Wednesday, February 10, 2016

Tiny Wasp Hero Slays Redback Spiders in Australia

Spider wasps in the family Pompilidae are fearless hunters of arachnids as small as jumping spiders and as large as tarantulas (the "tarantula hawk" wasps), but I was unfamiliar with any species of pompilid going after cobweb weavers in the family Theridiidae. That was until late last week when these stunning images came across my Facebook news feed.

Abel González snapped these images of a female Agenioideus nigricornis spider wasp carting a paralyzed Redback Spider, Latrodectus hasselti, back to a nest burrow in Oldbury, Western Australia. The significance of this behavior requires a bit of backstory.

The Redback Spider is one of the most dangerously venomous arachnids in Australia. Indeed, it is in the same genus as the widow spiders of North America: Latrodectus. Any organism that targets such a potentially lethal animal deserves some acclaim. Oddly, we have species of the wasp genus Agenioideus here in the U.S. as well. I witnessed a female A. humilis hauling a comatose orb weaver here in Colorado Springs last year, and even posted about it, complete with video, in this blog entry. Our New World species do not go after cobweb weavers, let alone widows.

The initial discovery of the relationship between the Australian A. nigricornis and the Redback Spider is credited to a nine year-old boy, who spotted a wasp dragging a spider in his backyard in Beaconsfield, Western Australia. The young lad pointed out the drama to his father, who was astute enough to collect the two animals and photograph the habitat. The specimens eventually crossed the desk of Andy Austin, a professor at the University of Adelaide, who identified them.

This is not a big wasp. Females are only 8.24-13.11 millimeters in body length. Perhaps their diminutive size helps them navigate the labyrinth that is a Redback Spider's web. It is apparently still a mystery how the wasp manages to subdue its prey to begin with.

Back here in the U.S., the only spider wasp thought to be a potential predator of widows is Tastiotenia festiva, based on one circumstantial record from Rodeo, New Mexico. The range of T. festiva is restricted to the extreme southwestern U.S. One other wasp is very well known as a predator of widows. It is the Blue Mud Dauber, Chalybion californicum, a very widespread member of the family Sphecidae.

The Australian wasp was known to science as far back as 1775, when it was first described from specimens collected by Captain James Cook in 1768; and it is a common insect found throughout Australia. The fact that its host was unknown until the 21st century speaks to how much we have yet to learn about even the most familiar of invertebrates.

Sources: Krogmann, Lars, and Andrew D. Austin. 2012. "Systematics of Australian Agenioideus Ashmead (Hymenoptera: Pompilidae) with the first record of a spider wasp parasitizing Latrodectus hasselti Thorell (redback spider)," J. Aust. Entomol. Soc. 51: 166-174.
Staff. 2012. "Killer Spider Meets Its Match in Tiny Wasp," LiveScience.
Wasbauer, M.S. and L.S. Kimsey. 1985. "California Spider Wasps of the Subfamily Pompilinae," Bulletin of the California Insect Survey. Vol. 26: 1-130.

Thursday, February 4, 2016

Book Review: The Bees in Your Backyard

The digital age has thankfully produced a wealth of resources, both online and in print, for amateur naturalists looking for information about insect pollinators. Perhaps the best of these to date is The Bees in Your Backyard, by Joseph S. Wilson and Olivia Messinger Carril (Princeton, NJ: Princeton University Press, 2016). This is a visually-rich, up-to-date reference to all the genera of bees in North America north of Mexico.

At eight-by-ten inches in size, this book really isn't a field guide, but a useful tool to help determine the identity of an individual bee from a specimen or detailed image. As one becomes more familiar with key characters of different kinds of bees, they become increasingly easier to identify in the field.

The Bees in Your Backyard could be recommended simply on the strength of the "keys" it employs to aid in bee identification, but it goes beyond that. The discussion of each genus includes distribution maps that show not only where those particular bees occur, but their level of abundance and diversity in a given area. There are also graphs showing the seasonal distribution of the bee genus; and a scale with life-size silhouettes shows the size range of the genus.

