Life History and Ecology of the Five-lined Skink, Eumeces fasciatus Part 12

Among 217 identified prey items from stomachs and scats of Sonoran skinks (_Eumeces obsoletus_) from northeastern Kansas were remains of three hatchling five-lined skinks. Taylor (1953b:212) recorded that a _Eumeces laticeps_ s.h.i.+pped from Arkansas to Kansas ate an _E. fasciatus_ that was with it in the container. Several authors have recorded predation on _Eumeces fasciatus_ by snakes of various kinds in captivity. Conant (1951:211) recorded that one was eaten by a blacksnake (_Coluber constrictor_) placed in the collecting sack with it. Anderson (1942:211 and 216) recorded that a king snake (_Lampropeltis getulus holbrooki_) and a young copperhead (_Ancistrodon contortrix_) each fed upon them. Hurter (1911:184) recorded that a milk snake, _Lampropeltis triangulum syspila_, placed in a bucket with a _Eumeces fasciatus_ was found swallowing it a short time later and its tail had been broken off.

Ruthven (1911:268) mentioned that stomachs of milk snakes, _L. t.

triangulum_, collected in Michigan contained remains of five-lined skinks. Ditmars (1907:352) wrote that stomachs of several _L. t.

elapsoides_ contained _Eumeces_, and Wright and Bishop (1915:167) wrote of the same kind of king snake in the Okefinokee Swamp region: "It feeds on ground lizards, skinks, swifts, and other snakes and lizards."

Mr. Richard B. Loomis is of the opinion that the five-lined skink is one of the chief food sources for the milk snake (_L. t. syspila_). Having kept many of these snakes in captivity and experimentally offered them different types of prey, he found that individuals inclined to feed would avidly seize and eat skinks and young mice, but other proffered prey, small adult rodents, snakes, or lizards other than _Eumeces_ were either rejected or were taken with some hesitation. These milk snakes have habitat preferences similar to the skink, which would seem to be one of the most available food sources. Loomis recorded in his field notes that a juvenal blotched king snake (_L. calligaster_) 310 mm. in total length, taken on April 8, 1950, seven miles southwest of Tulsa, Oklahoma, had eaten a large adult _E. fasciatus_. Another juvenal blotched king snake that he found under a flat rock near Sunflower, Johnson County, Kansas, regurgitated an adult five-lined skink. Loomis also recorded a juvenal rat snake (_Elaphe guttata emoryi_) and a juvenal pilot black snake (_E. obsoleta_) each feeding on individuals of _Eumeces fasciatus_ in captivity. Uhler, Cottam and Clarke (1939:622) in a study of the contents of the alimentary tracts of 893 snakes of 18 species, from the George Was.h.i.+ngton National Forest, Virginia, found among the prey items only one skink (species undetermined but most probably _E. fasciatus_). It had been eaten by one of the two corn snakes (_Elaphe guttata_) that were examined in the study.

On June 11, 1950, in Skink Woods, a young copperhead 335 mm. in snout-vent length and weighing 27.6 grams, had a gravid female skink in its stomach. Another young copperhead (335 mm., 36.1 grams) trapped near Rat Woods on August 28, 1953, had in its stomach a bob-tailed adult five-lined skink. Many copperheads collected on the Reservation were kept in captivity for short periods, and from them a total of 44 scats were obtained, each scat containing the remains of one or more prey animals eaten in the wild. Of this total, five scats contained remains of _Eumeces fasciatus_, which was one of the more frequent items, although small mammals collectively made up the bulk of the scat contents.

PARASITES

Skinks, like many other lizards, are likely to be infested with parasites. Little attention was devoted to the endoparasites in the present study, but they were noted from time to time. On several occasions small nematodes and flukes were seen in feces voided by lizards which were handled. Small white cysts were seen in the body cavities of several that were dissected.

Harwood (1932:65) examined for endoparasites nine _E. fasciatus_ along with many other reptiles and amphibians collected near Houston, Texas.

