Julie Craves

« Older Entries
Newer Entries »

Frass Baskets

By

Tuesday, August 30th, 2011

My research centers around urban ecosystems and invasive species. Typically, this means birds and non-native fruit, but I’ve done a fair amount of insect work and am always on the lookout for intriguing, exotic urban bugs. A few years ago, at a meeting of the Michigan Entomological Society, I saw a presentation about a moth introduced to North America around 2002. It’s been estimated that nearly 100 species of moths have been introduced on this continent from Great Britain alone. This particular moth, the Greenish-Yellow Sitochroa Moth, Sitochroa palealis, is also native to Great Britain, and its range extends to eastern Russia and south into North Africa; there are also records from the Far East.

Although my mind went a little numb listening to the details of the adult moth’s genitalia structure, I perked up when I heard that the larvae have a distinctive lifestyle. They feed on the flowers and seed heads of plants in the Umbelliferae (Apiaceae) family. In North America, the dominant host is Daucus carota, Queen Anne’s Lace, one of the most familiar non-native wildflowers in the U.S. This feeding habit accounts for the insect’s other common name, the Carrot Seed Moth.

The presenter at the meeting told us to look for larvae of Sitochroa palealis in the cup-shaped seed heads of Queen Anne’s Lace, as the moth was established in Michigan, as well as Illinois, Indiana, and Wisconsin. I spent the next two years peering into hundreds of seed heads, to no avail.

Eventually, my interest in finding the caterpillars waned, although I still looked at Queen Anne’s Lace seed heads out of force of habit. Last summer, I was walking through an old brownfield site along the Detroit River when I noticed a pile of frass – insect poop – in a seed head. I peeked inside, and there it was: a fat, speckled Sitochroa palealis larva. In fact, nearly every nearby Queen Anne’s Lace seed head acted as a basket of frass produced by a resident caterpillar. Often the caterpillar was hidden, but the frass was very conspicuous.

I never noticed any Sitochroa palealis adults at that site, but within a month I did photograph a rather boring-looking diurnal moth nectaring on Culver’s Root in my garden. It turned out to be the Carrot Seed Moth. It was quite fresh, and while I didn’t find any larvae in the neighborhood Queen Anne’s Lace, I now know what to look for.

And you do, too. In late summer, look for frass-holding Queen Anne’s Lace seed heads in the upper Midwest. In addition to the four states mentioned above, I’ve seen photos from Iowa, Pennsylvania, and Ontario. The Carrot Seed Moth could be coming to an old field near you!

Tags: , ,
Posted in Julie Craves | 4 Comments »

Robber Flies

By

Thursday, August 18th, 2011

The insect family Asilidae is known as the robber flies: an ordinary name that is nonetheless evocative. Are robber flies masked? Stealthy? Whom or what do they rob?

Worldwide, there about 7,000 species in over 500 genera. The name infers some sort of piratic behavior, but robber flies don’t steal prey from other creatures — they hunt for themselves, and very well. Their usual modus operandi is to take up a position on a twig, leaf, or stone (each type tends to have a preference) and fly out to grab a passing insect. When prey is captured, a robber fly stabs its victim, injects it with a neurotoxin which immobilizes it, followed by enzymes that liquify the prey’s innards, which are then slurped up by the fly.

Most robber flies have a distinctive pointy-faced, large-eyed look that reminds me of the old Spy vs. Spy comics from Mad Magazine. Some are very large – up to 4 centimeters – and have been known to attack hummingbirds, or bite rough human handlers.

Robber flies of the genus Diogmites are called hanging thieves. They often consume their victims while hanging by one or a few of their very long legs, while holding their prey with those legs not so engaged.
Flies of many families mimic bees or wasps, better to fool their prey if they hunt in the open. Lots of robber flies are master mimics, particularly those in the genera Laphria and Mallophora, which are very credible and sometimes beautiful imitators of bumblebees or hornets.

Larvae usually live in soil or decaying wood, mostly feeding on the eggs or larvae of other insects, and overwinter as pupae.
You really don’t sneak up on robber flies, with their excellent eyesight. But many are pretty tolerant so long as you don’t make any fast moves. I’ve even had them ride around on my insect net handle. So next time you encounter one of these predatory flies, feel free to steal a look.

Tags: , ,
Posted in Julie Craves | No Comments »

That’s Mitey Interesting!

