The blood-squirting mechanism increases survival after contact with canine predators; the trait may provide an evolutionary advantage. Ocular autohemorrhaging has also been documented in other lizards, which suggests blood-squirting could have evolved from a less extreme defense in the ancestral branch of the genus. Recent phylogenic research supports this claim, so the species incapable of squirting blood apparently have lost the adaptation for reasons yet unstudied. To avoid being picked up by the head or neck, a horned lizard ducks or elevates its head and orients its cranial horns straight up, or back. If a predator tries to take it by the body, the lizard drives that side of its body down into the ground so the predator cannot easily get its lower jaw underneath. Population decline A University of Texas publication notes that horned lizard populations continue to disappear throughout their distribution despite protective legislation. Population declines are attributed to a number of factors, including the fragmentation and loss of habitat from real estate development and road construction, the planting of non-native grasses (both suburban and rural), conversion of native land to pastureland and agricultural uses, and pesticides. Additionally predation by domestic dogs and cats place continued pressure upon horned lizards. Fire ants (Solenopsis invicta) introduced from South America via the nursery industry's potted plants, pose a significant threat to all wildlife including horned lizards. Phrynosoma do not eat fire ants. Fire ants kill many species of wildlife and are fierce competitors against native ants which horned lizards require for food (with their specialized nutritional content). Fire ants have given all ants a bad reputation and human attempts to eradicate ants, including invasive species and the native species on which the lizards prey, contribute to the continued displacement of native ant species and decline of horned lizards. The Texas horned lizard (Phrynosoma cornutum) has disappeared from almost half of its geographic range. Their popularity in the early to mid 20th century pet trade, where collectors took thousands from the wild populations to sell to pet distributors, without provision for their highly specialized nutritional needs (primarily formic acid from harvester ants), resulted in certain death for almost all the collected lizards. In 1967 the state of Texas passed protective legislation preventing the collection, exportation, and sale of Phrynosoma, and by the early 1970s most states enacted similar laws to protect and conserve horned lizards in the USA. However, as recently