Behaviour of Wrack Diptera -- 1
Abstract
The beach wrack flies Fucellia rufitibia, Coelopa vanduzeei,
and Lentocera johnsoni occupy successive vertical levels
inside banks of mixed wrack found low on California beaches.
When the wrack is washed away, Coelopa are then found at the
toe
sand-wrack flake interface with Lepppmra; Fucellia in a black
band of flies above the highest waterline. Fucellia range
widely up and down the beach. Movement to higher beach positions
at night seems to be associated with temperature, but some

ellia remain in the warmer surface layers of the lower wrack

banks at night. Coelora are usually only found at lower beach
positions where they inhabit the moist interior of wrack banks.
Moisture and tide level are the important factors in Coalona

behaviour. Mark and release experiements show that f.u
do not disperse widely but constitute moreorless fixed communities
on the beach. C. vanduzeei are gregarious. In wrack preference
experiments in the field, Fucellia and Coelopa exhibit strong
preference for the surf grass
lix, probably as a source
Phyllosrad
of shelter. Brown algae and mixed wrack are preferred to the
same degree; red algae very little.
e
-2-
VITT
RUFT
(A.N
BEHAVIOUR OF THE WRACK DIITENANS FUCELLIA
TBT
IIIDAE)

PA VANDUZMET (COELOPIDAE) AND LEPTOCEI. JCHRSCHI
COELOI
(SPHAEROCERIDAE) ON A CALIFORNIA BEACH
Joel D. Hyatt
Hopkins Marine Station of Stanford University
European wrack diptera have been studied mainly as members
of the wrackfauna (Backlund,1945; Egglishaw,1960a,1960b).
Backlund speculated on relationships of Fucellia maritima,
F. frigida, F. fucorum and Coelopa to the wrack, but was more
concerned with dipterous larvae and other residents of the
wrack. Remmert's investigations of the beach flies of Germany
(1960a,1960b,1960c,1965) were broader and included the
structural differences between F
Tucellia intermedia and both
igida and C. pilipes as they might relate to different
Coelonaf
living habits in the beach wrack. He also discussed in more
detail many of the physical factors which influence the wrack
fauna, such as temperature, humidity, salinity, immersion, and
season. No major contributor to the study of wrack fauna has
yet presented a broader picture of the relation and activity of
beach flies to the whole beach, including the wrack itself.
Wrack banks and associated populations of beach flies are
common on California beaches. These flies have been studied
taxonomically (Aldrich,1918) but little is known of their
activity and role in the beach community. The present studies
of the distribution and behaviour of Fucellia rufitibia Stein,
pelopa vanduzeei Cresson, and to a lesser extent Leptocera
asoni Spuler were carried out during April and May, 1972 on
c
Behaviour of Wrack Diptera -- 3
a sandy beach at Hopkins Marine Station in Pacific Grove,
California. These species werechosen out of the many other
species of Ephydridae, Canaceidae, Empididae, Dolichipodidae,
and other Fucellia and Leptocera collected on this beach because
they occur in great abundance, exhibit a specific relationship
to the wrack and yet range over the entire beach. The results
show that each species of fly exhibits specific vertical
zonation within a wrack bank and that there are clear species
differences in range and distribution over the beach.
The study site
Field work was carried out on a protected sandy beach just
west of Hopkins Marine Station at Pacific Grove, California
(Fig. 1). The beach faces the northwest, curves slightly at
the water's edge, and is bordered on each side by rocks. I
established a 25 meter transect from the terrestrial area above
the beach down the sand slope to the water. In the transect
area, the beach was divided into five regions or bands 65 meters
long running parallel to the waterline: 1) the terrestrial