By

Wednesday, August 3rd, 2011

A couple of years ago, my husband and I set out to see how many species of wasps and bees we could document with photos in our small urban yard. We’re up to nearly 90, which covers all the conspicuous and easy-to-ID stuff. One of the challenges has been to differentiate among all the black and yellow wasps. The yellowjackets and other hornets aren’t too bad, but there are many species of potter and mason wasps in the family Eumeninae that are very similar except for the number or arrangement of yellow spots or stripes on a black body.

A series of good photos from multiple angles often cinches the ID. Occasionally we have to resort to netting an individual, chilling it, and looking at some features under a microscope while consulting detailed keys.

That is how I discovered a remarkable structure found on some bees and wasps, especially the Eumeninae: the acarinarium.

Acarinaria are special structures on the body of bees and wasps that function exclusively to harbor mites. They may be a hollow chamber, a hairless area that is easy for mites to cling to, or a series of pits along the edge of an abdominal segment. In my photo of the potter wasp above, the mites are carried on the thorax.

The mites on the wasp are benign – they are in a non-feeding phase while on board. If the mites are on a male wasp, they transfer to the female when the wasps mate. Potter and mason wasps are not social wasps; each female constructs a separate nest made of mud, in the ground, in wood, or some other cavity. As the female provisions her nest, the mites disembark. There they continue to develop, and once the immature wasp pupates, the adult mites feed on the young wasp. Amazingly, this apparently does not harm the wasp. A new generation of mites hitches a ride out of the nest on the wasp when it emerges.

Evolving modified body parts to accommodate mites makes sense so long as the mites are beneficial. It’s presumed that the mites perform a service in the nest prior to them feeding on the wasp, such as combating fungi, predators, or parasites that might damage wasp eggs or young. Each genus of wasp is associated with a particular genus of mite, so this relationship is very specialized. Yet the precise mechanism of this mutualism is still poorly understood.

Now, do we start a mite list for the yard?

Tags: , , , ,
Posted in Julie Craves | 6 Comments »

The Smallest Dragonfly

By

Thursday, July 7th, 2011


I know that for an ornithologist, I write a lot about insects. My bird research requires lots of long-term data gathering. On the other hand, the work I have done with insects, especially dragonflies and damselflies, provides frequent episodes of instant gratification. I’m currently working on a paper documenting the dragonflies and damselflies of my urban southeastern Michigan county. Over the last ten years, my husband Darrin and I have discovered nearly three dozen new species for the county, including five state records. Pretty satisfying!

Darrin and I make good partners in this regard. He likes going after the bigger, showy species. His nom de plume on our dragonfly blog, Urban Dragon Hunters, is Stylurus. This is a genus of hanging clubtails, fast flying and high perching dragonflies mostly found along big rivers. I, on the other hand, often spend time “thinking small” and searching for less conspicuous species. This usually means delicate damselflies, but can also include small dragons. Thus, my handle at Urban Dragon Hunters is Nannothemis, the genus of the smallest dragonfly in North America, the Elfin Skimmer (Nannothemis bella).

These little odes are less than an inch long and are found flitting just inches above the ground through vegetation in sphagnum bogs and similar habitats. They are perfect miniatures of their larger relatives in the family Libellulidae, which includes familiar robust species found on nearly any summer pond, such as Twelve-spotted Skimmer or Common Whitetail.

Male and female Elfin Skimmers are highly dimorphic. Some people believe the coloration of the female is meant to mimic a wasp. Males are dull gray, acquiring a bluish appearance as they mature.

Despite their diminutive size, they share their family’s territorial and feisty manner. Elfin Skimmers are the tiny masters of their little domains, where boggy puddles are their oceans, bulrushes are like redwoods, and mosquitoes dare not enter, since they represent entire meals.

Tags: , ,
Posted in Julie Craves, Uncategorized | 2 Comments »

Another Country Heard From

By

Friday, June 17th, 2011


Viburnums are among my favorite shrubs. There are over 150 species; a large number are native to North America. Most are spring flowering and attract pollinators, and many bear fruit consumed by birds. I have several species of native viburnums in my yard, dominated by arrowwood, Viburnum dentatum.

Last year I noticed some of my arrowwood shrubs had many leaves that were nearly skeletonized. We use no chemicals on our property, so the handiwork of insects isn’t unexpected. This spring, all of our arrowwoods, as well as highbush cranberries (Viburnum opulus/trilobum complex), showed similar damage. The culprits were apparent underneath each leaf: tiny caterpillar-like bugs that were gray or yellow with black dots. I assumed they were some kind of sawfly larvae. Sawflies are actually not flies, but in the order Hymenoptera (with ants, bees, and wasps). Some species have larvae that look like butterfly or moth caterpillars, and they often feed in groups that can defoliate their host plants.

