Friday, April 11, 2014

Beetles from Bones

This past Wednesday, April 9, I went exploring near my home to see what insects are out and about here in Colorado Springs this spring. In my wanderings I stumbled upon a few bones of some large mammal, providing an opportunity to find insects specific to carrion.

I am not terribly keen on handling carcasses, but these leg bones were mostly dry. The ligaments were still intact on one leg, but flies had long lost interest in these remains. Still, it takes little to attract ants, and some kinds of beetles. I managed to find three species large enough for photos, plus a couple very tiny rove beetles (family Staphylinidae) that quickly vanished when I turned over the bones.

The first insect I saw was, oddly, a Small Milkweed Bug, Lygaeus kalmia. Many normally herbivorous Hemiptera are opportunistic scavengers, though, so perhaps the appearance of this insect should not have been terribly surprising. The second insect was one I expected, and present in fair numbers considering the relative size of the carcass: Common Carrion Beetles, Dermestes marmoratus.

Dermestid beetle and Small Milkweed Bug

Dermestids are so efficient at scouring the last vestiges of flesh from bone that natural history museums employ colonies of the beetles to clean skeletons. This particular species, a relative of that indoor pantry pest the Larder Beetle, is a handsome insect measuring 10-13 millimeters. The silvery-gray scales on its otherwise black body make it look quite dapper considering the situations it frequents. D. marmoratus is found from southern California through the southwest, southern Rocky Mountains, and Great Plains states.

Dermestes marmoratus

The most spectacular specimen uncovered was a Northern Carrion Beetle, Thanatophilus lapponicus, also known as the Silky Carrion Beetle. It looks superficially like a giant dermestid, 8-15 millimeters in length, but it belongs to an entirely different family, the Silphidae. This species is holarctic, meaning it ranges across the entire northern hemisphere. In North America it is found in Alaska, Canada, and the northern tier of states in the U.S., plus the Pacific states to Baja, Mexico, and the Rocky Mountain states. The adult beetles have been found from March to October. Perhaps its hairy body helps to insulate it against cooler temperatures.

Thanatophilus lapponicus

The last beetle species I collected was a type of sap-feeding beetle in the family Nitidulidae. At only 3-5 millimeters, Nitidula ziczac is difficult to spot, let alone get a clear image of. Despite their name, sap-feeding beetles are highly diverse in their appetites. Some species are found in abundance inside yucca flowers, for example. N. ziczac is a well-known associate of carrion, found in North America mostly from the Great Plains westward, as near as I can tell from various references.

Nitidula ziczac

What truly amazes me about carrion-inhabiting insects is how they manage to locate such a scarce resource. They need the energy to fly to far-flung bodies, at just the right time. Certainly their olfactory powers are light years ahead of us humans (I detected absolutely no odor from these particular bones), and tuned specifically to aromatic compounds liberated during decomposition. However they do it, thank goodness they do, or we would be forever tripping over dead animals, before becoming deathly ill ourselves.

Source: Evans, Arthur V. and James N. Hogue. 2006. Field Guide to Beetles of California. Berkeley: University of California Press. 336 pp.

Tuesday, April 8, 2014

The Bagrada Bug

California and Arizona have an immigration problem. No, not those immigrants; I am referring to an insect known as the Bagrada Bug, Bagrada hilaris. This member of the stink bug family Pentatomidae is native to Africa but has found its way to the U.S. where it has quickly become a crop pest. It is also known as the "Painted Bug."

The Bagrada Bug has not been here long. It was first detected in June of 2008 in Los Angeles County, but is now found abundantly throughout southern California and adjacent southern Arizona, eastward through southern New Mexico and into Texas. It had previously established itself in Italy, Malta, and southern Asia.

This insect is frequently mistaken for the native “Harlequin Bug,” Murgantia histrionic, but the Bagrada Bug is about half the size of its native cousin, adults measuring a mere 5-7 millimeters.

Murgantia histrionica, the "Harlequin Bug"

The nymphs of B. hilaris are occasionally dismissed as beneficial lady beetles due to their bright red and black markings. There are five nymphal instars, an “instar” being the interval between molts.

Bagrada hilaris nymph

What makes the Bagrada Bug problematic is its appetite for plants in the cabbage and mustard family (Brassicaceae in today’s classification, Cruciferae of previous eras). So, kale, turnips, broccoli, radishes, and related vegetables are all on its menu. It doesn’t end there, either. The bug is also known to feed on potato, sorghum, cotton, papaya, maize, various legumes, and other crops. Ornamental plants like sweet alyssum and candytuft are also vulnerable.

The appearance of this pest in the U.S. caught everyone off guard, including entomologists. Its biology and natural enemies are barely known, so few control methods can be applied, let alone biocontrol agents like parasites and predators. We don’t even know exactly how fast the Bagrada Bug is spreading.

You can help improve our understanding of the distribution of B. hilaris by keeping an eye out for it and reporting your observations to your state department of agriculture. Having images to back up your identification can help immensely.

Almost all information on the Bagrada Bug in the U.S. is found online because the species is such a recent introduction here. The most trusted resources are websites with URL addresses ending in “.edu” or “.gov.” Commercial sources are often less accurate.

Sources: Arakelian, Gevork. 2013. “Bagrada Bug,” Center for Invasive Species Research, University of California, Riverside.
Flint, Mary Louise, et al. 2013. “Pest Alert! Bagrada Bug,” UC IPM Online, University of California.
Wisch, Hartmut, et al. 2012. “Species Bagrada hilaris - Bagrada Bug,” Bugguide.net.

