Wednesday, September 25, 2013

The Monarch Dethroned

I confess I have come to dislike the Monarch butterfly, Danaus plexippus, but it has nothing to do with the lovely insect itself. My objection is to the public obsession with the species to the exclusion of so many other butterfly species, let alone moths and other insects. It is also a manufactured obsession created by the many conservation groups that have capitalized on the Monarch’s existing popularity and used it to generate revenue for their organizations.

Let us explore some of the myths that have been purported as a result of the propaganda produced by the likes of Monarch Watch and the Xerces Society, whether accidental or intentional.

  • Monarch butterflies are important pollinators. The overwhelming majority of butterflies are poor pollinators. They belong in the category of “flower visitors” since their primary goal in alighting on blossoms is to obtain nectar, not pollen. Nectar is rich in carbohydrates that fuel the flight of many insects. Pollen, on the other hand, is rich in protein suitable for the growth of immature insects like bee larvae that have the chewing mouthparts to crack the pollen grains. Butterflies, with their siphoning mouthparts, cannot chew the grains, but the adult insects have little need for protein anyway. Bees, many moths, flies, certain wasps and beetles are far more important pollinators.

  • Genetically Modified Organisms (GMOs), especially crops, harm Monarchs. Monarch caterpillars feed only on milkweeds, so they are not coming into contact with genetically modified crops. There may be a grain of truth in suggesting that Roundup Ready crops immune to herbicides have led to a decline in milkweed plants in agricultural settings. Credit should go to Monarch Watch for promoting the cultivation of milkweeds in urban, suburban, and rural settings not subjected to herbicide use. There may be other reasons to dislike GMOs, but killing butterfly caterpillars is not one of them, at least in this case.
  • Monarch populations are crashing. Populations of many species of insects have boom and bust cycles, and I strongly suspect the Monarch is one of them. There is reason for concern regarding their wintering grounds in the mountains of Mexico, where illegal logging and irresponsible ecotourism definitely contribute to mortality of these insects. The adult butterflies are probably not very plastic in their ability to adapt to other potential wintering groves, if there are even any left standing. Once the butterflies nestle in for the winter, they are vulnerable to disturbances that startle them into flight and burn their fat reserves prematurely. Ecotour operators need to be evaluated to insure they are responsible in their visits to butterfly roosts.

    Still, conservation organizations may be guilty of creating a perpetual crisis that does not exist in reality. Were Monarch numbers declared stable, there would be no perceived endangered status, and monetary donations would dry up. This “sky is falling” phenomenon is probably true of many environmental organizations, and one should be wary when deciding where to spend one’s disposable income.

    All of this is not to say that the Xerces Society, Monarch Watch, and other non-profits are not doing valuable work, or are merely exploiting human sentiments for “poor butterflies.” Indeed, Xerces has branched out over recent years to address insect conservation beyond butterflies, such as protecting aquatic insects and native pollinators. Also, exaggerating an organism’s endangered status can be a way to draw attention to an otherwise overlooked or understated issue.

    The biggest problem I personally face in promoting insect conservation is in getting the public to think “outside the chrysalis” if you will, and recognize that arthropods other than butterflies are valuable. It is incredibly important to change public attitudes toward wasps, spiders, and flies, for example.

    We are making collective headway in creating popular movements that embrace dragonflies, damselflies, moths, and (to a lesser degree) tiger beetles, that do not involve collecting specimens. So, I remain cautiously optimistic that the trend will continue. Just don’t ask me about Monarchs.

  • Monday, September 9, 2013

    White-lined Sphinx ("Hummingbird Moth")

    Here it is, “Moth Monday,” and one species rises to the top of the priority list because it is experiencing a real population boom here on the Front Range in Colorado. The White-lined Sphinx, Hyles lineata, is common across most of North America, but in both the adult and larval stage it can make headlines and baffle the average citizen.

    Several species in the family Sphingidae go by the informal name of “hummingbird moth” because they approach or exceed the size of hummingbirds (wingspan 6.3-9 centimeters), and are frequently seen hovering in front of flowers like their namesake feathered friends. At first glance, many people believe they are indeed seeing a hummingbird. Then that long proboscis comes into focus. Out comes the smart phone or camera, and several Facebook posts later the person may finally get a proper identification.

    The adult moth can be active at almost any time of day or night, and visit a wide variety of flowers for the nectar they use to fuel their rapid, energetic flight. Below is a video I made of one of two specimens I saw in a butterfly garden in downtown Colorado Springs on August 30, 2013. I subsequently saw several more visiting an ornamental butterfly bush (Buddleja or Buddleia sp.) across the street from our townhouse….but they are everywhere right now, profiting from summer rains that made larval food plants available by the bushel.

    It is the caterpillar stage that often causes people consternation. They superficially resemble the tomato hornworm, but are more conspicuous and often more numerous. The image below depicts the typical appearance, but the larvae can be yellow, or mostly black, with much variation in between.

