Thread Snakes Slender Blind Snakes or Worm Snakes: Leptotyphlopidae

Slender blind snakes, which are also known as thread snakes or worm snakes, are thin snakes with smooth, shiny scales. Members of this family look much like blind snakes of the family Typhlopidae and the early blind snakes of the family Anomalepididae, since all have tube-shaped bodies that are about the same diameter from head to tail, and all have short heads with mouths that open downward instead of right on the front end of the head. Species within the three blind snake families have small eyes and bodies that are covered with small scales that are the same size on the belly as they are on the sides and back. In most snakes, the belly scales, or ventrals, are noticeably larger. In the three blind snake families, only the scales on the snout are larger.

The slender blind snakes are different from the other two families in several ways. While all are slim, the slender blind snakes are the thinnest. The bodies of most species within this family are no wider than 0.2 inches (0.5 centimeters), and some are as little as 1/25th of an inch (1 millimeter) wide. This gives them the appearance of moving string or thread. The largest species in the family, such as the western slender blind snake (also known as the southwestern thread snake) and the western thread snake, may reach more than 15 inches (38 centimeters) in length, but most of the 93 species in the family are much smaller. The typical adult ranges from 4 to 10 inches (10 to 25 centimeters) in length and no more than 0.05 ounces (1.4 grams) in weight. Another characteristic that sets the slender blind snakes apart from the other blind snakes—and indeed from all other snakes—is their teeth. Slender blind snakes are the only snakes that have teeth on the lower jaw, but none on the upper jaw.

Most slender blind snakes have backs that are all one color. They may be pink, light or dark brown, black, or gray. A few South American species are colorfully striped. The tails vary in length from about 2 percent of the overall body length to 19 percent, but most have tails that take up about 5 to 10 percent of the total length. The tail on a snake begins at the vent, which is a slitlike opening on the underside and toward the rear of the animal. The tail in almost all species of slender blind snakes has a sharp spine on the end. Most have rounded snouts, but some have hooked and/or pointed snouts. In one unusual species, known as the western slender blind snake, the largest of its snout scales glows under ultraviolet light. Inside the body, the skeleton of most slender blind snakes includes pieces of hip and upper leg bones that are leftover reminders of its ancient ancestors, which had working hips and legs. In boas and other snakes that have similar structures, the bony bits sometimes stick out of the body near the vent and look like small claws. These "claws" are called spurs. In slender blind snakes, the leftover bones usually do not poke through the skin. A few species have another odd feature in their skeletons: The top of the skull is missing.