band(
TER) above the sandy portion of the beach, a zone never
covered with water; 2) the high beach(HI), a sandy region
covered with water only during high tides in stormy weather;
(MT
3) the middle beachnD), a band immersed by the highest tides
(above +1.52 m); 4) the low beach (LOW), a zone regularly
covered with water at tides of +0.9 to -1.52 m; and 5) the low
low beach(L LOW), usually exposed only during low tides.
i
K
Behaviour of Wrack Diptera-- 4
Fresh wrack which is deposited low on this beach is nearly
always mixed wrack, composed mostly of the surf grass,
Ihyllosudi but with considerable amounts of red algae (Gigartina
and Iridaea) and brown algae (Macrocystis, Egregia, and I
iminaria).
Green algae contribute very little. Occasionally a large raft
of Macrocvstis washes up as a homogeneous pile of brown wrack.
Backlund's (1945) definitions of wrack forms were used and most
wrack deposited low on the beach constitute wrack banks.
Zonation of flies within the wrack
Individual wrack banks quickly become inhabited by flies.
different species occupying different levels in the wrack. To
determine zonation, samples of wrack at successive levels in
banks were collected rapidly and immediately sealed in plastic
bags. The fly populations were identified and counted in the
laboratory, and the flies then returned to the field.
Newly deposited mixed wrack banks allowed to sit in the
daytime for at least half a day exhibited vertical zonation
by species(Fig. 2). It was found that F. rufitibia occupies the
air above the surface and the top layers of the wrack banks.
Beneath lie C. vanduzeei, followed by L. johnsoni at the sand-
wrack interface. The distribution observed during the day shifts
downward at night such that Fucellia displace Coelopa in the top
rew centimeters. If the wrack bank is disturbed during the day,
both Fucellia and Coelopa distinctively buzz their wings,
nerge from the wrack in a very active state, and fly away.
When disturbed at night and during colder days, the flies,
Behaviour of Wrack Diptera -- 5
espeolally Coelopa, do not fly out but retreat deoper into the
wrack also with audible buzzing. Most flies escape from the
wrack and move onto the open beach when the tide washes over the
wrack banks. Fucellia then settle in a wide band of many flies
om the beach above the highest water line and display a tendency
to move down the beach to the small pieces of wrack deposited
with each retreating wave. Coalopa either settle to form a band
of flies at the water line or hide at the sand-wrack interface
of the next highest wrack flakes or wrack strings along with
johnsoni. In addition to wrack flakes and strings, dry
.
tis holdfasts often dot the beach at MID and HI beach
locations. These are usually uninhabited by diptera, but at
times when the wrack banks low on the beach are washed away,
they become filled with thousands of C. vanduzeei.
The vertical zonation in low mixed wrack banks is not always
displayed. When large sections of Macro
tig are washed up as
wwack, they will usually be covered inside and out with Coelop-
within 2-3 hours, especially during the day. After a few days
fewer Coelopa occur on the surface but most occupy the damp.
mucous interior of the Macro
tis bank. Fucellia are clearly
outnumbered but may be present as individuals.
Factors determining the zonation in mixed wrack banks were
not determined. Certainly newly deposited mixed wrack is very
much the same in physical characters -- composition, wetness.
temperature. Soon, however, the outer layers dry out, enclosing
the wet interior with a dry envelope. In these early stages.
the top layers are much warmer than the inner wrack, thus both
temperature and moisture gradients are present. The surface
e
Behoviour of Wrack Diptera -- 6
layers retain heat during the early night hours, which may
be related to the presence of Fucellia at night in a deeper
distribution than during the day. If the wrack bank is allowed
to sit for a few days, bacterial decomposition raises the
temperature of the wrack interior, providing a beautiful
environment for fly larvae (Remmert,1960b). In general
Fucellia are associated with the dryer, warmer surface layers
and Coalopa with the wet, mucous interior.
Intraspecific relationships or competition might also
contribute to zonation. Often C. vanduzeei are present in such
- +
great numbers, especially with newly deposited Macrocysul
wrack, as to exclude F. ruf
bia. While adequate documentation
is lacking, there is a suggestion that a zonation resembling
that inside wrack banks may occur over the surface of the beach
when lower wrack banks are disrupted. The phenomenon of the
bands of Coelopa at, and Fucellia above, the high water line may
roflect this, although it is complicated by the fact that under
these conditions Coelopa seek out the next higher wrack flakes
or holdfasts.
Distribution, Activity, and Movement
Methods
In order to follow the movement and distribution of flies
on the beach, two 24 hour studies were performed at periods
when relations of day and night to high and low tide were
eseentially opposite. For each study two collection techniques
were used, at two and four hour intervals: 1) sweeps with
Behaviour of Wrack Diptera -- 7
an insect net along each horizontal band (TER, HI, MID, LOW)
across the beach, and 2) a modified Remmert bag (Remmert, 1960a)
for periodic sampling. The latter consisted of a large plastic
bag., layered on the bottom with fresh, mixed wrack and then
N7TI
positioned with the wrack exposed to the air at HI, MID, and
LOW beach locations. The net captures those flies on the wing
or those which can be swept up into a net, while the bags trap
those flies which settle down inside the wrack after a period of
exposure. Flies caught in the net were etherized in the field.
counted, and released in the capture area. At sampling times,
each Remmert bag was quickly closed over its contents and taken
into the laboratory. A new Remmert bag was always left in its
place for the next collection period. On shaking,the flies
moved into the upper portion of the bag which was then constricted
in the middle. Flies were removed, etherized, counted, and
returned to the field. At each collecting period, the
temperatures of the air and top 1 cm of the sand were recorded.
the tide level and the presence of wrack were noted, and general
observations were made.
Results
The results of the two 24-hour studies for F. rufitibia
snow that diel movements up and down the beach.
even under two
different tidal patterns, are basically similar
(Fig. 3). The
differences in amplitude of the movement up the beach on the
two nights may be due to the presence or absence
of wrack low
on the beach. The movement of Fucellia up the beach toward
nightfall coincides with drops in air and sand temperatures,
i
R
u