Most of them were infested and five kinds of helminths were identified.

Two of the skinks were infested with _Oswaldocruzia pipiens_, a spirurid nematode that was also present in various other lizards, snakes, toads and frogs from the same region; four had _Comocercoides dukae_, an oxyurid nematode also present in various lizards, snakes, turtles, and frogs; one had in its intestine _Oochoristica eumecis_, named as a new species by Harwood, and found only in _Eumeces_; one contained _Cysticercus_ sp. in its body cavity, present in great abundance as white globular structures .6 mm. in diameter (Harwood states that possibly these were larvae of _Oochoristica_). One skink contained _Mesocoelium americanum_, a dicrocoelid trematode which was found also in the brown skink (_Scincella laterale_) and DeKay's snake (_Storeria dekayi_).

The ectoparasites of these skinks consist mainly of chiggers. Wharton (1952:135) lists three species; _Trombicula alfreddugesi_, _T.

splendens_, and _T. gurneyi_. The first species is the common pest chigger of humans and domestic animals in the United States, and south through tropical America. Wharton lists 136 known hosts which are fairly evenly divided among mammals, birds and reptiles; he lists four kinds of frogs and toads. _Trombicula splendens_ is a similar and closely related species which has been recorded from thirty-eight vertebrate hosts including mammals, birds, reptiles, and a tree-toad. _Trombicula gurneyi_ belongs to a separate subgenus and it was originally recorded from _Eumeces fasciatus_ which seems to be one of the princ.i.p.al hosts.

Two of these mites, _T. alfreddugesi_ and _T. gurneyi_, were on skinks collected on the Reservation, and nearby areas. A four year study of the chiggers in this general region by Loomis (MS), Wolfenbarger (1953) and Kardos (MS) has clarified the ecological relations.h.i.+ps of the several kinds of chiggers present, including their local distribution with respect to vegetation, soil type, moisture and temperature, host preferences, and seasonal occurrence. At the quarry, Rat Woods and the pond rock pile, the chigger population consisted chiefly of _T.

alfreddugesi_, while at Skink Woods _T. gurneyi_ was also abundant. In some local situations where they are among the most abundant of vertebrates the skinks probably are important as hosts of _T. gurneyi_.

An individual skink may have dozens of chiggers on it at one time but usually there are fewer.

There are several favorable sites of attachment. The most favored site is in the axilla. There the scales are minute and granular with exposed areas of thin and tender skin, and the chiggers are well protected from dessication and are not likely to be rubbed off as the skink moves about. Other favorite sites of attachment are: about the insertion of the hind limb, about the cloacal opening, on the eyelids and on the toes. Only occasionally are chiggers found attached on the dorsal surface. When attached in protected spots in the tender skin of the axilla or groin, they are often in dense cl.u.s.ters of a dozen or more.

Damage to the skin resulting from the attachment of the first chiggers renders conditions more favorable for the attachment of others. At Rat Ledge and at the quarry, many of the larger Sonoran skinks (_Eumeces obsoletus_) were captured, and individuals were far more heavily infested than were _E. fasciatus_ from the same places. A single Sonoran skink might be found to have hundreds of chiggers, widely distributed over its body with concentrations at the axillae, groins, lateral neck region, and any injured spots where the protective armor of scales was broken. The reasons for the greater susceptibility of _E. obsoletus_ are not entirely clear. It is a larger, less active species with coa.r.s.er scalation, and is more subterranean in its habits.

The chiggers that attach to skinks seem to occasion but little discomfort. There is no local swelling and inflammation such as occurs in humans. The infestations observed in five-lined skinks were not sufficiently severe to cause debilitation or any noticeable symptoms.

There is, however, a possibility that chiggers are vectors of microorganisms causing diseases in reptiles, just as they are for certain mammals (including humans) in some parts of the world.

