I find their flight northward each spring an exciting part of this great annual cycle. I like to think of it as the end of a remarkable marathon with the exhausted, tattered survivors of the prior year's migration and overwintering reaching their final goal. While the journey south is prompted by the need to avoid freezing temperatures, the remigration north is driven by the deepest need of every mated creature -- to reproduce. Warmer and longer days largely determine the time of the flight out of Mexico each spring. And if there's been sufficient rain, wildflowers will have begun to bloom and milkweeds, to grow, putting on tender foliage for the spring's first brood of larvae. The flight north from Michoacan usually begins in late February to early March with females mating during the last three to four weeks there. Some males accompany them northward and may also mate during the remigration. Interestingly, it appears that the last male to mate with a female fertilizes most of her eggs.

Having mated, the weathered-looking female's sole purpose is to find nectar and one of the 12 to 15 species of milkweed that she will use out of the 106 known species. Females begin to oviposit or lay the eggs of the first brood in Mexico and throughout Texas. And on this voyage males and females tend to travel alone, whereas in the fall they often fly in large groups. Typically, the first Monarchs arrive in the Dallas-Fort Worth area anywhere from the middle of March to the first week of April. It's believed that there are as many as four or five separate broods of Monarchs in North America each year, with each successive generation following the young emerging milkweed, flying farther north or northeast, mating and giving birth. By as early as May, a very few Monarchs have been reported as far north as Oregon, North Dakota, or even Alberta, Canada, though the vast majority doesn't reach northern climes for another month or more.

You can differentiate the adult male Monarch from the female by looking for the male's black scent pouch just off center of each hind wing in the vein nearest to the abdomen. The male stores pheromones in this pouch and releases them to attract females (who, in turn, release pheromones through openings in their abdomen). Also, the black veins in the female's hind wings appear thicker than those of the male. The life cycle from egg to adult is roughly four to five weeks, depending on daily temperatures. Adults (except for the last migrating generation) live for two to six weeks with temperatures above 95 degrees presumably shortening their lifespan. And they appear not to have a procreation-related death - that is, dying once males have mated or females have laid their eggs. Instead, they are thought to die of "old age", depending upon environmental factors.

Monarch larvae are distinctive, having a succession of black, white, and yellow bands around their bodies. Some people mistake Black Swallowtail larvae for Monarchs, but the color pattern is different and the latter have a pair of tentacles at each end of the larva. If you see a similar cat with these tentacles and an additional pair roughly one-third of the caterpillar's length measuring back from the head, then it is a Queen, another milkweed butterfly. The Queen's adult coloration is more of a burnt orange with white spots on the upper wing surface. Unlike the Monarch, the Queen does not make a dramatic migration but usually remains in southern states (in a good year check out blue mistflower in August and September and you will be amazed at the number of Queens). If you see the larva of either butterfly hanging in the form of a "J", then you have come across it just as it is about to pupate. The pupa or chrysalis is a small but beautiful jade green color with a horizontal pattern of gold spots. Monarch and Queen larvae obtain cardiac glycosides or cardenolides from milkweeds, which, undigested, they store in their tissues. As you know, these toxins provide them and the adults with protection against most birds that find them distasteful. However, several bird species in Mexico, black-backed orioles and grosbeaks, have developed strategies that enable them to feed somewhat freely on Monarchs. It seems that Mexican mice have also developed a taste for Monarchs, for they eat great numbers that have fallen from the trees.

There are also populations of Monarchs in southern Florida, the tropics, Hawaii, and Australia. While these don't migrate, those in the northernmost states often begin their journey south by late August. By the end of September the first groups of migrating Monarchs will have reached Texas, even the border of Mexico. Ultimately, many will have flown over 2000 miles from Canada to their roosting sites in the Neovolcanic Mountains of central Mexico (though a tiny minority appear to overwinter along the Texas Gulf coast). Studies have shown that they use thermals to help them glide and soar roughly 50 miles a day (with a one-day record of as much as 250 miles), inexorably moving southwest. Pilots have seen them soaring at over 7,000 feet. Interestingly, the Monarchs east of the Rockies appear to move in two great flight paths or flyways - one through the central plains and one along the East coast - whereas most of those west of the Rockies fly to southern California to overwinter, many in coastal eucalyptus trees. Recent research has indicated, however, that some western Monarchs also overwinter in Mexico, though it's not known if they fly to the Neovolcanics or perhaps to Baja. While experiments using sun compass studies and magnetism (Monarchs have magnetite in their bodies) strongly indicate that Monarchs use both the sun and the earth's magnetic field for orienting, no explanation has been found for roosting during the fall migration. As they travel south, Monarchs roost each night in large numbers, inexplicably selecting the same particular groups of trees along the way that were used by their great (or great-great) grandparents in the fall of the prior year. Although they've never been there before, each fall's migrating generation use these same roosting spots year after year after year.