    The caterpillars are general feeders on a variety of plants, shrubs, and trees, but seem partial to those in the evening primrose family. Oenothera primrose plants are not terribly substantial, so it takes more than one plant for a caterpillar to mature. The larva simply finishes off one plant and walks on to another. When there are lots of caterpillars (one female moth can lay up to 500 eggs), food plants can quickly become scarce as they are consumed, and the caterpillars are forced to “march” in search of literally greener pastures. These large scale “migrations” may cross rural roads creating a slick hazard as they are crushed under tires.

    Once finished feeding, the caterpillar again begins walking in search of a place to pupate. Each larva burrows into the soil and creates a chamber several inches underground. There it molts into the pupa stage. This is how the species overwinters, though there is usually more than one generation per year, especially under favorable conditions.

    The White-lined Sphinx also ranges south to Argentina. A very similar species, Hyles livornica occurs in Eurasia and Africa, and may account for persistent claims that H. lineata is found in the Old World.

    Look for the adult moths at dusk and dawn, for they are mostly crepuscular in their activities. Still, they may show up at your porch light after dark as well. By day they usually hide among tangled grasses where the moth’s pattern of lines serves it well as camouflage.

    This is an animal of open habitats, so they are most abundant in prairies, deserts, agricultural lands, vacant lots, and gardens. In the western U.S., the White-lined Sphinx is a resident species only from southern California to west Texas. It immigrates annually farther north. Rarely is this moth a pest, though the caterpillars occasionally do damage to grapes and tomatoes in Utah.

    Hyles lineata, as prolific as it is, is not without enemies. Pallid bats and large mantids eat the adult moths. Tachinid flies in the genera Belvosia, Drino, Winthemia, and Compsilura among others, are internal parasites of the caterpillars. Certainly ichneumon wasps and braconid wasps are also parasites.

    Sources: Arnaud, Paul Henry. 1978. Host Parasite Catalog of North American Tachinidae (Diptera). Washington, DC: U.S. Department of Agriculture, Miscellaneous Publication No. 1319. 860 pp.
    Oehlke, Bill. 2001. Sphingidae of the Americas.
    Opler, Paul A., Kelly Lotts, and Thomas Naberhaus (Coordinators). 2013. Butterflies and Moths of North America.

    Thursday, September 5, 2013

    Caught on Video: Prionyx atratus

    I have been neglectful in exploiting my camera’s ability to shoot video as well as still images, until this year. I use a Canon PowerShot SX10 IS, and it does a nice job delivering the quality still images you see here on my blog. I am surprised by the detail I can get in video, too, perfect for documenting insects in action, with all their odd behaviors. One of my first subjects was a thread-waisted wasp, Prionyx atratus. Actually, I know I took video of at least two different females, both in the process of stocking their underground burrows with paralyzed grasshoppers.

    July 16, 2013 was, for whatever reason, my lucky day to find several wasps engaged in nesting behavior. Up the street from our townhouse here in Colorado Springs is a vast open area cut by Sand Creek, a mostly dry riverbed or “arroyo,” and the surrounding soil is likewise sandy and very hospitable to burrowing insects of all sorts. Many “social trails” weave throughout the vacant, degraded shortgrass prairie, and it was in these trails that Prionyx atratus were nesting.

    Normally, wasps resting on the ground are quick to fly far away at your approach, so I was confused as to why this one wasp was not eager to make an exit. Instead, it was persistent in running around my feet. I backed off and noticed freshly-excavated sand at the mouth of a small hole. I watched, and sure enough, the female wasp made her way back to her construction site. I shot many still pictures before I even thought to try video, so she was nearly finished opening the nest when I shot the following clip.

    Notice how she “pulls” loads of soil out of the burrow, using her front legs. This is in contrast to other wasps that actively kick sand out behind them (Bembix “sand wasps” for example).

    Prionyx atratus, like most members of the genus, dig nest burrows after obtaining prey. After securing prey, they leave their paralyzed victim a good distance away from where they begin digging, perhaps minimizing the opportunity for parasites like the tiny “satellite flies” you can see in the video that stake out a nest and wait for an opportunity to lay their own eggs (satellite flies actually “larviposit,” laying tiny, live larvae) on the wasp’s prey.

    What surprised me was the speed with which the wasp retrieved her prey and hauled it head first down into the nest. I only managed this still shot.

    Later, I came across a second wasp, and this time I did manage to capture her retrieving her prey. She still nearly outran my ability to keep up with her through the lens. Keep in mind, too, that grasshoppers are not lightweight insects. She has no problem trucking the creature overland despite its size and weight. I imagine that feat would be comparable to a human carrying a sofa in their arms and teeth, holding the couch out in front of them. And then running with it.

    Prionyx closes her nest as carefully as she digs it, packing the loose soil into the tunnel for at least a centimeter, then obliterating all evidence of her labors on the surface before flying off to start another nest elsewhere. Here is a short clip of the closing process.

