Two kinds of ectoparasites were found on ornate box turtles in the
course of the present study; larvae of chigger mites (_Trombicula
alfreddugesi_) were abundant on specimens collected in summer and,
larvae of the bot fly (_Sarcophaga cistudinis_) were found on
specimens throughout the season of activity, and, in a few instances,
on hibernating turtles. In general, these ectoparasites do little or
no harm to ornate box turtles, although heavy infestations may cause
temporary interruption of normal activity or may even cause occasional
death.
Concerning the larvae of _T. alfreddugesi_, Loomis (1956:1260) wrote,
"In northeastern Kansas, larvae become numerous in early June (shortly
after they first appear), increase in numbers to greatest abundance
throughout late June and July, decrease slightly in August, become
markedly reduced in September, and only a few larvae (mostly on hosts)
remain in October and early November." He considered _T. alfreddugesi_
to be the most abundant chigger mite in Kansas and stated (_op.
cit._:1265) that it is most common "... in open fields supporting good
stands of grasses, weeds and shrubs, and where moderate to large
populations of vertebrates are present." Loomis listed ornate box
turtles (_op. cit._:1261-2) as important hosts of _Trombicula
alfreddugesi_ but noted that box turtles are not so heavily infested
as are certain other reptiles. The two other species of chigger mites
that Loomis (_op. cit._:1368) found on _T. ornata_ in Kansas (_T.
lipovskyana_ and _T. montanensis_) were not found in the present
study.
Box turtles were considered to have chigger infestations when the
reddish larvae could be detected with the unaided eye. No chiggers
were seen on turtles in the period from spring emergence until June
13, 1955. On the latter date a few scattered chiggers were noted on
several individuals and it was on this same date that the writer
received his first "chigger bites" of the year. Numbers of chiggers
increased in the latter half of June and heavily infested turtles were
noted throughout July. No chiggers were seen on box turtles after
mid-September in 1955.
Chiggers were ordinarily found only on the soft parts of the turtles'
bodies. Early in the season infestations were chiefly on the head and
neck. Favorite sites of attachment were the point where the skin of
the neck joins the carapace and on the skin around the eyes. Later in
the season some chiggers could be found on nearly every part of the
body where soft skin was present; concealed areas of skin, such as the
axillary and inguinal pockets, the anal region, and the inner rim of
the carapace (where it joins the skin of the body), harbored
concentrations of chiggers. Juveniles were relatively more heavily
infested than adults and, even early in the season, had chiggers
attached along many of the interlaminal seams of the shell. Broad
areas of soft, newly-formed epidermis on the shells of juveniles
probably afforded a better place of attachment to chiggers than did
the interlaminal seams of adults. The interlaminal seams and
transverse hinges of adults were not infested until the height of the
season of chigger activity. Heavily infested adults, observed in early
July, were literally covered with chiggers; red larvae outlined nearly
all the scutes of the shell, the anus, the mouth, and the eyes. When
turtles were picked up for examination, chiggers could be seen moving
rapidly from one interlaminal seam to another.
Box turtles kept in outdoor pens and in the laboratory did not long
maintain visible infestations of chiggers, even during the time in
summer when turtles found in the field were heavily infested.
A four-year-old juvenile was found nearly immersed in the shallow
water of a pond on July 4, 1955; its right eye had been damaged by an
especially heavy concentration of chiggers. When I released the
turtle, some 50 feet from the pond, it returned to the water and spent
the next four days there. The turtle was probably in a period of
quiescence induced by the eye injury and the heavy infestation of
chiggers; immersion in water could be expected to help free the turtle
of chiggers and to relieve trauma resulting from the injured eye.
Richard B. Loomis told me that larval chiggers are able to survive
under water for several days but that warm water will hasten their
demise.
Infestations of larval bot flies (_Sarcophaga cistudinis_) were noted
in several turtles at the Damm Farm and, upon closer scrutiny, were
found to be common in preserved specimens from other areas. Larvae
were always found in flask-shaped pockets (Pl. 27, Fig. 2) beneath the
skin; the pockets opened to the outside by a small hole, the edges of
which were dried and discolored. One larva sometimes protruded from
the opening. The inside of the pocket is lined with smooth, skinlike
tissue. Heavily infested box turtles may have four or five such
pockets, each containing one to many larvae. The most frequent sites
of the pockets are the skin of the axillary and inguinal regions, and
the skin of the limbs and neck, especially near the bases of these
members. Subadults were more heavily infested than older adults; no
infestations of hatchlings or small juveniles were noted.
An adult female, infested with bot fly larvae when she was removed
from her hibernaculum in late October, 1955, bore no trace of larvae
or of the pocket that had contained them when she was recaptured the
following June. According to Rokosky (1948), the larvae eventually
fall to earth and pupate. The individuals of _T. carolina_ studied by
him were not re-infested by adult bot flies; one turtle ate some of
the larvae that dropped from its body.
The manner in which box turtles are infested by bot fly larvae is
uncertain. Possibly the eggs are picked up accidentally or laid on the
skin while box turtles are foraging in dung. Belding (1952:841)
classifies the genus _Scarophaga_ as semi-host-specific, depositing
eggs in open wounds.
McMullen (1940), Rodeck (1949), and Rainey (1953), described
individuals of _T. ornata_ parasitized by _S. cistudinis_. Rokosky
(1948) and Peters (1948:473) reported infestations in _T. carolina_.
Infestations were the cause of death in the instances noted by Rainey
and Rokosky.