As the average infomercial goes "but wait, there's more!" Indeed, the introductory pages address bee anatomy, bee biology, how to study bees, and a key to the different families of bees. A separate chapter gives tips on how to promote bee diversity in your yard, garden, and neighborhood.

Interesting and relevant facts are scattered throughout the book in highlighted boxes of text. These are welcome little "surprises" and bonuses, but sometimes become distracting.

If there is any complaint with the book it may lie in this "busy" appearance. People who have a difficult time with their attention span or ability to focus may have problems with the book's organization. For example, chapters are divided into sections with decimal numbers (chapter 1 is divided into 1.1, 1.2, 1.3, etc). This is reminiscent of a textbook or website presentation and thus may appeal to students but not an older, more informal audience. Page numbers are located in the middle of the side margins of each page, and I, for one, have to learn that all over again each time I open the book.

Until now, the best reference for bee identification for this region was The Bee Genera of North and Central America, a bilingual (English-Spanish), scholarly work by Charles D. Michener, Ronald J. McGinley, and Bryan N. Danforth (Washington, DC: Smithsonian Institution Press, 1994). That book is now very much outdated, and is exceedingly expensive. Information on the biology of the bees is also minimal.

Whatever its minor shortcomings, or differing reader preferences, The Bees in Your Backyard is by far your best bet for a comprehensive work on all things apoid, in a compact 288 pages, too. Plus, at $29.95 U.S., it is highly affordable. Make sure you add this to your library, and use it often. Pollinators need all the help they can get, especially our native, solitary bees.

Tuesday, February 2, 2016

Damsels That Cause Distress

Note: The subject for this post was requested by one of my followers. You, too, are welcome to make requests for subjects or topics. Simply e-mail: bugeric247ATgmailDOTcom.

Nabis sp. from Colorado

You would think that insects called "damsel bugs" would be delicate and and otherwise dainty. Well, many members of the true bug family Nabidae are delicate, and certainly small, there is nothing meek about them. They are mostly nocturnal predators that can subdue other insects even larger than themselves.

Hoplistoscelis pallescens, Massachusetts

There are nine genera and 41 species of damsel bugs in North America north of Mexico. None of them are greater than 12 millimeters in length as adults, most of them smaller than that.

Nabis sp. from Colorado

The femur segment of the front leg is usually muscular and swollen, armed with at least one row of small teeth on the underside. This helps the insect to secure prey.

Some nabids are wingless when mature, or have forms with abbreviated and useless wings. Those that fly are often attracted to lights at night, perhaps to prey on other insects drawn there.

While I was in Massachusetts in 2009, I witnessed a specimen of Nabis roseipennis stalk and assassinate a small braconid wasp. The persistence and fearlessness of the little true bug was impressive.

Nabids are easily mistaken for other kinds of true bugs, and it takes a bit of practice to recognize them. Most assassin bugs (Reduviidae) are larger, but they and damsel bugs both have a short rostrum ("beak") compared to most plant-feeding true bugs.

Plant bugs in the family Miridae are perhaps the most similar to damsel bugs, but mirids have a "cuneus," a pronounced wrinkle or notch in the margin of the front wing near where the leathery portion meets the membrane near the tip. Damsel bugs lack this feature.

Here in Colorado, one of our common damsel bugs is a small, dark, ground-dwelling member of the genus Pagasa. They are almost beetle-like in appearance, and I have mistaken more than one for a ground beetle as it ran across the path in front of me. Pagasa can be fully-winged or have wings reduced to non-functional pads.

Pagasa sp., Colorado

The tip of the tibia on the front leg of Pagasafeatures a specialized pad of hairs called the fossa spongiosa that aids them in climbing slick surfaces and grabbing slippery prey.

Pagasa sp., Colorado

So effective are damsel bugs as predators that they are considered economically important as pest control in agricultural systems. Indeed, they are also among the most abundant of small predators.

