A M . ZOOLOCIST, 9:223-227 (1969).
Maturing and Coordination of Web-Building Activity
HANS M. PETERS
Zoophysiologisches Institut, Abteihing fur Physiol. Verhaltensforschung,
Universitdt Tubingen, Germany
SYNOPSIS. Experiments are reported in which 114 Zygiella x-notata Cl. spiderlings were
taken out o[ the cocoon before the time at which they normally left (2 weeks after the
second molt); 67 were placed on wooden frames and 47 on wire frames. Both
groups built partial, irregular thread-patterns at first, and, as they grew older,
constructed more and more regular geometric orb-webs: the transition can be traced
through several stages. The shape of the web, particularly the presence of the
free-sector, was dependent on the frame; webs built in a circular wire frame lacked the
free-sector. It is assumed that the accomplishment of full, regular orb webs is
essentially based on the progressive histological differentiation of the central nervous
system in the spiderlings during the developmental phase under observation; the wire
frame could influence the shape of the web through making construction of a retreat
difficult.
My student, Gertrud Mayer (1953),
came to the conclusion that the behavioral
pattern of the spider constructing its orbweb is completely innate ("rein angeboren"). This view was based on the following observations on Araneus diadematus: Miss Mayer put newly hatched spiderlings into small glass tubes, diameter 2.5
mm. In these tubes the spiderlings could
barely turn and were unable to perform
any complicated movements. Some of them
succeeded in performing the second molt1
within their narrow tube. When they had
reached the age at which young garden
spiders usually start building webs, the
prisoners were released. They were able to
spin a fully normal orb-web, immediately
after leaving their prison. Thus, the
former but less critical experiments of
Eliza Petrusewiczowa (1938) were confirmed.
Years ago I became aware by chance
that spiderlings precociously taken out of
the cocoon, i.e., during a phase in which
they normally do not yet build webs, often
construct very atypical webs. I suggested
that the mechanisms of coordination, unDedicated to the memory of my pupil, Victor
von Harling, who so tragically lost his life shortly
after finishing his essential share in these investigations.
i G. Mayer called it "Kokonhautung". At that
time, we did not realize that this is the second
molt. As Fr. Meier (1967) found with Araneiis
cornulus, the first molt is closely connected with
hatching.
derlying web construction, attain their full
maturity during the time the spiderling
spends in the cocoon. Thus, they would be
able to build a regular orb-web immediately when they normally leave the
cocoon.
Together with Victor von Harling, these
experiments were extended, using Zygiella
x-notata which in Germany starts laying
eggs in autumn.
Figure 1 shows the typical cocoon, artificially opened from above. We took the
spiderlings out of the cocoons and put
them individually on small frames, where
they could spin their webs. We used two
kinds of frames, (1) square frames of
wood, the length of the beams being 70
mm (inside), (2) circular frames, diameter 70 mm, of wire 1-1.5 mm in diameter.
The sort of frame influenced very much the
behavior of the spiderlings.
The results which I will discuss are
based upon 11 cocoons and 114 animals, 67
on wooden frames and 47 on wire frames.
During normal development at 20-24°C,
the young Zygiella hatch and leave the
eggs three weeks after the cocoon was deposited. Four days later the second molt
takes place. After two more weeks the spiderlings begin leaving the cocoon and soon
start constructing a first web. The earliest
web of such a spider was observed one day
after the spider left its cocoon. To test our
hypothesis that the behavioral pattern of
223
224
HANS M. PETERS
web-building becomes mature while the
spider is hidden in the cocoon, we took
samples of spiderlings out of the cocoon
day by day, beginning with the day of the
second molt and ending with the thirteenth
day thereafter, and put them on our
frames. It would have been useless to test
them earlier, i.e., before the second molt,
because they seemed unable to move
around and produce silk threads.
Fic. 2.
FIC. l.
I wish to emphasize that the first web
constructed by a young Zygiella, which has
left its cocoon under natural conditions, is
fully regular, like that of Araneus diadernatus. It shows the characteristic feature
of the Zygiella-web, the so-called "freesector" (Fig. 2). The "signal-thread" runs
through the "free-sector" and connects the
retreat with the hub of the web.
When spiderlings are taken out of the
cocoon and put on wooden frames, nothing happens during the first two days after
the second molt except that they occasionally move around, leaving a "securitythread" or "drag-line" behind. On the
third clay the young spider starts to construct a retreat. A fixed place, first de-
lineated by some threads, is established on
the frame, usually in a corner. These
threads become more and more numerous,
and finally a silken tube to shelter the
spider is constructed (Fig. 3).
This behavior of retreat-building, starting with the third day after the second
molt, could be observed in almost all spiders taken out of the cocoon before they
would have left it by themselves. As is
already shown (Fig. 3) there can be irregular threads leading from the retreat to the
wooden frame. These irregular networks
can contain short tracks of viscid threads
here and there. They correspond to the
viscid spiral of true orb-webs in their
physical properties, i.e., they are very elas-
FIG. 3.
its
WEB-BUILDING ACTIVITY
tic. Microscopic check reveals that they are
provided with droplets of glue.
Besides such networks we also observed
others which were characterized by a more
or less clear centralization. Networks like
these are a transition to others in which we
can distinguish radii, frame-threads, the
viscid spiral, and the auxiliary spiral. But,
as far as the placement of these components is concerned, there can be a high
degree of irregularity.
FIG. 5.
FIG. 4.