Bishopp and Trembley (1935:42) record a single kind of tick, _Ixodes ricinus scapularis_ Say, the black-legged tick, as parasitic in its immature stages on _Eumeces fasciatus_. This tick, however, has been recorded princ.i.p.ally from mammals, of which many kinds serve as hosts for its larval, nymphal, and adult stages.

Population

COMPOSITION

Population structure obviously differs from place to place and from time to time. Because of the differences in secretiveness and elusiveness between young and adults and between males and females, true s.e.x ratios and age ratios are obscured. In the period of weeks between the emergence from hibernation and the onset of the breeding season, these skinks tend to be less secretive than at other times, and secondary s.e.xual and age differences in behavior are minimized. A sample at this season should be more representative of the true population composition than samples taken at other times of year. In a sample of 308 skinks available for the month of April, including the collections made on the Reservation and on nearby areas, in 1949, 1950, 1951, and 1952, 36.7 per cent were adult males, 28.3 per cent were adult females, and 35.0 per cent were young. That these figures cannot, however, be accepted as an accurate indication of the population composition is shown by the data from the areas where intensive population studies were made. Data are most complete from Skink Woods. For 292 adults taken there over a four year period, the s.e.x ratio was 100:122.6. On this area after the first year of study a substantial proportion of the individuals recorded were repeaters from one year to the next, and in some cases for three or even four successive years. Many could be definitely a.s.signed to a known age group. By a.n.a.logy the majority of others could be tentatively a.s.signed with some a.s.surance on the basis of measurements, and relatively few were of indeterminate status. By a.s.signing each of these indeterminate individuals to one or another age group, on the basis of greatest probability, the approximate composition of the population could be determined. Of 611 adults, 55 per cent were "two-year olds" (in the season between their second and third hibernations, which was their first breeding season). The percentage was not significantly different in the two s.e.xes.

On the average, a pair of adults produces somewhat more than nine eggs per year. From the time individuals of a brood start their development in the egg until they are breeding adults two years later, they undergo such drastic reduction in numbers that, on the average, approximately only one per brood survives. Most of the mortality probably occurs early, especially before hatching, also in the inexperienced hatchlings, and in the first hibernation. In spring, after emergence from hibernation, young are generally taken in smaller numbers than are adults. Their relative scarcity is only apparent, owing to greater secretiveness, and greater elusiveness when found. In spring, newly matured adults (age cla.s.s about 21 months) may be taken in somewhat larger numbers than young (age cla.s.s about 9 months). The latter obviously must be more numerous, in a stable population however, as the 21 month age cla.s.s necessarily has sustained some loss since it was 9 months old.

Success of the annual brood varies greatly from year to year, depending on the weather and various other factors. In 1949 evidently conditions were near optimum; young hatched early and were especially numerous in late summer. In 1950 these young hatched in 1949 made up 40 per cent of the total catch (excluding hatchlings) in Skink Woods and were relatively more numerous than young of the corresponding age group in other years. In 1951, these young of the 1949 brood, grown to adults, made up 70 per cent of the breeding populations, as against 36 per cent for the corresponding cla.s.s in 1950 and 58 per cent for the corresponding cla.s.s in 1952.

Even after attainment of adulthood, any given age group evidently is subject to annual reduction amounting to at least half its numbers.

Within six or seven years, at the most, the original numbers would be reduced to an insignificant percentage. At an age of four or five years individuals probably have attained their maximum size, with obscured pattern and changed proportions suggestive of advanced age. Occasional individuals possibly attain much greater age, but certainly few live more than five years. Like most small animals, the five-lined skink has a short life expectancy and a rapid population turnover. As compared with mammals of comparable sizes, the small rodents and insectivores that are this lizard's community a.s.sociates and are subject to many of the same hazards, the skink is notably successful, with a much longer life expectancy. For these small mammals the life span is seldom as long as a year. Most kinds of small birds likewise have a life expectancy less than that of the five-lined skink, although somewhat greater than that of small mammals.