Behaviour of Wrack Diptera --8
During dusk and early evening, flies are often found dotting
the open surface of MID and HI beach. The typical daytime
behaviour of active flying and movement is replaced by passivity
and walking. The large numbers(N) taken at night reflect the
ease of capturing flies in this susceptible state. Figure 4
shows that Fucellia rufit
aare generally not found in the
warmest sand locations on the beach during the day and not the
coldest sand temperatures at night. In fact it seems as if
ucellia escape extreme heat in the day and cold at night.
preferring a middle range of temperatures,
A different pattern of behaviour was observed for C.
ndureei(Fig. 5). Whereas Fucellia were observed travelling
up and down the beach, Coelopa were nearly always found at LOW
D:TI
and MiD beach and very rarely at higher beach locations. At
1000 many Coelopa were netted. At midnight during tidal ebbing.
more flies were found in the Remmert bags. With the reappearance
of wrack at 0400, few Coelona were caught with either method,
perhaps as more flies reinhabited the natural wrack. This
activity pattern is associated with the day to night transition,
the drop in temperature, changes in humidity and tidal level
with the loss of low wrack banks. In another study(see Wrack
preference, below), a similar activity pattern was found to
occur with the high tides which immersed the LOW wrack banks
Fr
during the day and night (Fig. 6).
fucellia did not exhibit this
Sehaviour.
0

