Savory - Arachnida 1977

64 II. DE ARACHNIDIS
Scorpions seize nothing but living prey, and are well known to eat
spiders freely and, more surprisingly, consume large numbers of
termites. Frequently the scorpion is attracted towards its victim because
the movements of the latter set up air waves to which the trichobothria
on the scorpion's pedipalpi respond. The popular picture of the vicious
scorpion, formidably armed and scouring the desert, bringing sudden
death in its path, must be modified in the light of observed facts.
Scorpions seldom persist in attacking an adversary that puts up a
spirited defence, and they are unable to injure anything which, like a
large beetle, is protected by hard chitin. They do not often eat each
other- even in captivity they are seldom cannibals if alternative food is
provided. When they have made a capture they rest for a long time
while they consume and their method of lying in wait is well
developed. Berland ( 1948) has described the course of events that follow
when a cockroach is put into a scorpion's cage. The latter does not take
a step, but remains "confident in the ascendancy which its immobility
gives it". The agitated cockroach rushes about and before long it comes
within reach of the scorpion's claws. That is enough.
Solifugae are more active and are also more rapid consumers of
their food, which includes many insects, with termites among them, as
well as bed bugs, which they have been said to relish. \Vhen captive
Solifugae have been offered crickets, they have been known to consume
as many as nine a day. A.s soon as one of the insects came into contact
with one of the long setae on the solifuge's body, there was a short
spring forwards, and a lightning snap of the great jaws. The fact that a
solifuge is eating a cricket will not deter it from seizing another to
follow it; and the crunching of the victim's body can be heard at a
distance of several feet.
This vigorous mastication by Solifugae is very characteristic of the
order. The two scissor-like chelicerae hold the body horizontally, and
as they bite it, they also move backwards and forwards alternately. No
other arachnid eats like this; it is one of the characteristic features of
these animals. Their long leg-like pedipalpi are so important as tactile
organs that the solifuge does not long survive their loss; in this respect
these limbs resemble the equally essential second legs of harvestmen;
and Solifugae also resemble harvestmen in their constant need for water
and their omnivorous habits.
Harvestmen come upon their prey by chance during their nightly
wanderings, and almost alone among Arachnida they are frequent
feeders on dead matter. Their nocturnal habits have not deterred the
enthusiasm of either Bristowe ( 1949) or Sankey ( 1949), who have made
expeditions with the help of an electric torch to discover exactly what
harvestmen do at night. They independently noticed harvestmen eating
7. BIONOMICS: GE?\ERAL HABITS 65
other harvestmen, snails, worms, millipedes, woodlice, earwigs and
flies, all of which the harvestmcn had apparently captured and either
killed or disabled. They were also seen to be eating the bodies of dead
ants and beetles, and Bristowe observed the nibbling of the gills of
fungi. Other observers have told how they have been seen feeding on
dead moles or mice and sucking the juices from bruised and fallen fruit.
An account of the harvestman's method of catching its prey has been
given by Roters ( 1944), who fed his ban estmen chiefly on Hies and
small moths. He wrote that the moths were pursued as soon as they were
put into the cage, the harvestmen reacting at once and beginning to
search, tapping the ground with their second legs. \\'hen an insect was
touched by one of these legs a swift dart forward surrounded the victim
with a screen or palisade of legs, while the pedipalpi sought to make
contact with it. If the pedipalpi touched one of the wings, this wing
was seized in the chelicerae and passed through them until the body
was reached. If the imprisoned moth moved, the harvestman raised its
body aloft and suddenly dropped down upon it like a living pile-driver.
The body of the moth was devoured while the wings were held down
by the harvestman's legs.
Roters' general conclusion was that the choice of prey is less a matter
of taste than of ability to capture it.
If a harvestman is watched while it is feeding, it can be seen that the
food is held in place by the pedipalpi and chelicerae. The forceps of the
latter tear at the skin until it splits, when one pair of forceps is thrust
into the wound, drags out what it can grasp and carries the "handful"
to the mouth. The blades on the coxal segments of the pedipalpi and
the first pair of legs then open and engulf it. The blades of the second
pair oflegs, which in many species are immovable, seem to take no part
in the process, while the function of the lip seems to be to prevent the
loss of fluid from the oral cavity.
A harvestman's feeding is thus different from that of a spider. It is
not limited to fluids which can be pressed or sucked from the prey, nor
is the animal so accustomed to a large meal following, or followed by,
a long fast.
False scorpions resemble spiders and true scorpions in confining
themselves to victims which they have just caught and killed. Cannibalism
is occasional, but is infrequent if other food is available. The
chief diet of the European species seems to be found in the many small
insects, such as spring-tails, which live in the same environment. A
study of the feeding habits of several species has been made by Gilbert
(1951). He recorded the way in which a scorpion will start to
clean its chelicerae with its pedipalpi when the prey is observed, and
says that the victim may be seized either by pedipalpi or chelicerae.