DENSITY

The population density changes constantly, following an annual cycle with gradual reduction to its lowest ebb in late June or early July, then rapid increase to a high point a few weeks later when hatching of the single annual brood has been completed. In a normally successful breeding season the population is at least doubled, but reproductive success varies from year to year, as the population responds to weather conditions that are favorable or unfavorable, even where the environment remains fairly stable. In most places, however, local populations continue upward or downward trends for periods of years in response to successional changes which cause progressive improvement or deterioration of local habitats. Local populations are likely to be more or less isolated from others by areas where the habitat does not exist.

Even in an area of favorable habitat such as a wooded hillside of several acres, the population is not at all evenly distributed, but concentrations occur along rock outcrops, and about decaying logs, or stone piles. In intervening areas lacking such abundant shelter, and less productive of food, the population is spa.r.s.e, or there may be no permanent residents.

In view of these traits, and the difficulty of obtaining a representative sample, no precise measurements of population density can be made. During the time required to secure a sample, the population undergoes change. At the pond rock pile, an area of approximately .05 acre, the skinks were found in remarkably high concentrations, 57 in 1949, 85 in 1950, 37 in 1951, and 51 in 1952. These numbers represent population densities of, respectively, 1120 per acre, 1960 per acre, 746 per acre, and 1000 per acre. No such concentrations were found elsewhere, and probably do not occur in natural habitat. The Skink Woods study area of 2-1/4 acres is typical of favorable habitat in the region of the study, and the numbers taken there are more significant. For 1949 the 74 skinks recorded comprise an incomplete sample, and the population density of 33 per acre represented is certainly somewhat too low. For other years the following population densities (exclusive of hatchlings) are indicated: 1950, 92 per acre; 1951, 61 per acre; 1952, 49 per acre.

These figures are only approximate, of course, and it is difficult to judge how accurately they reflect the true numbers. Even the most intensive collecting may be insufficient to obtain every individual on a small area. Within each season there are s.h.i.+fts of range by some individuals, off the study area and corresponding s.h.i.+fts onto it by others, so that the numbers caught in the course of an entire season are somewhat too high. The individuals taken on the study area may regularly range beyond its boundaries to some extent, so that the seeming population density is somewhat too high. Actually this was probably a minor source of error for the Skink Woods study area, as nearly half its perimeter was bordered by an open field uninhabitable for the skinks, and the remaining perimeter adjoined areas much less favorable than the central portion.

Census of the population of the study area by a ratio such as the "Lincoln Index" used in game management studies was scarcely practicable because of the changing seasonal habits distorting the recorded ratios of the s.e.xes and of age groups somewhat differently at different stages of the season. These changing ratios tend to produce an erroneously high population figure, unless separate computations are made from the data for adult males, adult females, and young. Census figures obtained by this method were erratic but seemed to bear out in a general way, the population figures based on total numbers of individuals taken.

In favorable habitat where they occur in high populations of 50 to 100 per acre in spring, these lizards must attain a bioma.s.s of a pound or more per acre. Bioma.s.s in a population probably fluctuates but little during the course of the annual cycle, even though the number of individuals changes greatly. The steady elimination of individuals through various mortality factors, is compensated for by rapid growth of the young.

Summary

Five-lined skinks were studied for four consecutive years in four small areas, totalling approximately ten acres, on the University of Kansas Natural History Reservation, Douglas County, Kansas. The information gained from intensive study on these areas has been supplemented by data from skinks collected elsewhere in northeastern Kansas, and from an extensive literature pertaining to this species.

The genus _Eumeces_, to which the common five-lined skink belongs, has more than 50 species, occurring throughout Central America, North America to the lat.i.tude of southern Canada, and, in the Old World, across southern Asia and North Africa. Within the genus, the five-lined skinks, comprising a dozen species, form a natural group of closely related forms. In this "_fasciatus_ group" nine of the species occur in the Orient, j.a.pan and neighboring islands and the adjacent mainland. The remaining three, including _E. fasciatus_, occur in the eastern United States. Specific differences are to be found in details of pattern, scalation, and size, and, in some instances, they were long unrecognized. _E. fasciatus_ coincides closely in its distribution with the Deciduous Forest Biome of southeastern North America. An early Tertiary deciduous forest in Alaska and probably in the Bering Strait area, evidently growing in a humid, mild-temperate climate, included genera of plants that are now most characteristic of southeastern North America along with other kinds now characteristic of forest remnants in southeastern Asia, and still others characteristic of the western United States. The _fasciatus_ group seemingly dispersed from a northern center that may have coincided with the early Tertiary deciduous forest of Alaska.

