young ash, mulberry, and red-cedar saplings.

About 10 years ago Steve planted a staghorn sumac (Rhus typhina L.) fruit in a coffee can and left it on his back porch. Two years later, it sprouted and we transplanted it into the hedgerow where it thrived. I really thought this was a good idea at the time. It’s native, and the sumac I’d seen along roadsides grew in small groups with an attractive, open, antler-like form.

Unfortunately though, despite the annual beating it takes from the deer, it has formed a dense clonal thicket and is marching tumor-like across my field. None of my guide books mentioned this tendency (although I have recently found this information online) and I had a bad moment a few years ago of thinking we had planted tree-of-heaven by mistake. But no, sumac it is.

It’s beautiful in the fall, and the wildlife does make use of it, but nothing else grows within it’s boundary.

I’ve read that it can be controlled by cutting it back in July and August, but that the sap can produce a poison ivy-like rash. I don’t want to eradicate it entirely, but I’m not sure how taxing it would be to have to cut it back each year. The clones are apparently relatively short-lived and it will not thrive in shade, should the saplings manage to top it. But for now it’s joined in the battle among the other invasives in this field--multiflora rose, Canadian thistle, and teasel competing for this space.