The Nature Writers of Texas

The best nature writing from the newspaper, magazine, blog and book authors of the Lone Star State . . .

Sunday, August 20, 2006

Eurasian Collared-Doves Continue to Spread
by Ro Wauer

The rapidly increasing population of Eurasian collared-doves became a strong reality for me recently when two of these large doves suddenly appeared in my backyard, representing bird number 176 for my yard. In March 1998, when I wrote a nature note about a small population at Six Mile, near Port Lavaca, that was the first time that I had actually seen this newcomer in our area. But almost the same time they began to appear in numerous other places in our region, such as Tivoli, Galveston, and High Island. But soon after that they could be found almost everywhere in towns along the Gulf Coast, and now they can be found throughout the state, from the Lower Rio Grande Valley to the Panhandle and westward to El Paso.

The rapid spread of this dove all across the United States is truly unusual. It apparently arrived in South Florida in 1987, after 50 individuals escaped from a breeder’s aviary in the Bahamas in 1974. It is native to India, but was introduced into Hungary in the mid-1800s and had spread all across Europe and to Great Britain by the 1950s. Soon after the reports from Florida, there were additional East Coast reports from as far north as Nova Scotia, Canada. And soon after that it was reported from Utah and Montana.

It is fascinating to be able to follow a bird's "natural invasion" across the continent. Our abundant cattle egret is an earlier example of such an invasion from an Old World species. These white, grassland birds appeared in Central America during the 1930s, moved north into Florida by 1948, and are now found throughout North America, at least in summer. And a few cattle egrets are resident along the Central Gulf Coastal Area year-round.

It will be very interesting to assess whether or not increasing collared-dove populations have any influence on the longtime resident doves. It is unlikely that the increase in collared-doves will affect the smaller doves - Inca and common ground-doves - but populations of mourning and white-winged doves may decline. Texas Parks and Wildlife biologists are currently studying this topic. The increase of collared-doves eventually may also add another game bird to the list of huntable Texas species.

The two collared-doves that appeared in my yard began feeding alongside the Inca and white-winged doves that already were present when they arrived. They walked around the yard for a brief time, sampling some of the seed, and then just as suddenly flew away. I have not seen then since. However, just like my first white-winged dove sightings a few years ago, that included one or two visitors at a time, they soon learned where they could find a handout. And now white-wings are a daily feeder; as many as eight or ten can be present at once. And since they can clean out a feeder in a very short time, I have started to use feeders with smaller perches so that these really large birds must settle for finding seed on the ground below the hanging feeders. That works reasonably well.

The increase in the numbers of birds that expect a handout on a regular basis is not for the best, although I still want to feed my smaller regulars, such as cardinals, chickadees, and titmice. And posting "big birds are not welcome" signs won't work. Maybe I will cut way back on the feeders and continue to attract birds primarily with water. My three birdbaths are as popular as ever!

Sunday, August 13, 2006

Parasitic Wasps Are Widespread
by Ro Wauer

Nature is full of checks and balances, from multitudes of tiny hard to see creatures to much larger ones such as wolves and tigers. I doubt, however, if Jonathan Swift, author of Gulliver' Travels, had that in mind when he wrote that "Little fish have bigger fish that feed on them and bite ‘em, and big fish have still bigger fish, and so, as infinitum." But it fits perfectly! Swift probably was thinking of fishing, and not about nature’s pyramid of life. And yet we have recently experienced several examples of the relationships between parasitic wasps and other organisms. Think about the enormous flight of snout butterflies, a major explosion in numbers partly because of a significant decline of their parasitic wasps that normally would help keep their numbers in check.

Another recent event provided one more example of a parasitic wasp that is instrumental in controlling another group of insects that has been singing loudly in our neighborhoods. This is the cicada-killer wasp, a fairly large, heavy-bodied wasp with a black abdomen with yellow rings, black thorax, and clear wings tinged with rusty color. It, too, is a deadly predator. Female cicada-killers dig burrows, usually about a foot in depth, and search out cicadas that they paralyze with a sting. Most cicada-killers find their prey above ground in trees. Once it discovers an appropriate prey, it will jab its stinger into the insect's nerve center, paralyzing it. When that occurs, the wasp and prey usually fall to the ground. She will then drag the cicada back up the tree to where she can carry her prey in a direct glide to her burrow. The size of the cicada negates any chance of carrying such a load up and over vegetation. It is much easier, apparently, to drag her prey up the tree and then glide it to its burrow. She will then deposit a single egg on the body of the paralyzed victim. The resultant larvae will then gradually consume its host. And since its burrow usually contains several chambers, it takes several cicadas before its chores are complete.