A little research proved me wrong. The viburnum attackers were larvae of the viburnum leaf beetle (Pyrrhalta viburni). This beetle is native to Europe and Asia, and was first found in North America around 1947 in Ontario, although it was another 30 years before established populations were reported. It is now present in much of the northeast, and as far west as here in Michigan, where it was first observed in 2007. It will no doubt continue west, but how far south it goes will probably be limited by the fact that the eggs must overwinter at cool temperatures.

Host plants are nearly exclusively viburnums, with arrowwoods and highbush cranberries being most susceptible. I’ve yet to see any adult viburnum leaf beetles. They’ll come along shortly, once the larvae have finished developing, pupate in the ground, and emerge ten days later. I’ll be on the lookout, because they could be easy to overlook at less than a third of an inch long and a non-descript brownish color. As in their “youth,” the adults also feed on the leaves of their host plants. Heavy infestations of larvae and adults can defoliate entire shrubs which, if it occurs over two or three seasons, has the potential to kill the plant.

I’ll employ two strategies to control this non-native pest in my yard. One is already in place – I don’t use pesticides so I have populations of beneficial insects. The larvae of lacewings and lady beetles (including, ironically, the introduced Asian lady beetle, Harmonia axyridis, considered a pest itself) will feed on the larvae of the viburnum leaf beetle. I’ll also examine my shrubs for signs of egg laying, and trim those twigs off. This will be just another challenge in our homogenizing world.

Tags: , , ,
Posted in Julie Craves | No Comments »

Handsome and Hairy Harbingers

By

Wednesday, April 20th, 2011


We all have our waymarks that guide us through the seasons. For me, one sure sign that winter is fading is the appearance of Bombylius bee flies in sunny woodland patches. I’m not the only one: early western entomologist Frank Cole described them as the “hairy and handsome harbingers of spring.”

The Bombylius I watch for is Bombylius major, the Greater Bee Fly. They look like little plush toys, with a long, thin, proboscis. They are common across North America and also occur in Eurasia. Their early spring activity is timed to coincide with that of solitary bees, such as those in the genus Andrena. As adults, Bombylius feed on nectar by hovering over early spring flowers. But their larvae are parasites in the nests of solitary bees, feeding on the food stores and larvae of the hosts.

Thus, one sees adults Bombylius prospecting for the burrows of solitary bees before the holes are sealed up. I’ve watched them searching for burrows, investigating what I presume must be likely-looking (from a bee fly’s point of view) holes, the forceful breeze from their wings tossing and scattering grains of soil as if a tiny tornado was attacking a square-inch patch of ground. It would seem most straightforward if Ms. Bombylius just went directly into the nest burrow, but I suppose that the hosts have all sorts of defenses against such an intrusion. Instead, the female Bombylius hovers over the hole and flicks her eggs inside. Females of many bee fly species pack sand grains into a special abdominal chamber so that they stick to her eggs. Presumably this gives them heft or prevents dessication.

Other bee flies in the Bombyliidae family occur throughout the spring and summer. Many are parasites on bees like Bombylius major, others target grasshoppers, tiger beetles, moths, or other insects. Some bee flies are very convincing bee mimics and all, to me, are fascinating!

Tags: , , , ,
Posted in Julie Craves | 1 Comment »

And They All Fall Down

By

Thursday, March 31st, 2011


Southeast Michigan is ground zero for a tiny beetle, the Emerald Ash Borer, or EAB for short. If you haven’t heard of them, you will. This Asian import feeds on all North American ash tree species. The adults will eat the foliage, but the wood-boring larvae do the most damage, feeding just under the bark on the phloem, essentially girdling the tree and killing it.

EABs were first detected in North America around Detroit in 2002. Within just a few years, half of all ash trees here were dead, and now ashes are functionally extinct in southeast Michigan. That’s right. Street trees, forest trees, green ash, white ash, black ash. All gone. EAB has now been found in 13 states, and Ontario. Within 30 years or so, all Fraxinus will likely be wiped out from the continent.

Adult EABs can fly, of course, but the spread has been hastened by the transportation of firewood, despite all efforts to outlaw it. Maps of satellite EAB populations show a pattern of dispersal to campgrounds within one or two days’ drive from established populations. No amount of prophylactic ash clearing or pesticide injection can counter humans determined to save a few bucks by smuggling firewood on a camping trip (a government inspector found someone lowering their child into a dumpster to retrieve their confiscated firewood!).

