E
Population structure, activity pattern, and food of
Neomachilis halophila (Thysanura: Machilidae)
on a California sandy beach.
Robert Benedetti
Hopkins Marine Station of Stanford University
Introduction
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Neomachilis halophila Silvestri, 1911, originally
described from beaches near San Fransisco, is common
under rocks and in crevices in the high intertidal zone
on California beaches (W.G. Evans 1972, personal communi¬
cation). I have found it most abundant just on the sea¬
ward side of the last terrestrial vegetation in areas
covered with rocks too high on the beach to be disturbed
by most high tides,and especially among rocks piled in
such a manner that a small space occurs between rock and
sand. Little is known of the natural history of this
species. The present study deals with population struc-
ture, diurnal rhythm of activity, and food. All Obser-
vations were carried out near Pacific Grove, California,
at sites on Pt. Pinos and on Mussel Point near the Hopkins
Marine Station, in April and May, 1972.
Population Structure
One hundred thirty five specimens were collected at
Pt. Pinos May 19 and 20. In the laboratory they were an¬
esthetized with ether, sexed, and measured under a dis¬
secting microscope. Females were determined by the pre¬
sence of the elongate ovipositor extending from the eigth
and ninth segments (Lubbock, 1873). Length was measured
from the tip of the head to the posterior end of the abdo-
men, excluding caudal cerci and filament. The results are
shown in Figure 1. Males and females occur in approxi¬
mately equal numbers, but large females are larger than the
largest males. A marked discontinuity in size is seen in
the population. Many juveniles, no longer that 3.5mm, are
present, but the next shortest size class begins at 8.lmm.
In a Californian Lepismid studied by Lasker (1956), sea-
sonal breeding was reported, eggs being found only in April
and May. The discontinuity observed in the present study
suggests a similary limited breeding period, in late winter
or early spring. The numerous juveniles were found right
along with the much larger animals.
Activity Pattern
Preliminary observations indicated that Neomach
2.
O
nalophila remained at rest, mainly on undersides of rocks,
in daytime; at night thoy were more active, and were found
crawling on sand beneath rocks and on the upper surfaces
of rocks. Activity patterns of the population were deter-
mined in two 24-hour periods of regularly repeated field
observation, one carried out at Pt. Pinos and the other
at Mussel Point. At Pt. Pinos, two areas of about 30
square feet each were marked off and examined every 2 or
3 hours for location and number of Neomachilig. At Mussel

Point on site of approximately 30 square feet was similar¬
ly observed. At each observation time animals were cat¬
egorized as either 1) stationary on undersurfaces of rocks,
2) crawling on sand beneath and around rocks, of 3) crawl-
ing on the tops of rocks. The results can be seen in Fig¬
ure 2. The increase in total number seen, decrease in
+.
number on undersullaces of rocks, and increase in number
on sand and on tops of rocks, all indicate that the activ¬
ity of Neomachilis halophila increases with the coming of
darkness, reaches a peak shortly before sunrise, and de¬
clines rapidly at dawn. The early morning peak in activ¬
ity coincides with the period of heaviest dew fall (S.
Johnson, 1972, personal communication).
Food and Feeding
Food studies were carried out on animals collected
m-
at Pt. Pinos May 25 and 26, and Emmediately preserved in
3.
958 alcohol. In the laboratory animals were decapitated
and the whole alimentary canal removed as described by
Lasker (1956). Intestinal contents were removed, mount¬
ed in glycerine, and examined under a compound microscope.
Major categories of food were determined qualitatively.
Six samples of ten animals each were taken over a 16.5
hour period to observe any changes in quantity and nature
of the gut contents.
The results (Figures 3 and 4) show a fair variety of
material occur in the gut of Neomachilis halophila. Uni-
cellular green algae, yeast, and pine pollen are materials
most often found. The unicellular algae are derived from
an encrusting lichen growing on the upper surfaces of the
rocks under which Neomachilis is found. The probable
source of the pollen is the Monterey Pine (Pinus radiata),
the most abundant tree near Pacific Grove shores, and a
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species which produces large quantitles of wind-borne pol¬
len in late winter and early spring. The source of the
yeast is unknown. The other materials found represent
common high beach detritus. In 22% of the animals,
spor
ozoans (Gregarindae) were found in the gut, in numbers
from 2 to 36. The largest numbers of animals with guts
partly or wholly filled were found in early morning, in¬
+
dicating that feeding tends to occur during periods of
greatesthactivity.
4.
E
Summary
Neomachilis halophila inhabits the spaces beneath rocks
of the upper beach and shore areas just below the land
vegetation. Males and females occur in equal numbers, but
large females are larger than large males. Activity is
largely nocturnal, and greatest activity occurs just before
dawn. Common foods include unicellular green algae (from
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lichens), yeast, pine pollen, and vegetable detritus.
Most feeding occurs during the predawn period of greatest
activity.
Acknowledgements
Apprciation is expressed to Dr. W.G. Evans, Dept. of
Entomology, Univ. of Alberta, and to Dr. Pedro Wygodzinsky,
American Museum of Natural History for identification of
Neomachilis halophila, and to Drs. D.P.
and I.A. Abbott
for technical and spiritual guidance during the study.
E
Literature Cited
Lasker, R., 1956. The nutrition of the silverfish Cteno¬
+
lepisma lineata with special reference to cellulose
+
digestion. Unpublished Ph.D. thesis, Stanrord University,
Stanford, California.
Lubbock, J., 1873. Monograph of Collembola and Thysanura.
The Ray Society, London. pp. 201-250.
Silvestri, F., 1911. Contributo alla conoscenza dei Mach-
ilidae. Boll. Lab. Zool. Gen. Agrar. Fac. Agrar.
Portici 5: 324-350.
Figure Captions
Figure 1: Population structure of Neomachilis at Pacific
Grove. California. May 19-20.
Figure 2: Activity pattern of Neomachilis at Pacific
Grove, California.
Figure 3: Gut contents of Neomachilis; showing number of
animals in which various types of food were found.
Figure 4: Pattern of feeding activity of
Neomachilis.
2

SIZE CLASSES (MM)


0
—
—
—

—


2
0.
DAY

00
MAYIS-81972
80
POINT PINOS
60
6 20
Z
:00
12:00
16:00
2400
:0
-50
-20
130
20
2
0:C0
ZMA 26-27
1972
MUSSEL
POINT
KEY
TOTAL NO. SEEN
UNDER RCOK
ON SAND
TOP OF
N ROCR
12:00
16:0
20:
TME
10
L
7
6)

2 5

12.
OL
130
-Y
GUT FULL
21 GUT HALF FULL
CU u
:00
13:00
S:30
10:00 17:00
TIME
UNIOELLULAR
EREEN
X
X
X

ALGAE

VEAST


PCLLER
LV
XX

RVL
SCRASS
OROTOZOAN
481182024
NO OF ANIMALS