This post is guest authored by Maureen Wright, a graduate of the Texas A&M Wildlife & Fisheries Sciences Department and Doctorate student in Wildland Resources at Utah State University.
The state reptile of Texas goes by many names, such as
horned frog and horny toad. But how much
do you know about this critter, which are actually a type of lizard? While a few different species of horned
lizard can be found in Texas, the Texas Horned Lizard, Phrynosoma cornutum, has the honor of being the state reptile. Unfortunately, populations of this lizard
have been declining and the species is currently listed as threatened at the
state level. One major threat to horned
lizard populations is the red imported fire ant, or RIFA (Solenopsis invicta).
RIFA are a
non-native species and present a variety of threats to the Texas ecosystems in
which they occur. These ants have both
direct and indirect negative impacts on Texas horned lizards. RIFA will prey upon hatchling horned lizards
and may also eat hibernating adults.
Healthy, non-hibernating adults do not usually fall prey to RIFA. However, the indirect impacts of RIFA can
affect healthy adults, too.
Several
studies have been conducted related to the indirect impacts of RIFA on horned
lizards. One major hypothesis is that
RIFA outcompete harvester ants (Pogonomyrmex
spp.), which are the preferred prey of Texas horned lizards. As the number of harvester ants decreases,
the number of horned lizards decreases. Horned lizards can eat RIFA, but the risk of
being stung usually prevents them from eating RIFA. If an adult horned lizard is stung, the venom
delivered to its system may affect its ability to survive by weakening it; stings
may inhibit weight gain in a young lizard.
If RIFA become a threat near a horned lizard nest, the female may attend
the nest less often, leaving the eggs more vulnerable to attack by other predators.
Texas
horned lizards aren’t completely helpless against RIFA. A study conducted by researchers at the
Caesar Kleberg Wildlife Research Institute showed that Texas horned lizards
have two defensive moves against RIFA, depending upon how many RIFA are
present. If the lizard is confronted by
12 or less ants, it will use the “consumption strategy,” in which it begins to
eat the RIFA until they leave or are all consumed. If there are more than 20 ants, the horned
lizard will display the “flee-and-bury strategy,” in which it sprints to get
away from the ants and then buries itself in the dirt.
RIFA are
not the only threat to Texas horned lizards, though. Habitat alteration, insecticides, and a
decrease in harvester ants due to a decrease in native vegetation are also
contributing factors in the decline of horned lizard populations. Continuing research on the decline of our
state reptile will hopefully lead to better knowledge about how to help their
populations recover.
References:
Allen, C.R., D.M.
Epperson, and A.S. Garmestani. 2004. Red Imported Fire Ant Impacts on Wildlife:
A Decade of Research. American Midland
Naturalist. 152(1): 88-103.
McIntyre, Nancy
E. 2003. Effects of Conservation Reserve Program Seeding Regime on Harvester
Ants (Pogonomyrmex), with
Implications for the Threatened Texas Horned Lizard (Phrynosoma cornutum). The Southwestern Naturalist. 48(2): 274-277.
Todd, Brian D. et
al. 2008. Habitat alteration increases
invasive fire ant abundance to the detriment of amphibians and reptiles. Biological Invasions. 10: 539-546.