As an ecologist, I wondered what would happen with the loss of one of the most abundant tree genera in my area. I expected perhaps an increase in woodpeckers as they fed on EAB larvae. Since housing shortages are often a limiting factor for cavity-nesting birds, I thought I might see increases chickadees and nuthatches as ashes died and rotted.

Only the first scenario has played out so far at my study site. There was a temporary uptick in woodpecker numbers from my long-term baseline data. But, unexpectedly, dead ashes did not remain standing much past two years post-death, and tended to fall over right from the roots. Many of the trees are still relatively intact, but horizontal. This dramatic opening of the canopy has facilitated sprouting of many light-loving non-native shrubs. Native hardwood tree saplings are being eaten by deer, which have found the more open woodlands very appealing. Thus, most woodlots around here have been remarkably transformed.

There is one more ecological scenario unfolding. A paper published last year in the journal Biological Invasions described nearly 300 species of arthropods associated with ash trees in North America. Of those, 43 native species are totally dependent on, and so are at high risk of becoming endangered or extirpated. About two-thirds are flies, beetles, and butterflies or moths. Another 17 species of arthropods are biphagous – they use ash and just one other host. If losing a suite of ash-dependent species isn’t bad enough, what happens when these other species lose ash, and become entirely dependent on their alternate hosts, such as fir or lilac?

A century after we lost the American chestnut, we are poised to lose ash trees and the often-overlooked biological diversity associated with them. Be on the lookout – these cascading effects are probably coming soon to a forest near you.

Gandhi, K. J. K., and D. A. Herms. 2010. North American arthropods at risk due to widespread Fraxinus mortality caused by the alien emerald ash borer. Biol. Invasions 12:1839-1846.

Tags: , , , , ,
Posted in Julie Craves | No Comments »

Architects of Sharper Forests

By

Wednesday, March 2nd, 2011

White-tailed deer are known as ecosystem engineers – species that modify the habitats in which they occur.

Michigan, for instance, has almost twice as many deer as it did in the 1880s, which was after extensive logging created lots of appealing habitat for them. Of course, 130 years later, there is a lot less habitat for all wildlife. Deer overpopulation in urban areas is particularly vexing. Even supposing everyone could agree that controlling their numbers is the right thing to do, the logistics are daunting; safely removing deer when homes and people so close by is sometimes not even possible.

This proximity to residential areas also means that there is less for deer to eat in the surrounding landscape, so urban parks and natural areas – which are often small or fragmented – are especially vulnerable to the “engineering” activities of deer.

In my area, it’s not hard to see which woodlots have received long-term attention by deer. If it’s a spot that I’ve visited over the years, I can tell what has gone missing. The absence of trillium and other spring wildflowers that are favored by deer are often indicators of a deer herd, but in very urban areas these plants may not have been present to begin with. Instead, I just look for what is there: thorns.

Thorny plants are avoided by deer, and flourish in over-browsed woodlots. As the deer herd has increased in my area, a number of well-armed native plant species that used to be scarce in my area are now becoming common.

One is pricklyash (Zanthoxylum americanum). I recall looking all over metropolitan Detroit years ago, to no avail, for a stand of pricklyash, a host plant for Giant Swallowtail butterflies. Now pricklyash is popping up all over. Greenbriars or cat briars (Smilax species) are vines that I rarely used to see around here. The super-spiky bristly greenbriar (S. tamnoides) is now easy to find, although the unspined greenbriars such as the smooth carrionflower (S. herbacea), which deer do like to dine on, are still infrequent. Bramble patches of wild raspberries and blackberries are becoming more extensive, too.

More troubling is the proliferation of non-native spiny species, especially multiflora rose (Rosa multiflora) and barberry (Berberis species). Both of these also provide fall and winter food – rose hips and fruit – for birds, who aid in their dispersal, creating a sort of positive feedback loop with negative results.

Deer are beautiful animals. I miss the days when glimpsing one was a special treat, and when I could walk though the woods, missing the points.

Tags: , , ,
Posted in Julie Craves | 1 Comment »

Of Fruit and Flowers

By

Friday, February 4th, 2011

These are the dog days of summer…in the southern hemisphere. We need a winter equivalent here to signify these short, cold, and above all, very gray days as the calendar flips from January to February.