Bohaviour of Wrack Diptera -- 9
Disoussion
On the basis of all the above results and many other
shorter term and more qualitative field observations, a
bi emerges
generalized picture of the movement of P.
(Fig. 7). The activity of Fucellia seems related most
strongly with temperature, which shows diurnal fluotuations
both on the beach and in wrack banks. Fucellia become active
the day and tend to remain between temperature extremes,
during
The relationship to warmer sand temperatures at night compares
to the association with the warmer surface layers of the wrack
at night. Second in importance to temperature is the presence
of the wrack low on the beach, which can spread out the
distribution of flies, even at night, as seen in Fig. 7.
Coelopa vanduzeei range only at LOW and MID beach. Fucellis
have a much greater range of activity up and down the beach.
Observations on the distribution of fly larvae on the beach
correlates well with these observations (Kompfner,1972)
The two studies on Coelopa indicate that it is not darkness
or lower temperatures but rather the rising high tide and the
disappearance of the LOW wrack banks which correlate with the
observed peaks of activity. Physical factors which affect
wrack banks and the vertical zonation of flies in them are very
likely the most important factors influencing the behaviour of
Coelora.
Dispersal of marked flies
Another facet of distribution is the tendency of a
Dehaviour of Wrack Diptera -- 10
population to disperse. Mark and release experiments were
performed to provide some measure of this. Two hundred F.
ufitibig were etherized and marked with a dot of yellow enamel
paint on the back of the thorax. Flies were revived, checked
to be sure they were able to fly, and then released at their
site of capture on the beach. This site was a large mixed
wrack bank which persisted on the beach for six days after
release. Marked flies were visible at a distance of 1-2 meters
and were counted in this manner as well as recaptured in the
insect net. Marked flies seen were located close to the point
of release at the times of observation (Fig. 8). A few flies
were found at greater distances and one Fucellia was spotted
over 100 meters from release, but it is also apparent that many
flies remained in the wrack at night and did not migrate up the
beach(Fig. 80,D). Ira control group, 22 cf 25 marked F.
tibia survived in the laboratory for six days.
rufi
A similar experiment was also performed, using 150 C.
wanduzeei marked with orange enamel paint. Results here were
quite different; none of the flies marked and released was
ever seen again.
The results show Fucellia do not disperse widely and
rapidly, but seem rather to constitute moderately stable
communities on the beach. The failure to observe marked
lopa after release may not indicate wide dispersion but
perhaps the tendency of Coelopa to bury themselves inside
wrack banks, though wrack banks were not searched for marked
flies.. On the other hand Coelopa are gregarious, always found
in large groups in and on the wrack and on the beach surface.
2
Eehaviour of Wrack Diptera -- 11
Large swarms of Coelopa have been observed travelling
laterally across the lower beach. There are also days when
the beach appears to be empty of flies. It would be interesting
to know where the flies are on these days.
Wrack preference
The composition of wrack banks and flakes available on
the beach varies considerably with place and time. An experiment
was performed to see which component of wrack might be preferred
by the wrack flies. Small piles of wrack, 25-30 cm in diameter
and 5-10 cm high, were established on the beach; one pile each
Dhy
of red algae, brown algae, just pullospadix, and mixed wrack.
Six such sets of four piles each were laid out at HI and MID
beach positions over several days in different sequences (red.
brown, mixed, Phyllospadix; brown, Phyllospadix, red, mixed; etc.).
Flies associated with each pile were sampled at selected
intervals by simultaneously dropping an insect net over each of
the four piles in a given set and forcing the flies into the
net by agitating the wrack. The netted flies from each pile
were then etherized in the field, counted, and returned to the
