The Asp, also known as a Puss Moth Caterpillar, is a dangerous pest that many people are unaware of since caterpillars and moths are typically seen as harmless. The Asp can be found in Texas and other southern states. The UT Houston Medical School offers a webpage with more information about these unusual caterpillars including an explanation of why they are a serious health risk.
Puss moth caterpillars can pose a genuine health hazard. Intense, throbbing pain develops immediately or within five minutes of contact with the caterpillar. Stings on the arm may also result in pain in the axillary (armpit) region. Erythematous (blood-colored) spots may appear at the site of the sting. Other symptoms can include headaches, nausea, vomiting, intense abdominal distress, lymphadenopathy, lymphadenitis, and sometimes shock or respiratory stress. Pain usually subsides within an hour and spots disappear in a day or so -- however, with a larger dose of the venom, it is not uncommon for the symptoms to last up to 5 days.
More information can be found on this website which refers to the asp as the most toxic caterpillar in the U.S. An article on PubMed explains more about the health risk from Asps:
The most frequently reported caterpillar envenomation in Central Texas is by the puss caterpillar or "asp," Megalopyge opercularis. This caterpillar is described by patients and physicians as inflicting intense radiating pain. The intensity of symptoms may be underestimated leading to undertreatment. Adequate treatment protocols have been lacking and those in use are not very successful.