Friday, April 18, 2014

Mourning Cloak

I have neglected butterflies on this blog for the most part, as there are plenty of other blogs about them, books and websites, too. Plus, let’s face it: they are easy to love. My general mission is to stir a passion for other insects and invertebrates. That said, at this time of year along the Front Range of Colorado, certain butterflies are the most obvious of insects. The Mourning Cloak, Nymphalis antiopa, is also admirable for its sheer durability.

This butterfly is one of the “tortoiseshell” butterflies, a subgroup of the family Nymphalidae, collectively known as “brushfoots.” Look at any nymphalid and it looks like the insect has only four legs instead of the customary six. The front legs are greatly reduced in size and drawn up close to the head, where they function more like extra mouthparts than legs. The female butterfly scratches leaves with those tiny legs, causing the plant to produce volatile compounds that the butterfly analyzes to make sure it is a proper host plant on which to lay her eggs.

Tortoiseshell butterflies overwinter as adult insects, crawling into crevices and cavities in logs, stumps, and other protected spots. A warm winter’s day will see them taking wing, before going back into hiding until early spring.

Once a Mourning Cloak emerges from hibernation, it seeks sustenance to fuel its flights. A favorite source of nourishment is sap oozing from wounded trees. Indeed, a sap flux can quickly become a mecca for these butterflies, as evidenced in the short video below. They are amazingly tolerant of each other’s company considering their usual behavior.

Male tortoiseshell butterflies are highly territorial, each one staking out a patch of real estate that it defends vigorously from other males, and even from other species. I say many a battle between a male Mourning Cloak and a male Hoary Comma on April 11, the day I shot most of these images along a riparian trail near the Bear Creek Nature Center in Colorado Springs. The insects would often literally bang into each other during their aerial dogfights.

While males quickly become tattered and exhausted, females, once mated, set about to find suitable host plants on which to lay eggs. You will find the Mourning Cloak to be most abundant in willow thickets, as Salix spp. are the favored hosts. Caterpillars will also feed on elm, birch, poplar, hackberry, rose, mulberry, and other trees and shrubs to a lesser degree.

Large masses of eggs, typically 100-200, are laid by the female, the ova encircling a branch or twig. The caterpillars pass through five instars (an instar is the interval between molts), eventually topping out at about 5 centimeters (two inches) in length. Black with white speckles and maroon spots, the larvae are studded with spikes.

They occur in large groups, so when you find one you will usually find several more nearby. During their younger instars they share a loose, tent-like web for protection from predators and parasites.

By June or July another generation of Mourning Cloaks is on the wing. There may be two generations in the southern reaches of this butterfly’s range, but at higher elevations and latitudes there is but one generation produced each year, fresh adults emerging in late August or early September.

The Mourning Cloak is holarctic, meaning it is found throughout the northern hemisphere. In Britain it is known as the “Camberwell Beauty.” Here in North America, it ranges from Alaska to Mexico, and the Pacific Coast to the Atlantic seaboard.

Few insects live as long as a Mourning Cloak in the adult stage. On average, they survive 10-11 months, though much of that is sequestered in a hibernaculum. They are always a welcome sight, and a true harbinger of spring if ever there was one.

Sources: Brock, Jim P. and Kenn Kaufman. 2003. Kaufman Field Guide to Butterflies of North America. Boston: Houghton Mifflin Co. 384 pp.
Ferris, Clifford D. and F. Martin Brown. 1980. Butterflies of the Rocky Mountain States. Norman: University of Oklahoma Press. 442 pp.
Pyle, Robert M. 2002. The Butterflies of Cascadia. Seattle: Seattle Audubon Society. 420 pp.

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.