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Biodiversity Blog


It got really cold. What does that mean for Texas biodiversity?

The February winter storm “Uri” saw temperatures drop into the single digits and stay below freezing for days. The last time Austin had single digit temperatures was in 1989, the year the Berlin wall fell, Indiana Jones and the Last Crusade came out, and Taylor Swift was born. So, yeah. It’s been a while.

Uri not only caused havoc for Texans and our infrastructure, but impacted our animal, plant, and insect populations. So how did this extreme cold affect them? Staff from the Biodiversity Collections weigh in.


Pupa web
 Overwintering pupa. (Photo: Alex Wild)

Dr. Alex Wild, Curator in Entomology, states that while deep freezes are rare, Texas does see enough of them so that native insect populations retain adaptations to cold temperatures. Insect activity in Austin is also not a constant through the year, which might seem a surprise to some. Wild states: “When naturalists from northern climates visit Austin in the winter, they are often surprised at the low level of insect activity, even when the weather is a balmy 80 degrees.”

Currently, most Central Texas insects have not emerged from diapause, which is a period of dormancy brought on by extreme temperatures. During diapause, the insect will cease development and also experience metabolic slowing. Also, where insects have been during this storm may have helped them survive. “Many of our insects shelter underground,” says Wild, “where the conditions are more buffered, or they have antifreeze proteins in their hemolymph, their insect blood.” Though anyone’s yard would suggest otherwise, the first native spring flowers will emerge soon. This is when we’ll see the regular season insects also emerge. Then we’ll have a better sese of how they weathered.

“The population changes we’ll most likely see are in non-native species from warmer climates,” Wild says. These species have no evolutionary history with prolonged sub-freezing temperatures. “We’ve been tracking a number of Mexican bees and wasps as they’ve moved northward over the years, and are monitoring them again this season,” says Wild. “Also, introduced insects that feed on our common non-native ornamental plants may also face trouble if their host plants froze.”

Perhaps a silver lining to a rather terrible period in Austin: “We may also get a short reprieve from common pest species like the yellow fever mosquito, Aedes aegypti,” says Wild.


 Cactus post storm. (Photo: Nicole Elmer)

A look outside to the surrounding plant life seems a bit dire right now. Tree branches lay on the ground and brown leaves hang from things once evergreen. Even some of our Texas botanical icons have been hit hard, with agaves drooping and prickly pear cactus split into pieces.

What is killer for plants is water freezing inside of them. When ice crystals form in their cells, it can lead to bursting. You may have seen this on the stalks of some of the more vulnerable species. When water freezes outside of the plant cells, it can cause desiccation.

So how does a plant survive these cold temps? A plant typically protects itself by “antifreeze” proteins and dehydrins that help prevent ice formation. They also accumulate solutes like sucrose and other organic compounds like proline inside their cells.

As brown and sad as things may seem outside, George Yatskievych, Curator in the Billie L. Turner Plant Resources Center, has some words of hope: “Some plants are amazingly resilient in the face of overwhelming cold weather.”

A look past the dead stuff reveals wonders of nature. “As soon as the snow from our recent storm melted enough to expose them,” Yatskievych says, “plants of Taraxacum, the dandelion, started blooming in yards around Austin. However, the yellow flower heads were practically stalkless, positioned right at ground level. Other early spring flowers that bounced back immediately include the chickweed Stellaria, chickweed, and Lamium, or henbit. Still other spring-blooming annuals that were present only as tiny rosettes before the storm seemed to survive well. For some plant species, the thick layer of snow and ice acted as insulation to facilitate their survival.”

Extremes of hot or cold weather are often an important limiting factor on the geographical distribution of plants. “Each species has different tolerances,” says Yatskievych. “Gardeners often learn about this through the USDA’s plant hardiness zones, which are based on the average annual minimum temperature, divided into 10-degree increments.” This goes deeper as even within a species, different populations can vary in how well they tolerate extremes. This is how horticulturists develop plant selections that perform well in different regions.

To return to one of our Texas favorites: “Take a look at the prickly pear cacti around the area,” Yatskievych says. “Some species have had pads mostly die or become broken off or folded over, whereas others have bounced back as though we never had a freeze. In the more tolerant cacti, the plants actually expel water during a freeze, shrink back toward the ground, and become very wrinkly in appearance. They quickly recover their turgidity when conditions improve.”


What about fish in the Lone Star State? “Fish kills have been widely reported, especially along the coast,” says Dean Hendrickson, Curator in the Ichthyology Collection. “Temperature extremes have long been part of the region’s native fishes. And while there may have been some isolated extirpations, we expect that populations of most native species will rebound.”

Hendrickson adds that, like plants and insects, non-native species might not fare so well. Adam Cohen, Collections Manager, sampled in Waller Creek on Friday, February the 19th, the last day Austin would see temps dip below freezing during this storm. Cohen found only dead specimens of the invasive Platy (Xiphophorus variatus), an aquarium fish native to much warmer areas in Mexico. This fish has thrived in Waller Creek since at least 2004, and has long been the creek’s most common and obvious species.

After a weekend of balmy temps in the 70s following the storm, Hendrickson and Cohen expanded the sampling and failed to find any dead or alive Platys. “Our hypothesis was that this long, super-cold spell might have finally removed them from the system,” Hendrickson says. The recent sampling they did certainly seems to support this.

“However,” Hendrickson states, “it wouldn’t surprise us if a small number might have made it through in some artificially-warmed pocket of this complex, highly-urbanized stream with plentiful anthropogenically-warmed inputs. Time will tell.”

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 Washed up kill from the freeze, probably speckled worm eels. (Photos: Carl Wilson)



Turtles Hoffman
 UT Turtle Pond residents, warming up. (Photo: Virginia Hoffman)

As explored in our recent post on what animals do in the cold, reptiles and amphibians experience something called brumation in extreme weather like we just experienced. This is a period of dormancy marked by slowed metabolism and activity, until there is a rise in temperature when the animal will emerge to feed and gather warmth.

“I imagine the majority of our native reptiles and amphibians fared well following the unusually cool temperatures,” says Travis Laduc, Curator of the Herpetology Collection. He explains that during winter, many species of reptiles and amphibians seek out refuges that will provide a thermally-stable temperature, a hiding spot that is insulated from the fluctuations of winter storms. These hiding spots can include underground burrows, crevices, hollowed logs, or even dense piles of leaves and vegetation. 

Did some amphibians and reptiles succumb? “Undoubtedly,” Laduc says, “but overall I think our local populations probably did remarkably well in stark contrast to many local populations of birds and mammals, especially some species of bats.”

Laduc and his students saw some of this in action. When Austin’s temperatures climbed into the 80s on Wednesday the 25th, they found ground skinks at Brackenridge Field Lab, along with several turtles at Lady Bird Lake doing what we all might be wishing to do after a rough few days: bask in the sun.

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