Sunday, April 6, 2014

Sheetweb weaver, Drapetisca alteranda

I was fortunate enough to find many interesting insects and spiders while living in South Deerfield, Massachusetts in 2009. One nice surprise was stumbling upon a specimen of the sheetweb weaver Drapetisca alteranda. Not only is this spider quite small (females are only 4-4.5 millimeters in body length), but it is exceedingly well camouflaged. Oh, and nocturnal, too.

This spider is atypical of the family Linyphiidae and can be easily mistaken for something like a lynx spider or other hunting spider that does not spin a web, but waits in ambush instead. Drapetisca lives on tree trunks where it sits motionless. Close inspection reveals that it is actually not in contact with the surface of the tree, but sprawling across the thinnest of snares.

It was by sheer luck that I noticed the specimen imaged above. I was seeking insects and arachnids around a bright light outside the town library the night of July 30. The light illuminated not only the exterior of the library, but a nearby tree as well. Ants, beetles, and other insects paraded up and down the trunk, and I found at least one Common House Spider in her snare under a branch. My flashlight eventually revealed the Drapetisca at roughly shoulder height, much to my surprise and delight.

Male specimen, © Tom Murray via Bugguide.net

This spider is, unfortunately, best identified by characters that are not easily observed in the field. The jaws are armed with a set of three or four long spines that criss-cross (see image below). The female’s external genitalia (epigynum) are also diagnostic, but that necessitates turning the spider over and putting her under a microscope. Still, the overall appearance of the spider, and its posture on its web, help to eliminate other potential suspects.

© Charley Eiseman, "Bug Tracks" blog

As is the case with most organisms that are of no economic importance, precious little is known of this spider’s biology and distribution. It appears limited in its range to southern Canada and the extreme northern U.S. It is common in New England, and recorded from the Great Lakes region, Montana, Alberta, and British Columbia. It may be absent from the northern plains.

Female with egg sac, © Kyron Basu via Bugguide.net

Your own persistence and patience in seeking spiders like this one could reveal much new information. Nothing ventured, nothing gained, so do share your own images and observations.

Sources: Eiseman, Charley. 2011. “Kleptoparasite,” Bug Tracks blog.
Hollenbeck, Jeff. 2006. “Species Drapetisca alteranda,” Bugguide.net
Kaston, B.J. 1978. How to Know the Spiders (3rd Ed.). Dubuque, Iowa: Wm. C. Brown Company Publishers. 272 pp.

Friday, April 4, 2014

Cow Path Tiger Beetle

One of the few insects to have poked its head out while we still have the threat of snow here on the Front Range of Colorado is the Cow Path Tiger Beetle, Cicindela purpurea. Also known as the “Purple Tiger Beetle,” it seems to come in just about every color except purple. Whatever its wardrobe, it is a welcome sight and a challenging subject to stalk and photograph, whether here or elsewhere on the continent.

© Heidi Eaton

Tiger beetles in North America typically have one of two emergence patterns. Some have a two-generation spring/fall cycle whereby the adult beetles are present in those two seasons. Others have one generation seen only in summer. Many species also have specific habitat requirements, making them hard to find in the first place. Then there is the fact that if they aren’t moving, you have a hard time seeing them.

These beetles also earn their name: they are efficient predators of many other insects, even ants. They have reasonably keen vision and run swiftly, like diminutive cheetahs. They run so fast, in fact, that they can literally outrun their eyesight. When sprinting after a potential meal, they go blind, and must stop to re-focus. This run, stop, run behavior helps to identify them in the field. Get too close to one and it will fly, usually a short distance, land, and resume its darting gait.

Tiger beetle larvae are also predatory. Each lives in a (usually) vertical burrow just wide enough to accommodate the grub. A hump midway down its body, armed with hooks, anchors the larva against one wall. The overall appearance of the grub is an “S” shape. The flattened head of the larva is flush with the rim of its tunnel as it lies in wait for a hapless insect to blunder by. It then lunges with lightning speed, grabbing the victim in its jaws. When disturbed, a tiger beetle larva rapidly descends deep into its lair.

Adult Cow Path Tiger Beetles measure 12-16 millimeters and may be matte green, metallic green, bluish, black, or bronze-purple with green highlights. The species has been divided into named “races” based on these differences. Most have consistent ivory markings: a spot at the tip of each elytron (wing cover), and a mark that looks like an oblique tilde symbol (“~”). There may or may not be an additional spot near the edge of the elytron between the squiggle and the terminal spot.

It is not unusual to find two different color morphs to be mating, as shown here. They recognize each other by the dimples in the female’s thorax, which fit the teeth on the male’s jaws like a lock and key. Attempted mating by the male of another species would be futile, as his jaws would slip off her thorax.

Look for these lovely beetles in degraded prairie habitats, where there is sparse grass and plenty of bare patches of earth. They are not often found in large numbers, and while much of a given landscape may look to us to be hospitable to them, they can be sporadic at best.

The good news is that Cicindela purpurea is a very widespread species found over most of the northern three-fourths of the U.S., plus adjacent southern Canada. It is largely absent from the mid-Atlantic states, southeast, Texas, and coastal areas of the Pacific states. April, May, and September are the months this species is most abundant. Keep in mind that some years they might emerge earlier or later, depending on how mild the winter is.

Sources: Acorn, John. 2001. Tiger Beetles of Alberta: Killers on the Clay, Stalkers on the Sand. Edmonton: University of Alberta Press. 120 pp.
MacRae, Ted. 2011. “Monroe Canyon epilogue – Audubon’s tiger beetle,” Beetles in the Bush.
Anonymous. 2005. “Cow Path Tiger Beetle,” Tiger Beetles of Nebraska.