One thing that characterizes these mid-winter days for me is that monochromatic tedium of gray: gray branches etched against gray skies. At this point, birds have stripped away the fruit from dogwoods, cedars, hawthorns, and crabapples. Even the fruit of introduced plants such as honeysuckles, buckthorns, and Asiatic bittersweet – so abundant in urban areas – is for the most part long gone.

Just about the only splash of vegetative color is the red hanging clusters of fruit from the highbush cranberry, Viburnum opulus. (The taxonomy is a little tortured – V. opulus is the introduced European shrub, while the native variety is sometimes known as V. trilobum. They’re now usually considered subspecies; in much of the northeast you might find one, the other, or hybrids.) Although it gets picked at occasionally by birds after it ripens in fall, most highbush cranberry fruit isn’t consumed by birds until early spring.

I had always heard the fruit on highbush cranberry remains all winter because it didn’t “taste good” to birds until it had frozen and thawed multiple times. In fact, studies with captive American Robins and Cedar Waxwings determined that they preferred fall fruit in side-by-side trials. Sugars in highbush cranberry fruit do concentrate over the winter due to dehydration, but the chemical composition remains the same, and songbirds, in any case, don’t have much of a sense of taste.

The real reason birds don’t eat highbush cranberry fruit until spring is a little more complicated. The fruits are very acid and low in nitrogen. Birds need a supplemental source of protein to properly metabolize highbush cranberry fruits. In early spring, this protein source is often pollen, in the form of the insignificant-looking flowers of trees like cottonwoods, maples, and oaks.

This is a pretty clever strategy on the part of the Viburnum. In the fall when the fruit ripens, there is a whole smorgasbord of other fruit for birds to choose from. By retaining fruit until spring, highbush cranberry reduces the competition, and hones in on a very efficient seed disperser: the Cedar Waxwing (or in Europe, Bohemian Waxwing). In spring, at a time when many other bird species are beginning to rely on insects for food, waxwings remain mostly dependent on fruit, and highbush cranberry has set the table.

When a flock descends on a patch of highbush cranberry shrubs and goes to town on the fruit, you might also note that they make frequent forays into neighboring trees to partake in a little meal of pollen, completing their dietary requirement. As is their habit, waxwings wipe out a patch of berries and then go on their nomadic way, distributing Viburnum seeds far and wide, just as nature planned it.

Tags: , , ,
Posted in Julie Craves | 2 Comments »

Winter Wrens. The Other Ones.

By

Wednesday, January 19th, 2011

Although I’ve seen fewer than half of the world’s species, I’ve never met a wren I didn’t like. Whether skulky or conspicuous, they always seem full of personality.

For instance, nothing brightens up a gloomy Michigan winter day quite like a sassy Carolina Wren. Their rich, chestnut coloration seems especially warm against the leaden landscape. When Walter Barrows wrote about Michigan’s birds in 1912, this was considered the least common wren in the state – at a time when Bewick’s Wrens were still found here. Carolina Wrens have a tough time in our climate, and it’s thought that warmer winter temperatures have facilitated a northward range expansion over the past century. By the 1970s, Carolina Wrens were locally common well into northern Michigan. Still, they are susceptible to population reductions in severe winters.

With the onset of very cold weather, the neighborhood wrens (inevitably a pair, sometimes a whole family) show up at the backyard feeding station. The woodpeckers and nuthatches provide stiff competition for the suet, so I will often put live mealworms on my office windowsill for the wrens. If I’m not prompt in my dispensing of these treats, impatient wrens scold me, bobbing up and down in fussy annoyance on my sill.

One especially harsh winter, a pair of Carolina Wrens, which my husband and I had banded, spent many days at the windowsill diner. The following winter, I wasn’t too surprised to sit down at my desk one morning and find two wrens expectantly peering in the window. What was surprising was that they were not the same birds as the previous year – no bands! It makes me wonder how the Carolina Wren grapevine works.

Out and about in the winter woods, I often encounter Carolina Wrens at squirrel nests, both occupied and abandoned. I think they take shelter in the dense leaves, but I frequently also see them just rummaging around, energetically dismantling the nests, searching for whatever insects have also taken refuge in the wads of vegetation. This activity is usually accompanied by an assortment of babbling calls and mutterings. Best of all, even in the dead of winter, Carolina Wrens will burst into full song. It may be cold, and the sky might be gray, but that loud serenade spreads warmth and brightness through a whole dreary woodlot. Who doesn’t love that?

Tags: , ,
Posted in Uncategorized | 2 Comments »

« Older Entries
Newer Entries »