    This species is a stocky animal not easily confused with similar wasps given a good look. The body is relatively short, the abdomen not extending beyond the wingtips when the wasp is at rest. The legs are relatively short and very spiny, more so than in other sphecid wasps. The abdomen is nearly spherical, not oval or elongate like most other wasps. This species is entirely black, females with silvery or gold faces, owing to appressed, reflective scales. Females average 15 millimeters in body length, males 12 millimeters. Their stocky form makes the look substantially larger.

    Look for this insect across virtually the entire U.S. and southwest Canada (British Columbia and Saskatchewan near the border). Take heed if a wasp sticks around in your presence, she may have a burrow close by.

    Sources: Bohart, R.M. and A.S. Menke. 1976. Sphecid Wasps of the World. Berkeley: University of California Press. 695 pp.
    Pickering, John, et al. 2013. Discover Life.

    Sunday, September 1, 2013

    Arrowshaped Micrathena spider

    It must be a banner year for spiders in southern Ohio. We saw large numbers and quite a diversity of orbweavers alone on our recent trip to Cincinnati and Adams County, August 18-26. Among the more remarkable species was the Arrowshaped Micrathena, Micrathena sagittata. We found several individual females on the trail to Buzzardroost Rock, a preserve managed by The Nature Conservancy in Adams County near the town of Lynx.

    The spiny orbweavers, which includes the genera Micrathena and Gasteracantha, are mostly tropical, and some species in the rainforests of southeast Asia, Australia, and Africa are even more extreme in the spikes, horns, and other processes jutting out of their armored abdomens. No doubt a spider studded in spines is not terribly appetizing to a predator.

    The Arrowshaped Micrathena is not a particularly large spider, ranging from 8-9 millimeters in body length for mature females to only 4-5 millimeters in males. Males are seen less frequently than females by the casual observer and they lack the spines that adorn their mates. The color and pattern of this species is relatively consistent, as shown in these images.

    Looking at the underside of the spider, we see that her spinnerets are located in the center of her abdomen, rather than at the posterior where you would expect them to be. Her venter (underside) is mottled black or brown and yellow, which helps camouflage her from predators that might approach from overhead.

    The spiders spin circular webs about one foot in diameter with a tight spiral and an open hub (center). The spider hangs onto the threads that frame the hub, and also secures herself to the hub with strands of silk issuing from her spinnerets. She can drop out of the web and into the leaf litter below if she feels threatened, but then reel herself back to the hub when danger passes. A zigzag band of silk called a “stabilimentum” may be present, if only vaguely, immediately above the center of the web. The function of this decoration is still debated, with theories ranging from it representing a fake flower to attract insect prey, to a way to advertise to birds that a web obstructs their flight path.

    The web is usually tilted somewhere between the vertical and horizontal planes, which makes it challenging to get decent images of the architect sitting on it. The abdomen of the spider may also sag, so getting the whole animal in focus is problematic. The spiders usually build their webs in shrubs and among other plants in the understory of deciduous forests, or along forest edges and openings in the canopy. Look for them two to four feet off the ground. They aren’t easy to spot even then. Researchers in Kansas found the webs particularly common in stands of Green Dragon (Arisaema dracontium), Pennsylvania Pellitory (Parietaria pensylvanica), and American Lopseed (Phryma leptostachya).

    The snare intercepts flying and jumping insects, like leafhoppers, that the spider then feeds on. Interestingly, these spiders do not wrap their prey as other web-builders do. Flies, small wasps and bees, and beetles have also been recorded as prey of this spider.

    Mated, mature females construct fluffy, spherical egg sacs of white silk, about 12 millimeters in diameter and containing roughly 90 eggs. The egg sac is the overwintering stage and mature spiders are seen mostly from July to September.

    Micrathena sagittata is found from Maine to Florida and west to Nebraska and Texas, but is probably more common in the southern portion of its range.

    Right now is prime spider-hunting season, with webs becoming more obvious as the spiders reach maturity, and leaves start to fall during autumn. Enjoy looking for them.

    Sources: Bradley, Richard A. 2013. Common Spiders of North America. Berkeley, California: University of California Press. 271 pp.
    Fitch, Henry S. 1963. Spiders of the University of Kansas Natural History Reservation and Rockefeller Experimental Tract. Lawrence, Kansas: University of Kansas Museum of Natural History, Miscellaneus Publication No. 33. 202 pp.
    Howell, W. Mike and Ronald L. Jenkins. 2004. Spiders of the Eastern United States: A Photographic Guide. Boston, Massachusetts: Pearson Education. 362 pp.
    Jackman, John A. 1997. A Field Guide to Spiders & Scorpions of Texas. Houston, Texas: Gulf Publishing Company. 201 pp.
    Kaston, B.J. 1972. How to Know the Spiders (Third Ed.). Dubuque, Iowa: Wm. C. Brown Company Publishers. 272 pp.