San Gabriel River of Texas: Common Mestras in Central Texas

Our house and seven acres sit on a ridge high above Lake Georgetown, the reservoir that formed when the North San Gabriel River was dammed in 1980. Our property is covered in mature ash juniper and oak, and we kept most it natural. I often walk these woods with our dog Callie, recording the wildflowers and butterflies we encounter. In the late summer of 2024, I saw something unusual: lots of small white butterflies, each with a beautiful splash of orange on the border of the hind wing. I discovered that these were Common Mestras (Mestra amymore), not typical white butterflies, which are in the family Pieridae, but actually a type of brushfoot butterfly from the family Nymphalidae.

Common Mestra’s are tropical butterflies, usually seen only in Mexico and south Texas. For unknown reasons, in some years thousands of the butterflies move northward into central Texas and even as far as north as Oklahoma and Kansas. Records on iNaturalist show that, in most years, observations of Mestras near the San Gabriel River are rare, but there was a dramatic peak of observations in the late summer and fall of 2024, when I saw them. There was also a smaller peak of observations in the fall of 2016.

One of the things you immediately notice about Mestras is that they are weak, fluttery fliers that stay close to the ground and rarely settle, making taking a photograph difficult.

The caterpillar hosts for Common Mestras are the plants in the genus Tragia, commonly called Noseburn. This plant has stinging hairs, which can cause pain if touched, probably the reason for the name Noseburn. When I searched, I discovered a number of small Tragia plants on our property. I can verify that they do sting when you touch them (I don’t recommend sticking your nose on them). Although the plants were there, I didn’t see any caterpillars on the Tragia on our property.

Why so many Common Mestras appeared in central Texas in 2024 is unknown and an interesting question. Was 2024 just a particularly good year for their host plants? Are they responding to changes in climate, moving north when conditions are warmer and more conducive to their tropical nature? As our climate heats up, will Mestras become a common sight along the San Gabriel River? I’m eager to see what happens in coming years.