BEHAVIOR AND ECOLOGY OF THE BROAD-HEADED SKINK, Eumeces laticeps

By Bill Cooper

     Broadheaded skinks have long been called scorpions by uninformed rural southerners who believe that they are venomous. Good thing they aren't because they have bitten me hundreds of times with no result worse than a painful pinch and sometimes broken skin. Males during the breeding season have bright orange head coloration, and the heads of large males are proportionally much bigger than those of females. This may be the source of the myth about the venom, but the orange head is not a warning signal to potential predators. Instead, it is a sexually social signal that identifies an adult male in breeding condition. Upon emergence from hibernation, males have tan head coloration. By late April the head turns bright orange under the influence of the male sex steroid hormone testosterone. It stays red throughout the breeding period in May and June, but then fades by July.

     Females breed only once per year, producing a clutch of several eggs, the number of eggs increasing with the size of the female. Thus, males prefer to mate with large females that will produce more offspring. During the mating season males fight over access to females. When two males encounter each other, one may flee immediately or after preliminary behavioral displays. If two males are closely matched in size, they may engage in prolonged and sometimes severely damaging fights. First the males tip their snouts down and display their enlarged orange heads to each other while still some distance apart. They then approach each other, tongue-flicking each others' bodies upon contact to detect chemicals (pheromones) that identify lizards by species, sex, reproductive condition, and even allow identification of familiar individuals. They circle each other warily, sometimes attempting to bite, until one male tilts its head sideways to present the largest possible expanse of head to the rival. The rival then bites the head at its greatest breadth in a test of strength. If the rival is too small or weak to obtain a good grip or deliver a strong bite, it will flee. If the pair are nearly evenly matched, they may bite each other repeatedly, often rolling over and over while biting and sometimes throwing the opponent through the air. Serious injuries sometimes occur and virtually all large males in dense populations show recent head wounds due to fighting.

     The winner of a fight may exclude the loser from his vicinity. When females approach sexual receptivity, they produce a sex pheromone from a gland in the cloaca. This pheromone permits males to locate females by following their scent trails and stimulates courtship. A female nearing readiness to mate may attract of retinue of several males. Females prefer to mate with large males that have demonstrated their fitness by surviving long enough to become large, but frequently the largest male's dominance over other males is the primary determinant of which male mates with a particular female. A large male may guard a female for more than a week to ensure that only he fertilizes her eggs. He follows her throughout the day, usually staying within a few feet of her and often in physical contact. Smaller males that cannot challenge the large male often follow the pair and may attempt to copulate with the female if the guarding male is momentarily distracted.

     After mating, females deposit their eggs in protected spaces such as holes in trees and under the bark of fallen logs in areas that have sawdust that helps retain moisture, reducing the chances that the eggs will die from water loss. Females broad-headed skinks and their close relatives are unusual among lizards in that they remain with the eggs until they hatch. They spend much time in contact with the eggs, often coiled about them. When they return to their nests after brief absences, females may rearrange the eggs and retrieve them if they have been moved. Females may provide protection against small predators and eat damaged eggs that would be hazardous to healthy ones due to fungal growth. Although it has not been studied, movement of eggs and selection of relatively moist substrates suggests that they might also benefit the eggs by assuring that they are exposed to adequate moisture.

     When the eggs hatch in July, their color pattern is totally different from that of the adults. The hatchlings are shiny black with narrow longitudinal yellow to orange stripes that run from the neck to the base of the tail. Contrasting with the rest of the body, the color of the tail is bright blue. In many natural settings the bright blue tail is the first part of the hatchlings that catches the attention of human observers. Although several ideas have been presented regarding possible functions of the blue tail coloration, laboratory experiments have contradicted all except one hypothesis, which is that the blue tail color deflects attacks from the body to the tail. Hatchlings bitten on the body by scarlet king snakes are invariably eaten. However, if the attack is on the tail, the lizard voluntarily severs it from the body, a process called autotomy. Because the bright tail color attracts strike, a high percentage of hatchlings escape. While the snake or other predator is distracted by the tail, which thrashes wildly, the lizard escapes. The tail can be regenerated.

     The bright color pattern of juveniles gradually fades to the uniform tan of old adults. By the end of the second summer the blue tail coloration has disappeared. Although the reasons for the dramatic change in color between hatchlings and adults have not been demonstrated, the shift is probably the result of a change in predator suites with body size. New hatchlings are eaten by a variety of small vertebrates and even small predators such spiders. As they become larger, broadheaded skinks may become energetically attractive prey to larger predators that are more efficient in capturing them. If bright tail coloration increases detectability of the hatchlings by such predators, the increase in probability of escape may not be great enough for the bright tail color to have a net benefit.

     Broadheaded skinks are active foragers that move through the habitat looking for small animal prey although they occasionally eat fruit such as blackberries and grapes. While foraging they flick their tongues out frequently to locate scents of prey. They eat a wide range of small invertebrates, especially insects, many of which are found hidden in or under logs or surface litter on the forest floor. The lizards also tongue-flick to detect the presence of predators and to gather information about other members of their own species. From the scent of another lizard, broadheaded skinks can tell whether the other lizard belongs to the same species, its sex, its reproductive condition, and whether or not it is a familiar individual. Visual cues are also important for feeding, avoidance of predators, and social behavior, but chemical sampled by tongue-flicking are very important in the absence of visual cues or as a supplement to them.

     Broadheaded skinks are semi-arboreal lizards, that is, ones that spend a good deal of time in trees, where they search for food, sleep, seek shelter from predators, and brood eggs, but also spend much time on the ground. They usually occur in deciduous forests, reaching by far their greatest abundance in stands dominated by live oaks, especially large trees having holes. They can tolerate a wide range of moisture conditions from swamps to relatively dry upland with sandy soil. Although broad-headed skinks occur widely in the eastern United States, they typically occur at fairly low densities or are difficult to observe in forests. However, they can be quite abundant in some natural areas, especially on barrier islands on the Atlantic coast, and in disturbed areas with abandoned buildings or pile of logs.

Broadheaded Skink Fact sheet (pdf)