Evolutionary dynamics shape two passive defensive mechanisms in Neotropical snake radiations

We mapped the distribution of two defensive behaviors (balling and head hiding) of Neotropical snakes to evaluate its distribution in distinct phylogenetic groups. Balling behavior was observed in 58 out of the 167 examined species across seven families. Head hiding was observed in a total of 100 species across nine families. From the high prevalence of balling behavior in basal groups of snakes, such as Anomalepididae, Boidae, Leptotyphlopidae, Tropidophiidae, and Typhlopidae, and the low prevalence among species of recent diversification radiations, such as Elapidae and Viperidae, we suggest that this behavior evolved in basal groups and persisted in some derived taxa. Balling was not observed in association with other defensive strategies, while head hiding can occur in combination with caudal elevation, caudal vibration, and body flattening. Therefore, head hiding, in contrast to balling behavior, presents itself as putatively more flexible, as it should allow for an escalated degree of defensive displays.