And anyone who has spent much time in the field, especially in the Southwest, cannot help but notice the large, blue-bodied, reddish-winged wasps known as tarantula hawks. Like cicada-killers, this large wasp seeks out tarantulas to subdue with a sting that paralyzes the spider but keeps it alive. These impressive wasps spend a good deal of their time on the ground walking about in search of spiders. Once an appropriate spider is found, it will sting its prey, depositing just enough venom to paralyze but not kill it. When the spider is subdued, the wasp will then carry or drag its prey, depending upon the size of the spider, to a hole that it already has excavated in the ground. It will then cram the spider into the hole, lay several eggs in the spider's body, and cover the hole with the excavated debris. The wasp eggs will hatch within a few days, and the larvae will consume the body of the living spider.

Such stories occur throughout nature, involving a wide assortment of creatures. A few additional examples involving wasps include the ichneumon wasp that utilizes the eggs of another wasp, wasps and bees, wasps and beetles, wasps and earwigs, wasps and fleas, wasps and flies, wasps and lice, wasps and ticks, wasps and aphids, wasps and huge variety of caterpillars, and on and on.

None of these adult wasps actually feed on their prey. Instead they utilize sap or nectar from flowers. The wasp larvae, however, remain underground, feeding on their victim for several days until they reach full size and their food is depleted. Then, rather than emerging as adults, they spin a silken cocoon in which the larvae remain and develop until the following season. Finally, in summer of the following year, they emerge as adult wasps. And the process begins all over again.

Sunday, August 06, 2006

Garden Spiders Are Becoming More Obvious
by Ro Wauer

Have you ever walked into the webbing of a black-and-yellow garden spider? I did just that a couple weeks ago while visiting Armand Bayou Nature Center near NASA. It was an experience that I will not soon forget! It happened along a trail as I was watching along the ground for butterflies instead of paying much attention to where I was going. Although Betty saw the huge web that was stretched across the trail a second before I hit it, and even tried to warn me, but my forward progress didn't allow me to stop in time. I was suddenly covered, at least the entire upper half of my body, in the spider's yellowish, sticky, webbing.

My first concern, of course, was not necessarily the webbing but the spider itself, where it was going to start eating me alive! First I tried to feel it on my neck or down my shirt, but realized almost immediately that somehow the spider had disappeared, probably fallen to the ground and scampered away. Although that part was heart-warming to realize that I has not in jeopardy of loss of life, my next concern was trying to extradite myself from the amazing mass of spider webbing. Taking my cap off was no easy matter, because it was somehow "glued" to my head, the webbing covered my cap and my head. It took ten to fifteen minutes to tear and/or scrape off all the webbing from my cap, head, and torso. Even afterwards I found an occasional bit of yellow webbing on my shirt or ears.

Actually, this same thing has happened a couple of times right in my own yard, but never to the degree I experienced at Armand Bayou. The webbing belongs to the black-and-yellow garden spider, a species (Argiope aurantia) that occurs throughout most of South Texas. It is one of our largest and showiest spiders, about an inch-long with a black abdomen with yellow or orange markings. The front part of its body is generally gray above and yellow below, and its eight legs, that extend out from the body another inch or so, are long and velvety. For a naturalist who appreciates nature, it truly is a beautiful creature!

Garden spiders are most notable because of the huge web that the female spins between all types of structures, from trees and branches to sheds and bar-b-que pits. Webs usually are three to four feet in diameter, but occasionally they can be up to eight feet across, and they can be surprisingly strong, flexible, and sticky. It is said that spider silk is the strongest natural fiber known, that even steel drawn out to the same diameter is not as strong. The silk threads of garden spiders were once used as cross hairs in telescopes and other fine optical instruments. And what is amazing is that when the webbing is destroyed, like when I walked through it at Armand Bayou, the damaged web will usually be reconstructed during the evening hours.

Garden spider webs have a distinct zigzag band of white, sticky silk running vertically through the center. This white band may also help birds see the net so they do not fly into it. The female garden spider, unlike most other spiders, does not have a nest, but remains either in the center, hanging head-down, or hiding nearby, ready to attack any prey that gets stuck in her net. The webbing is strong enough to capture a wide variety of insects and small lizards and even hummingbirds.

Females are considerably larger than the males and generally command the web; males construct smaller, less noticeable webs in less obvious locations. By fall, the females lay eggs in large pear-shaped cocoons with a brown paper-like surface, hung by threads among the adjacent trees and shrubs. The young hatch during the winter months but remain in the cocoon until spring. The adults usually die during the cooler winter months. So goes the life and times of our colorful garden spider.