Savory - Arachnida 1977

70 II. DE ARACHNIDIS
using a scanning electron microscope, has seen on the upper surface of
the abdomen knobbed setae peculiar to female Lycosidae. These afford
a firm grasp to the undermost layer of the brood in their precarious
situation. The knobbed setae are not innervated, but long, smooth setae
are in contact with nerves and probably play a part in determining
maternal behaviour.
The characteristic of all these methods is the evident bond between
the spider and her cocoon. Although we cannot know whether the
cocoon appears to her as an object of affection or of value, we are soon
aware of the facts that she resists any attempts to remove it, that if it is
taken away by force her behaviour is conspicuously changed, and that
if it is offered to her again she at once accepts and replaces it, reacting
not to its appearance but to its touch. Investigators have shown that a
deprived spider will accept the cocoon of another spider or any one of a
wide variety of substitutes, such as a pith ball or a pellet of cotton wool
or blotting paper; and in nature such spiders have been found carrying
small shells.
The memory of a bereaved spider for her cocoon varies from a few
hours to a few days, after ·which she will accept neither her own cocoon
nor any substitute. It is believed that her behaviour is dependent on the
state of her ovaries; if the arrival of a new cocoon is near, her memory
is short, although she has carried it for longer than if the arrival of the
new cocoon was in the distant future.
No male arachnid ever shows any parental responsibility and no male
wolf spider has ever been recorded carrying a cocoon.
The time of courtship is but one of the occasions when Arachnida
are in communication with one another, and it is more easily recognized
by ourselves because the movements involved are unusual and conspicuous.
The study of intercommunication in a wider sense is receiving
closer attention, and Rovner ( 1967b) has found that Arachnida can
affect one another by drumming or scraping on the ground, by a display
of colours, and by particular waving of the legs or pal pi. These are
additional to the acts of stridulation, found among scorpions, spiders
and in other orders.
Several of the sounds made by spiders have been recorded, and playback
experiments have proved that spiders can hear air-borne sounds.
8
Ethology: Behaviour
The descriptions of the daily habits of Arachnida given in the last
chapter form an example of >vhat may be called the simple or natural
history method of studying animal behaviour. They attempt to provide
answers to the question: how do these animals behave? They thus
supply material on which to base the more valuable discussions which
attempt to answer the more difficult question: what makes these
animals behave as they do? To do this the different types of activity
must be analysed, classified, and their characteristics defined.
The simplest complete reaction of the nervous system of an animal
is the form of response known as areflex-"aneuro-muscularadjustment
due to the inherited mechanism of the nervous system". The familiar
examples of reflex action, such as the blinking of an eyelid, are often
described with an emphasis on the speed with which the whole system
carries out its function of appropriate response. Thus there is a tendency
to neglect the fact that many important reflexes have to persist for
hours at a time, an uninterrupted series of unit actions. Important
examples of this are the reflexes of posture or of habitual attitude, the
maintenance of which is their chief function. These are called tonic
reflexes. The majority of reflex actions are quickly fatigued and quickly
recover, but the tonic reflexes of posture do not tire in this way. On the
other hand, they are the most easily dispossessed or over-ridden of all,
as if they paid for the continuous use of the nerve-paths by an exaggerated
readiness to make way for other traffic, and in this we can perceive
their nature and function. They form a perpetual substratum of
nervous activity, maintaining the body in a state of dynamic equilibrium.
It is clearly important that this state of equilibrium shall be
upset easily, so that there shall arise that agility of response to the
changing circumstances of life which produces efficiency and successful
activity in the living animal.
A very large proportion of the life of an arachnid is spent in waiting,
and during these long periods of inactivity the tonic reflexes are in sole