same pile. It was also necessary to examine closely each
wrack pile for flies, usually Coelopa, which had not been forced
into the net.
The results(Fig. 9) show that no one component of wrack
enjoyed an exclusive preference over the others. Mixed and
brown algae proved equally attractive, while red algae always
contained the fewest flies. The surprising result was the great
Behaviour of Wrack Diptera -- 12
preference shown for Phyllospadix, especially at MID beach, by
both Fucellid and Coelopa.
Remmert (1965) bred both Fucellia and Coelopa for a few
generations in homogeneous samples of red, brown, and green
algae and the eel grass Zostera. He reported that red algae
were poisonous for the flies, Zostera did not suffice as food
for them, green algae provided good food but were scarce in
wrack, and that brown algae were preferred above all other plants
by both fly species. My own preference studies provide no
information on the utilization or value of wrack as food. Many
of my field observations, like those of Remmert, show that
flies prefer brown algae above all others. Not only were whole
tis plants found swarming with flies, but larvae were
r
almost exclusively associated with brown algae, even inside
mixed wrack banks (Kompfner,1972). However, while red algae
were least preferred, flies were still present and the effects
of a toxicity, if it exists, were not observed.
My preference tests appeared to sample those transitory
fly populations which at times must occupy the MID and HI beach
locations during disruptive high tides. In these cases a fly
may not be looking for wrack as food or a permanent home or a
site to reproduce but merely as temporary shelter. Here, the
structural characteristics of the wrack may be more important,
and this could explain the strong preference for Phyllospadix.
++
By analogy, the dry, tangled, maze-like holdfasts of Macrod
iis
on the high beach, mentioned earlier, attract Coelona by the
thousands at certain times when the LOW wrack banks have been
destroyed or are threatened by the high tide. This attraction
Bohaviour of Wrack Diptera -- 13
seemingly has little to do with food, as the same holdfasts
are vacant of flies under most other conditions, but more
probably relate to shelter and protection. Similarly, a small
y
pile of tangled, intertwining L lospadix blades offers a
temporary shelter from the wind and dessication. Of the
choices offered, red algae usually dry to very stiff sheets and
do not provide much protection. Brown algae and mixed wrack,
usually dry on the surface, maintain a wet interior which flies
may inhabit.
Mating behaviour
The mounting behaviour of F. rufi
rutibia has been observed
very regularly in flies around piles of bird excrement, which
attract large numbers of flies. They are probably drawn by
the ammonia, amines, sulfides or fatty aoids, which may also
induce courting and reproductive behaviour (Jacobson &
Beroza, 1963). Mounting often ends quickly either because the
female is unreceptive or the male fails to maintain his clasp,
Often as one male hops off a female, others scramble for the
vacant position, especially with the density of Fucallia around
the bird excrement. Occasionally a successful mounting is
achieved and the pair may remain attached for 5-6 minutes.
Fucellia costalis Stein exhibits a different mating behaviour
not associated with the bird excrement and occuring over a wide
area of the beach. When the male nears the female for the firs
time, the female becomes frozen in place for at least one
minute, and the male alternates between standing still and
e
Behaviour of Wrack Diptera -- 1
moving in short hops on a zig-zag circular course around her.
The fomale sometimes turns around and follows his movements,
but she is most often observed motionless or engaging in
cleaning movements. Suddenly the male approaches on the wing
and either the female quickly flies away, or she makes a very
oud and distinctive buzzing with her wings which separates the
pair, or she allows the male to mount. The male if unsuccessful
may follow the female and try again or cease his attempts,
e
Behaviour of Wrack Diptera -- 15
Acknowledgements
Dr. Paul Arnaud of the California Academy of Sciences was
helpful in the identification of these beach flics. George