Most fall Monarchs coming through our area do so in late September or October. On a given day I've counted several dozen nectaring on mistflower in my yard and at least that many enjoying the gayfeather below the Benbrook dam or at the Nature Center. Occasionally you'll see a few around as late as the end of November. I've been guilty of waving my arms and shouting, "It's getting late! Time to fly south!" as if they needed my help.

I've noticed an unusual phenomenon the last two summers. As early as mid-August a Monarch showed up in my garden, spotted the abundance of Mexican milkweed, and promptly laid eggs like there was no tomorrow. This makes no sense, thought I. It's not quite fall, but any Monarch coming through this time of year shouldn't be mating and laying eggs - it should go on to overwinter and mate next spring! So much for generalizations. I finally came across an article by one of our Texas naturalists who recently had observed this same behavior. He theorized that in early August, some third or fourth brood female is born well north of here. Far enough north that (if I may dramatize) she says to herself, "Uh-oh. At this latitude, the first freeze will be upon my offspring before they can emerge from their pupae and fly south. I have an idea. I'll just blast on down to Texas, say, Fort Worth, where winter won't arrive for some time yet and lay my eggs there. Then my offspring will have time to mature and cruise on down to winter in sunny Mexico! Bueno! Here I go!"

Well, whether the theory is valid or not, the upshot is that you may see Monarch larvae on milkweeds in our area in both spring and in the fall. Monarchs in northtern states do not have new broods on their way back south in a manner corresponding to that of the spring generations flying north. The northern brood of Monarchs migrate all the way to Mexico without mating. They are sexually immature (that is, they undergo a reproductive diapause, presumably due to cooler temps or shorter days) and do not mature sexually until the longer, warmer days of the following spring in Mexico.

For those of you who would like to raise Monarchs (or add to their numbers), there are several approaches. You can collect a few larvae along with some leaves of the milkweed that they're on, bring them home and raise them in a glass reptile cage (preferably without reptiles or other predators). An argument for doing this is that you are better ensuring a future for the larvae as adults - taking them out of the realm of numerous predators. Last spring, I hesitated to protect larvae on my own milkweeds and, after parasitic flies and wasps discovered them, the original 36 larvae dwindled to about 12. At that point I decided to raise the remaining dozen indoors. And you may - quite reasonably - argue that Monarchs have gotten by just fine for eons, thank you very much, without such help.

Another approach (perhaps the wisest) is to increase the milkweed population in your own meadow or backyard. Yes, most milkweeds are very difficult to grow from seed, needing light for the seeds and extremely good drainage. Asclepias tuberosa, "butterfly weed", is the plant that you can find in a nursery. It's a good nectar plant and is frequently sold as a host plant. While a Monarch will lay eggs on it in a pinch, A. tuberosa has a relatively low level of toxins, or cardenolides, compared with other milkweeds. A favorite native you can plant is green milkweed, A.viridis, which appears to be highly utilized in our area by Monarchs. Antelope horns, A. asperula, is also extensively used. Another alternative, while not native here, is Mexican milkweed or A. curassavica. It is very easy to grow from seed, is very high in cardenolides, and is thus a favorite host of Monarchs. It's also a super nectar plant. An argument against A. curassavica is that a few scientists run tests on Monarchs to determine the plant source - and thus the insect's likely area of birth -- of the cardenolides in their bodies. So growing Mexican milkweed outside its natural range might give misleading results to their research. If you choose to grow Mexican milkweed and wish to attract the female Monarchs coming through in March, you are better off potting your plant in the fall and overwintering it so that it has sufficient foliage for the larvae in the spring. Whatever your choice, be on the lookout for larvae on the milkweeds at the Nature Center, those along railroad tracks, and those just below the dam at Benbrook and enjoy the great journey. It's just begun.

P. S. As of February 15, the latest reports regarding the overwintering population in Mexico indicate that their numbers appear to be much larger than what was thought during last fall's migration. Freezing rain killed roughly 75% of the estimated 200 million-plus population in the winter of 2001-02. The remigration of 2002 has apparently nearly restored the size of that '01 population, which was one of the largest. In fact, Dr. Lincoln Brower, a leading Monarch biologist, suggests that the '01 population could have been as large as 5-600 million. If that's true, then the losses that winter were truly enormous. Thus, depending on our weather, '03 could be a good year for Monarchs. I hope so, 'cause in another ten days or so, I'll be moving about a dozen 4 gallon pots of Mexican milkweed to the patio, where they will sit awaiting the sunny day when the first tattered monarch comes gliding over the backyard fence.