Figure 4 shows a web which was built 12
days after the second molt. It is extremely
small and extremely irregular. The viscid
spiral is confined to the jJeriphery. We can
recognize a "free-sector", but this sector is
not truly free, because it is crossed by
several threads.
Figure 5 shows a web woven 7 days after
the second molt, and the "free-sector" is
not very clear. Furthermore, the side parts
of the frame and the distances between the
radii and the viscid threads are extremely
irregular.
An example of a web built 11 days after
the second molt (Fig. 6) is peculiar in that
the viscid threads are confined to the outer parts of the web. ]n the inner parts, the
auxiliary spiral has not been replaced.
Similar webs were observed frequently. We
believe that this phenomenon—lack of viscid threads in the central parts of the
web—is related to another property of
these premature webs, i.e., deficiency of
glue in the viscid threads. This substance
abounded in the outer circles of the spiral,
and it decreased towards the center of the
web. In a few instances there was no glue
on the whole catching spiral.
We noted above that spiderlings which
had been taken out of the cocoon usually
started spinning activity by constructing a
retreat. The general pattern of threads
which can be recognized as an orb-web
appears usually on the fifth day or later.
FIG. 6.
226
HANS M. PETERS
The number of spiders constructing regular webs increases more and more with
each day, and, conversely, the number of
animals confining themselves to the construction of a retreat, and perhaps some
irregular threads in connection with the
retreat, decreases.
By the thirteenth day after the second
molt, almost all of our subjects had constructed their first geometric orb-web.
What did those spiderlings do which had
been placed upon a wire frame instead of
a wooden frame after they had been taken
from the cocoon?
The broad beams of the square wooden
frames, and especially their four corners,
certainly greatly encouraged the construction of a retreat. The thin circular wire
frames, on the other hand, did not offer
such opportunities, and spiders placed on
this sort of frame usually failed to build a
retreat. We believe that this is why spiders
which were given a wire frame usually constructed full orb-webs, i.e., webs without
"free sectors". Spiders which had constructed a web of this kind were perched
in its center.
Figure 7 shows an example of such a
full orb-web, built 15 days after the second
molt. The relatively older age of the spider is the reason for the regularity of this
FIG. 7.
FIG. 8.
web. Needless to say, all that has been said
about the maturation of web-building activity from observations on "sector-webs"
could be demonstrated as well from observations on spiderlings placed upon wire
frames. For example, Figure 8 shows a well
centered but very irregular threadwork
built five days after the second molt.
These are the observed facts from our
studies. I can only offer some suggestions
about their interpretation. One may assume that the maturation of web-building
activity is a rather complex process, taking
place separately in the different parts of
the young organism. When the viscid spiral is confined to the outer zones of a
premature web, the reason for this could
be that the glandulae flagelliformes (Sekiguchi; gl. coronatae Peters) do not yet
produce a sufficient amount of silk. The
lack of glue droplets on the threads could
be interpreted in the same way as a deficiency in the function of the glandulae aggregatae in this phase of development. On
the other hand, the reasons for many other
anomalies of premature webs should be
sought in the field of neural functions.
The early webs seem to demonstrate that
the central nervous system is not yet completely differentiated when the spiderling
is still within its cocoon. At that time the
WEB-BUILDING ACTIVITY
227
neural basis of certain functions would still the phase of development under considerbe lacking or at least be underdeveloped. ation, as has been started with2 another
Furthermore, it seems that the neural sys- viewpoint by Fr. Meier (1967). By comtem as a whole is not yet able to integrate paring the histological stage of the central
the various functions to the degree neces- nervous system with the behavioral state of
sary for performing the complex behavior- the spiderlings, one could perhaps localize
certain functions and, in this way, gain
al pattern characteristic for orb-weavers.
It would be worthwhile to describe these more insight into the neural basis of web
functional deficiencies in a more precise building. One can easily recognize the conand defined fashion. The problem could vergence of this aspect with the laser
be approached from two different direc- studies of Witt (as reported in this symtions. First, by studying more deeply the posium).
behavioral characteristics. Second, and
such a study should be combined with the
REFERENCES
first one, by an investigation of the differentiation of the spider's nervous system in Mayer, G. 1953. Untersuchungen iiber Herstellung
2 In the discussion, P. N. Witt has drawn attention to this paper. Unfortunately, our observations
can be related to the beautiful results of Fr. Meier
only in a very general sense. When we try to apply
the findings of Meier in Araneus cornutus to Zygiella, we have to take into account that at the
time of hatching, the CNS contains only undifferentiated neuroblasts. Histogenesis, i.e., formation of
the various types of neurons and their connections, would take place during the time the
Zygiella spiderlings normally stay within their cocoon.
und Struktur des Radnetzes von Aranea diadema
und Zilla x-notata mit besonderer Beriicksichtigung des Unterschiedes von Jugend- und Altersnetzen. Z. Tierpsychol. 9:337-362.
Meier, Fr. 1967. Beitriige zur Kenntnis der postembryonalen Entwicklung der Spinnen - Araneida,
Labidognatha - Unter besonderer Beriicksichtigung der Histogenese des Zentralnervensystems. Rev. Suisse Zool. 74:1-127.
Petrusewiczowa, E. 1938. Boebachtungen iiber den
Bau des Netzes der Kreuzspinne (Aranea diadema L.). Trav. Soc. Sci. Lettr. Wilno (Trav. Inst.
Biol. Wilno No. 9), 13:1-24.