_Eumeces laticeps_ almost coincides in distribution with _E. fasciatus_, but does not occur quite so far north, and unlike _fasciatus_ it occurs throughout Florida. Young are similar in appearance but _laticeps_ is a larger, more powerful species, notably arboreal in its habits. _E.

inexpectatus_ much more closely resembles _fasciatus_, and ecological divergence is slight. It is characteristic of hot and dry rocky areas in open woods, and is more southern in distribution, although there is extensive overlap with _fasciatus_ and _inexpectatus_ shares nearly all of its range with _laticeps_.

_Eumeces fasciatus_ is most abundant in well-drained, open, rocky situations within its forest habitat. It is scarce or absent in bottomland forest that is subject to flooding and requires a forest with openings in the leaf canopy so that suns.h.i.+ne patches for basking are available. In northeastern Kansas, at least, woodlands that are browsed by livestock, and have scanty undergrowth, provide better habitat than those that are protected. _E. fasciatus_ is likely to be most abundant in cutover woodland, and may reach greatest numbers in artificial situations, such as old rock piles, or the vicinity of deserted sawmills. In the north, the species is increasingly confined to open situations, while in the south it may inhabit heavily wooded areas. An abundant supply of moisture is a necessity and the species is limited to a climate of high humidity. Dew normally supplies the source of drinking water, without which the skinks rapidly become emaciated and die.

Optimum body temperature was determined to be near 34C., from a series of temperature readings taken both under natural conditions and in confinement under conditions permitting behavioral thermoregulation. By thermoregulatory behavior, active skinks in the wild tend to maintain their body temperatures near this level over a wide range of environmental temperatures. They can tolerate body temperatures only a few degrees higher, but, within a range of several degrees below 34C., efficiency is little impaired and incentive to make readjustment is slight. At progressively lower temperatures skinks become slower and less efficient. They are, however, capable of copulation at temperatures down to 21C, and of feeding at 16C. At 10C. they are slow and clumsy, barely capable of normal locomotion. At temperatures near freezing they are torpid; they can survive temperatures a little below freezing, but cannot survive being frozen solid. More than half the year is spent in hibernation in northeastern Kansas. Weight loss is slight during hibernation.

Normally the skinks emerge from hibernation in early April in northeastern Kansas, several weeks earlier in the southern states and correspondingly later in the northern part of the range. Maximum activity occurs in the period of weeks following emergence; interrupted from time to time by cold weather which necessitates return to torpidity. After approximately three weeks of activity the adults attain breeding condition. Breeding males acquire a salmon red suffusion of the head region. They become pugnacious and fight on sight. Fighting does not involve territorial defense. In confinement males may mutilate or kill each other. In their search for females, and fighting, the breeding males are so much more active and conspicuous than they are at other times of year that published descriptions usually refer to males as red-headed, with no cognizance of the fact that this condition exists for only a few weeks in the annual cycle. Old adult males lose the striped pattern and blue color of the tail of the young, and are golden brown, usually a little darker on the sides. Males find females by a combination of sight and scent. s.e.xual relations are promiscuous, and there is but little courts.h.i.+p behavior. The male pursues the female and grasps in his jaws loose skin at or behind her shoulder region, and maintains this hold during copulation which lasts about five minutes.

Within a few days after insemination, usually in early May, females become actively hostile to males. In late May or early June the gravid females become unusually secretive and excavate nest burrows in damp soil under flat rocks, or in rotten wood of decaying logs and stumps.

