The Nature Writers of Texas

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Sunday, November 05, 2006

South Texas Butterfly Numbers Peak in Early November
by Ro Wauer

It seems strange that just when our daily temperatures begin to decline that butterflies, both the number of species and total individuals, would increase so dramatically. Instead of finding 30 or 35 species in my yard daily, the number of species can be closer to 50 from late October through much of November. This increase is especially odd for a cold-blooded creature that requires warmth for its mobility and very existence. Most other insects decline in numbers as daily temperatures drop.

The reasons for increased butterfly numbers this time of year are varied. One of the most obvious is the appearance of several species that are either migrants or emigrants that are moving southward. Monarchs are the best known of these, and the only true butterfly migrant. Monarchs move southward from their breeding grounds all across the northern United States and southern Canada, passing through Texas in fall, and continuing to select wintering grounds in central Mexico. In spring, these same individuals will move northward into Texas, lay eggs on milkweed host plants, and most then die. The next generations will continue northward to their summering grounds.

All our other butterfly species that move through our area in fall never return. Some continue southward into Mexico, but others remain in Texas at least until temperatures become unbearable and they die from the lack of nectar or old age. The lifespan of most butterflies is limited to a few weeks only, although monarchs can survive up to eight months and mourning cloaks, an extremely rare species in South Texas, is known to survive for up to eleven months. This large butterfly can hide in protected places in winter, and it may actually fly about on sunny days even with snow on the ground.

Some of our most common emigrants currently present in our area include southern dogface, cloudless and large orange sulphurs, American and painted ladies, and red admiral. The red admiral is an interesting species because it often remains in our area throughout the winter months; in some places it is referred to as a "winter butterfly." Although it can occur in South Texas anytime of the year, it is most numerous from October to April. Although not as widespread throughout North America as the gray hairstreak, it does occur from Guatemala to Alaska.

Another group of butterflies that increase our fall numbers are those that stray northward from their breeding grounds in extreme South Texas, such as the Lower Rio Grande Valley. One of the earliest to appear is the white peacock, a butterfly that also occurs as a temporary colonist in our area. Temporary colonists occur when a female from some distant location is able to find the right kind of larval foodplant to lay her eggs, and those eggs hatch and eventually produce a new crop of butterflies, away from their normal range. Those new colonists may survive for several years, or until an extremely cold prior (like our Christmas 2004 snowstorm) occurs that wipes out the entire population, adults, eggs, and caterpillars. Zebra heliconians (a black and white striped, long-winged butterfly) is one example of a temporary colonist in our area that was reasonable common before the 2004 storm, but has not been seen since. And Julia heliconians also fit into this category. It is long-winged, orange butterfly has become reasonably common this year, although it has not been seen in our area for two or three years. It is possible that with the number of these butterflies this year that it will reproduce and become resident for a few years.

Some of the other more tropical species that are possible this time of year include Florida white; tailed orange; mimosa yellow; soldier, a monarch look-alike; sickle-winged skipper, a species that might better be called “bat-winged” skipper; white-patched skipper; and Laviana white-skipper.

Still a third reason for increased numbers of butterflies this time of year is the general decline of nectaring plants outside of our gardens. And right now some of our best nectaring plants, such as crucitas and bonesets that we grow in our gardens, are in full bloom. These plants act as marvelous butterfly magnets, bringing a wonderful variety of these flying gems to where they are more likely to be found and enjoyed.

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