The Scolecophidia, commonly known as blind snakes or thread snakes, are an infraorder of snakes. They range in length from. All are fossorial. Five families and 39 genera are recognized. The Scolecophidia infraorder is almost likely paraphyletic.
Systematics
Etymology
The infraorder name Scolecophidia derives from the two Ancient Greekwords or σκώληκος, meaning "earthworm", and , meaning "snake". It refers to their shape and fossorial lifestyle.
Families
Biogeographic history
Scolecophidians are believed to have originated on Gondwana, with anomalepidids and leptotyphlopids evolving in west Gondwana and typhlopids, gerrhopilids, and xenotyphlopids on east Gondwana, initially on the combined India/Madagascar land mass, during the Mesozoic. Typhlopids then dispersed to Africa and Eurasia. South American typhlopids appear to have evolved from African typhlopids that rafted across the Atlantic about 60 million years ago; they, in turn, dispersed to the Caribbean about 33 million years ago. Similarly, typhlopids appear to have reached Australia from Southeast Asia or Indonesia about 28 million years ago.
The common name of Scolecophidia, blind snakes, is based on their shared characteristic of reduced eyes that are located under their head scales. These head scales are found in all snakes and are referred to as spectacles, but within this infraorder, they are opaque, resulting in decreased visual capabilities. Reduced eyes of the Scolecophidia have been attributed to evolutionary origins of snakes, which are hypothesized to have arisen from fossorial ancestors, causing a loss of genes related to eyesight that later evolved again in higher snakes to be similar to other vertebrates due to convergent evolution. Other shared characteristics include an absent left oviduct in four of the five families, aside from the Anomalepididae, which have a well developed yet reduced left oviduct. Aside from this, these snakes range in length from 10 to 100 cm. Their typical body shapes include slender, cylindrical bodies and small, narrow heads. All these families either lack or have a vestigial left lung and lack cranial infrared receptors.
Behavior
The main shared characteristic found across all Scolecophidia is a fossorial nature, either living underground or within logs and leaf litter. Aside from this, thus far the reproduction remains understudied with all Scolecophidia studied thus far being noted to be oviparous, with elongate eggs noted in both leptotyphlopids and typhlopids. Foraging behaviors vary across families, but all feed on invertebrates. Some of their main food sources include ant or termite eggs, which are tracked down by following chemical cues left by these invertebrates to create trails. Tricheilostomata macrolepis has been seen climbing up trees and waving its head side to side vertically to detect chemical cues in the air to locate insect nests. In a study on the Leptotyphlopidae, some species were found to specialize in eating only termites or ants; some rely on binge feeding patterns, while others do not. While these snakes are often difficult to locate due to their burrowing habits, they are more often seen above ground after rain due to flooding that occurs in burrows. The ancestral nature of the Scolecophidia has resulted in the use of these organisms as models for evolutionary studies in Serpentes to better understand evolution of reproduction, morphology, and feeding habits.