The single annual clutch of eggs is laid in June. The average clutch is somewhat more than nine eggs, with larger and older females slightly exceeding younger and smaller females in average productivity. The female remains in the nest burrow with her clutch most of the time, from laying until after hatching. She alters the nest burrow, dampens it in time of drought, keeps the cavity from being filled with loose soil, prevents the eggs from adhering to the sides or floor of the cavity, and she may repulse certain small predators capable of destroying the eggs if they were left undefended. When they are laid, the eggs are approximately 11 7-1/2 mm. and weigh .4 grams or a little less. By hatching time they have enlarged to 15 11 mm. and each weighs about a gram. Recorded incubation periods vary from 27 days to 47 days; development of the embryo is slowed at low temperatures, and eggs experimentally kept in a refrigerator at 11 to 12C. for periods of days hatched later than others of the same clutch that developed under normal conditions, indicating that development was almost halted in the eggs kept at such low temperatures. Eggs are, however, tolerant of a wide range of temperature, and can develop in nearly dry soil, or can survive partial submersion in water for at least two days. Under weather conditions prevailing in 1951, incubation periods of about six weeks were recorded. Incubation may be shortened by retention of ova in the oviducts in early stages of embryonic development. Hatching may occur from the first week of July to mid-August, but in any one year most clutches hatch within two weeks of each other. Hatching of eggs in a clutch extends over a day or two. The hatchling gradually becoming active inside the egg, slits the leathery sh.e.l.l with its egg tooth, and spends several hours in the early stages of emergence. After resting with head and shoulders protruding, becoming adjusted to the outside environment and gaining strength, it lunges from the egg. For a day or two after hatching, the young remains in the nest, being slow and feeble, and handicapped in its movements by the protruding belly distended by the yolk ma.s.s. The female usually remains in the nest cavity for a day or two after the eggs hatch, showing affinity for the young by curling around them protectively. Family ties are broken as soon as the young leave the nest, and they do not return. Hatchlings average a little less than an inch in snout-vent length, and have a sharply defined five-lined pattern on a black ground color, and vivid blue tail. Hatchlings make rapid growth in late summer, and by the time of their retirement into hibernation, the more successful may have doubled in length, and may have increased their original weight, of approximately .3 or .4 grams, more than eight-fold. After emergence from their first hibernation the young continue their rapid growth. When they are a year old, some of them are as large as small adults. However, they can usually be distinguished from adults by the more sharply defined pattern. These grown young retain the hatchling pattern but the contrast between stripes and ground color, and between body and tail is not quite so sharp. Especially in those with regenerated tails, the vivid blue of the hatchling's tail has become much dulled. By the time they retire to their second hibernation, the young have mostly grown to small adult size. A small percentage are r.e.t.a.r.ded in their growth and fail to mature. Upon emergence from their second hibernation, the grown young mature s.e.xually and partic.i.p.ate in the annual breeding season, in early May, and they may comprise the majority of breeding adults. The ratio of new adults to old adults however varies from year to year depending on the varying fortunes of successive annual broods. The new adults overlap older ones in size, but are usually distinguishable on the basis of their coloration, as they retain the striped body pattern (dulled, especially on the head) and with distinctly blue color on the tail. In skinks that are three years old or more, the dorsal stripes have become obscured and partly blended with the ground color, which becomes progressively paler with advancing age. Metamorphosis is most complete in old males, which retain no trace of the stripes or of the blue color on the tail. Old females usually retain the dark lateral area, and the tail is usually bluish gray, with a blue scale remaining here and there if the tail has not been regenerated.

Most individuals lose their original tails, however. By the time the young are approximately two months old, about half have had their tails broken, and by the time they are a year old and have grown to small adult size, three-fourths have regenerated tails. Some individuals may have had their tails broken and regenerated many times. Tails regenerate rapidly and most of the growth is made within the first few weeks. The regenerated tail is not so long as the original lost portion.