Nabis capsiformis from south Texas

Sources: Henry, Thomas J., and Richard C. Froeschner. 1988. Catalog of the Heteroptera, or True Bugs, of Canada and the Continental United States. New York: E.J. Brill. 958 pp.
Kerzhner, Izyaslav M., and Thomas J. Henry. 2008. "Three new species, notes and new records of poorly known species, and an updated checklist for the North American Nabidae (Hemiptera: Heteroptera)," Proc. Entomol. Soc. Wash. 110(4): 988-1011.
Slater, J.A. and R.M. Baranowski. 1978. How to Know the True Bugs. Dubuque, Iowa: Wm. C. Brown Company Publishers. 256 pp.

Friday, January 29, 2016

The Stable Fly

Of all the biting flies we have in North America, one of the most annoying has to be the Stable Fly, Stomoxys calcitrans. They are especially abundant around farms, ranches, zoos, and other places where large mammals are kept. Unfortunately, they will also bite people when livestock is not close at hand.

Like any notorious villain worth their salt, the Stable Fly has it aliases: "beach fly," "dog fly," and "lawn-mower fly" among them. The insect has also fled local jurisdiction. It is apparently native to Eurasia and Africa, with speculation that it probably came to the New World in colonial times, maybe in ship's ballast.

The Stable Fly is easily dismissed as a House Fly under cursory examination. Both flies are in the family Muscidae; and both are about the same size, the Stable Fly measuring 5-7 millimeters. Each species is mostly gray, with black "pinstripes" down the back of the thorax. The Stable Fly differs mostly in having a slender, black, slightly curved beak tucked under its "chin."

Proboscis (painfully) deployed!

While it is only the female mosquito, black fly, deer fly, and horse fly that sucks blood, both genders of the Stable Fly can bite. This is not a painless event, either. An immediate, sharp sensation occurs when the fly plunges its piercing mouthparts into your skin. Shoo it away and it returns instantly, and repeatedly. This persistence is perhaps the main source of our aggravation.

Commencing feeding
Almost full!

The adult fly is only one quarter of the life history of the species of course, with eggs, larvae, and pupae making up the other three stages in its metamorphosis. The female fly deposits her eggs singly, or in clusters of 25-30, in wet, decaying fibrous organic matter. Typical breeding material includes horse manure, silage, rotting hay, grass clippings, and partially composted livestock bedding.

Female full of eggs

The eggs hatch in one to fourteen days. The maggots that emerge take anywhere from 11-30 days on average to mature. The interval is largely determined by temperature, humidity, and food quality and quantity. The hotter and more humid the substrate, the faster the maggots develop. The maggot molts twice after hatching, and may be up to twelve millimeters in length by the time it enters the pupal stage.

The pupa represents the larva's third molt, the shed exoskeleton of which forms a hard, oval, dark brown "capsule" around the pupa itself. The pupal stage typically lasts six to twenty days. The adult fly then bursts out of its capsule by more or less inflating the front of its head.

Stable Flies will also sip flower nectar

The determination of Stable Flies in their feeding behavior naturally induces stress in its victims, and this can take a toll on livestock. A mere twenty flies on a cow can result in decreased milk production. Mild anemia and weight loss can also be a result of high numbers of feeding Stable Flies.

Were it such that general malaise was the only negative effect of Stable Fly populations, it would possibly be tolerable. Unfortunately, Stomoxys calictrans can also carry a variety of diseases. Most of these are of limited effect in the U.S., thankfully, but they cannot be dismissed entirely. Here, the fly can transmit anthrax, which affects livestock, pets, and people. Anthrax exhibits a variety of symptoms, the worst of which include lesions of the lungs or brain.

The next time you visit a local farm, ranch, or zoo, you might want to consider applying that DEET-based insect repellent to help fend-off attacks of Stable Flies. It will make your experience much more enjoyable if it is bite-free.

Sources: Cumming, Jeffrey M. 2006. "Diptera Associated With Livestock Dung," North American Dipterists Society.
Newberry, J. 2003. "Stomoxys calcitrans" (online), Animal Diversity Web.