Questions About Fall Texas Monarch Populations A Texas teacher wonders: Where did the Monarch come from?! "While inspecting milkweeds, I found a larva in its fourth instar (on 9/21/99). I'm wondering how long it took for the caterpillar to reach this stage. If it took a month, that means there were monarchs here in August. Where did they come from? Is there a population here year-round?" Jim Isleib reporting from Broaddas, TX (jisleib@sfasu.edu) Monarch biologist Dr. Bill Calvert responds: "Each year during the very hot days of August and September, both adult and larval monarchs are reported from scattered locations in Texas. One important locus is the Texas Coast, where monarchs breed more or less continuously throughout the summer. They are able to do this because the non-native Mexican milkweed, Asclepias curassavica, presence in irrigated backyards or roadside gardens persists through the hot summer months. "Elsewhere monarchs appear to vacate the state sometime in June and don't reappear until sometime in August. This cycle follows closely the milkweed cycle which die back or disappear during the hot summer months. But widely scattered thundershowers of August apparently can bring up milkweeds sequestered underground thus providing food for monarchs. "The numbers of adults spotted pick up by mid-September apparently brought down by the rare weak fronts that occur during that season. This population of monarchs seems very different from the main mass of migrants that will breeze through in late September and October. They are often found feeding and mating in low riparian (streamside) areas. "Unlike the later migrant masses that always seem to be in pristine condition, they are sometimes very ragged and worn looking. This is especially true of the males. Often the ragged males are mating with not so ragged females. It is likely that these ragged monarchs will not make it to the overwintering areas and will be killed by some Texas frost. "It is tempting to speculate that the ragged males are using their last chance to cast their genes into the future by mating with a "healthier" female that may make it to the overwintering colonies deep in Mexico. But in order for this to work for the males, the females must be reproductive - that is they must have developing eggs in their ovarioles. At this time it is not known whether or not this is true. Research is now being conducted to determine if climatic conditions of Texas' late summer can turn migrant monarchs back on reproductively. We hope to have some results to report to you soon. "In summary, an early population of monarchs appears in Texas in August and September. These early monarchs appear to be different from the later mass migrant population. They are generally in worse condition and they are actively breeding. We do not know how important this late summer breeding population is in the life history scheme of the monarch butterfly. You can help us to find out by observing and reporting the conditions and breeding status of early populations." Copyright 1999 Journey North. All Rights Reserved. Please send all questions, comments, and suggestions to our feedback form