C. Steyskal, U.S. Department of Agriculture identified Le

or
ni Spuler. I also thank Helen Kompfner for our in the

field discussions on fly adults and larvae, and Dr. Welton Lee
for his help and intorest in my project. I express deep
ratitude to Dr. Donald P. Abbott for his guidance, especially
in the preparation of this manuscript. Other thanks go to
Dr. Isabel Abbott for her wrack soup and to Hopkins Marine
Station.
Behaviour of Wrack Diptera -- 16
References
Aldrich, J.M. (1918). The kelp flies of North America (Genus
Suli
1, Family Anthomyiidae).
oc. Calif. Achd. Soi.,
" 157-179.
Backlund, H.O. (1945). Wrackfauna of Sweden and Finland.
Opus. Ent. Suppl. Lund., 5, 1-236.
Egglishaw, H.J. (1960
a). Studies of the family Coelopidae (diptera).
Lond., 112, 109-140.
Rov. ent.
Egglishaw, H.J. (1960b). The life-history of Fucellia
rit
ima (Haliday). Ent., 93, 225-231.
Jacobson, M. & Beroza M. (1963). Chemical insect attractants.
367-1
Soince, 140, 1
373.
Kompfner, H. (1972). Larvae and pupae of the dipteran genera
Anthomyiidae and Coelopidae on a California beach.
(unpublished manuscript on file in the libra
ry of Hopkins
Stanford University).
Marine Station of
Remmert H. (1960a). Lebensformtypen von strandfliegen (Diptera).
Zool. Anz., 165, 432-438.
Remmert, H. (1960b). Der strandanwurf als lebensraum. Z.
rph. Okol. Ti
2 48, 461-516.
Remmert, H.
1960c). Jahrzeit und makroklima in ih
re
g für die tierwelt des strandanwu:
rfes. Ibid.
bedeutung
18, 504-52
Remmert, H. (1965). Distribution and ecological factors
ackfauna. In:
controlling distribution of European wy
The
Fi
mp. III. (Ed. by
Proc. of the
arin
Biol.
Levring,, pp. 179-184.
Behaviour of Wrack Diptera -- 17
Captions to Figures
Fig. 1. The study site, a protected sandy beach just west of
Hopkins Marine Station. Small wrack banks dot the lower beach.
Fig. 2. Zonation of flies, day and night, in exposed 15 cm high
mixed wrack banks. Range and relative density of flies is
indicated by the length and width of the vertical bands.
tibia in two
Fig. 3. Distribution and movement of F.
24-hr studies made under opposite conditions of tides, April
(Pacific Standard Time,

20-21 and April 27-28, 1972. The number of Ilies is expressed
in the boxes as per cent(ß) of sample (N) at each collection
time at each successive level down the beach transect.
Abundance and location of wrack are shown. A solid black line
connects the population midpoints at each sampling time.
Fig. 4. Distribution of F. rufitibia with the temperature of
the top l om of sand. The movement curves from Fig. 3A,B are
superimposed on a chart of sand temperatures at each position
on the beach at each sample time.
Fig. 5. Distribution and activity of C. vandu
ei in a 24-hr
study from April 27-28, 1972 (time is Pacific Standard Time).
A shows the number and location of flies captured on the beach
at each sample time. E shows the total number of flies caught
by the net and Remmert bag. Tidal cycle and the presence of
wrack are indicated.
e
Behaviour of Wrack Diptera - 18
Fig. 6. Histogram of the total number of C. vanduzeei and
F. rufitibig caught in six preference trials covering 24 hours.
ellia sample
Tide levels and day and night are shown. The F
at 0130 was lost.
Fig. 7. Simplified diagram of the beach as seen from above
P3+
showing population distributions of F. ruilibia under various
combinations of conditions. Day and night are shown but do not
represent a time axis. B and H show conditions with loss of
wrack during the day; E and K with newly deposited wrack; A,F,
G.L, show older wrack beds. F and L show distributions after
loss of wrack at night, while A and G also represent conditions
with newly deposited wrack during the day,
t
Fig. 8. Movements of marked F. rufilibia released at point
Each dot (B-F) represents the location of one marked fly. Scale
is shown by the 25 meter transect line. The dotted line shows
the limits of the preceding high tide, and the wavy line shows
the water level at the time of observation. The fly at the far
right in B was observed at +6 hours.
Fig. 9. Combined results of wrack preference studies at HI
and MID beach positions, representing 128 samples from 6
experiments of up to 6 days duration,
Dehaviour of Wrack Diptera -- 19

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Behaviour of Wrack Diptera -- 20
20


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11
Behaviour of Wrack Diptera -- 21
TIME
OF
0800
160
7
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Behaviour of Wrack Diptera -- 22
TIME OF DAY
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226 320 210 150 130 110 20
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Behaviour of Wrack Diptera -- 23
NET
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13
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0900
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TIME OF DAY


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Behawiour of Wrack Diptera -- 24



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Behaviour of Wrack Diptera
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Behaviour of Wrack Diptera -- 26
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