Pesky asps make a home in urban trees netted to deter birds.

While collecting data from live oak trees in the world’s largest medical center, Rice evolutionary ecologists have discovered huge quantities of one of North America’s most venomous caterpillars.

Live oak trees lining sidewalks in the Texas Medical Center (TMC) are routinely netted to discourage pesky birds such as grackles and pigeons. Now Rice researchers have learned the netting has an unintended consequence: Chasing away birds that eat insects has created a haven for a flourishing population of Megalopyge opercularis — asps. The asps bristle with venomous spines that can cause severe pain for humans unlucky enough to come in contact with them. Symptoms include headaches, nausea, vomiting, fever, low blood pressure and, in severe cases, abdominal distress, muscle spasms, convulsions and respiratory stress.

“When we saw such high numbers of asps in the TMC, we knew this was something we needed to look into,” said Scott Egan, an assistant professor of biosciences at Rice. Over a three-year span, Egan’s research team discovered that caterpillar abundance, on average, was more than 7,300% higher on netted versus non-netted trees. Their findings were recently published in the journal Biology Letters. “We thought this was a wonderful, natural, already occurring experiment that we could exploit to understand what happens when trophic interactions get disrupted,” Egan said. 

“It’s very easy to say the birds are a problem and we can fix it by removing their nesting sites, but if you don’t think through the pipeline, you can ultimately create unintended downstream effects,” said Mattheau Comerford, an ecology and evolutionary biology graduate student at Rice. By spotlighting an unforeseen consequence of eco-logical disturbance, Egan and his team hope the study emphasizes the importance of considering ecology in urban planning.

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