Individuals tend to stay within small areas which are their regular home ranges. These ranges are only a fraction of an acre in extent, but vary considerably in size and shape according to the individual and the situation. Home ranges of approximately 90-foot diameter for adult males and young, and a little more than 30-foot diameter for adult females are indicated. A home range generally centers about some environmental feature providing shelter and food, such as a log, hollow tree, or rock outcrop. Activity tends to be concentrated in the central part of the home range. An individual may continue to occupy the same home range throughout its lifetime, or it may gradually alter its range, s.h.i.+fting by slow stages into a new area. Some individuals seem to "get lost" or voluntarily s.h.i.+ft, and settle in a new area which may be hundreds of feet removed from the original range. s.h.i.+fts are most likely to occur after emergence from hibernation, when the lizard finds its habitat somewhat altered. Individuals released in areas strange to them settled down and established new home ranges, either immediately or after brief wandering.

The five-lined skink is a predator, occasionally taking small vertebrates (lizards and possibly newborn mice) but depending for most of its food on invertebrates. Of these it takes a wide variety. Spiders are the mainstay of the diet, and various salticids and lycosids are the kinds most frequently preyed upon. Phalangids are also eaten. Of insects, orthopterans (including roaches, ceuthophilid and gryllid crickets, grouse locusts, and small gra.s.shoppers) are most important in the food. Larvae of moths and both larvae and adults of beetles are also taken in quant.i.ty. Small snails make up an important part of the diet, and the skinks often eat their own sloughed skins. Less frequently taken food items include certain large ants, centipedes, moths, and miscellaneous insects. Rarely the adult skinks may even eat eggs or young of their own species. Prey is found by sight and scent, and consists of almost any small animals within a certain size range (small enough to be swallowed entire, but large enough to make up a substantial part of a meal) of types which are not too heavily armored, lack noxious defensive secretions, and live on or in the ground or decaying wood.

They are ordinarily crushed in the jaws or battered against the ground, and then swallowed entire.

Natural enemies of the five-lined skink certainly include the broad-winged hawk and probably other kinds of hawks and also include various predatory mammals such as the opossum, armadillo, skunks, moles and shrews; snakes (the copperhead, milk snake, king snake, corn snake, and probably others), the Sonoran skink and even the closely related but larger _Eumeces laticeps_. On the Reservation, the short-tailed shrew was certainly the commonest, and probably by far the most important natural enemy. A high proportion of the skinks examined had scars resembling those inflicted by shrews experimentally confined with skinks in captivity. In time of danger escape reactions vary according to the type of enemy and the attending circ.u.mstances. Frequently an alarmed skink may escape into a hole or crevice, running directly to it from a distance of several yards. Under other circ.u.mstances a skink may burrow into ground litter of dry leaves and other debris, or may even dive and hide underwater. One of the commonest escape reactions is climbing tree trunks. It occurs even in gravid females that are slow and clumsy, being weighed down with eggs. Generally the skink stays on the main trunk of the tree, attempting to conceal itself by utilizing the screening vegetation that is available. In the young, especially, the bright blue tail seems to be used as a decoy, for it is carried, arched high and waved conspicuously as the lizard moves about. Rapid las.h.i.+ng movements of the conspicuous tail as the animal darts erratically for shelter may serve to confuse a pursuer, at least as to the direction that the skink has taken.

This skink is parasitized by various helminths, both cestodes and nematodes, which inhabit the digestive tract and body cavity. Some of these infest many kinds of amphibian and reptilian hosts, but others may be confined to the five-lined skink. Their life cycles, and effect upon the host are not well known. Ectoparasites consist princ.i.p.ally of chiggers. Three kinds have been recorded on the skinks; _Trombicula alfreddugesi_, _T. splendens_, and _T. gurneyi_. The first two are common pest chiggers which attack humans as well as a wide variety of other mammalian, avian and reptilian hosts. _T. gurneyi_ is a less common species found mainly on _Eumeces fasciatus_ and confined to its woodland habitat.

LITERATURE CITED