Most non-beekeeping people consider bees to be a problem,
they have a pointed bit at the rear end which in the minds of the
general public (and some novice beekeepers) they will use at every
possible opportunity.
This is far from true and even if you are stung it is not
much different from pricking your finger on a blackberry thorn or a
rose bush.
The sting itself is a small, efficient, well engineered
device that allows the bee to defend it's own life and it's nest,
against predators.
Structure of the Sting
The abdomen of the honeybee has 10 segments, seven of which
are obvious, the first one... A1 is called the propodeum and is
attached to the thoracic segments and is better described as part of
the thorax, the remaining part is known as the gaster and outwardly
appears to have six segments, the last of these being A7, The
remaining three segments are internal inside A7.
In some other members of the Hymenoptera A8 &A9
becomes an ovipositor, (some of these ovipositors drill into wood in a
similar fashion to that which the honey bee's sting penetrates skin.
The sting mechanism is shown flat above, for ease of
understanding, it is actually much more compact and folded, as the
small lateral diagram shows at right. Comparable structures are
coloured the same in both views. The left side shows the protractor
muscle and is in the protracted position and on the right hand side
the retractor muscle is shown with the right hand lancet retracted.
Note that the forward moving umbrella valve collects venom while the
retracting one collapses.
The Parts of the Sting
The cavity within A7 is called the sting chamber and the
whole of the sting apparatus is enclosed within it when not in use.
The apparatus consists of three pairs of plates, oblong (light yellow),
quadrate (strong yellow)and triangular (dark brown). Two pairs of
protractor and retractor muscles move the quadrate plates up and down
which causes the triangular plate to act as a rocker, converting
linear motion of the quadrate plate into a curved motion in the ramus
(a flexible extension of the lancet). Thus the two lancets are
advanced in an alternating fashion, which gives rise to a vibration
that can be felt by the person being stung. All of this movement takes
place against the oblong plates which form a rigid armature for the
muscles to act against and the triangular plate to pivot about. The
path that the ramus transcribes is also constrained to a semicircular
track by appendages to the oblong plates.
The shaft of the sting consists of three hollow sharply
pointed structures which mesh together rather like the closure of a
'zip-lock' plastic bag to surround a central canal. These are the left
and right lancets (which are barbed) and the central dorsal stylet.
The stylet at its inner end becomes larger and softer, this
structure, known as the bulb, is the reservoir for the venom. It has
a pair of 'umbrella' valves to push venom down into the shaft as it is
forced into the victim. The venom sac and glands that produce other
secretions are connected to the bulb.
The darker component, in the cross sectional drawing at
right, is the stylet and the grey area is the central canal along
which the venom is delivered. Each of the three components is
incredibly stiff, by virtue of the cross sectional shape. (Rolling a
sheet of paper around a pencil, to form a tube, increases it's
stiffness many times.)
The Action of Stinging
When the sting is deployed, the bee bends it's abdomen
downward due to the actions of the muscles that connect the abdominal
plates. The muscle set on the ventral side contracts thereby
increasing the overlap between the sternite plates. On the dorsal side
another set of muscles contract so that the membrane between the
tergite plates is distended. This results in a bent abdomen, which in
combination of the angular ventral movement of the sting shaft (in
turn caused by the furcula muscle). This ensures that the sting shaft
enters roughly perpendicularly into skin of the victim. Perpendicular
penetration is the most efficient as venom is delivered more deeply
and the path through the tough skin is shortest. The force from the
bee's legs, the muscles of the abdomen and the effect of the backward
raked barbs, as the lancets reciprocate alternately, all combine to
produce a thrust that drives the penetration of the sting.
Venom is pumped into the central canal by the reciprocating
action of the lancets, each of which has an umbrella like collector
and valve (within the liquid contained in the bulb) The pulses of
venom are delivered through the canal and squeeze out between the
rubbing faces of the two lancets. This is another feature that is of
high efficiency as the venom comes into contact with a much larger
area of tissue than would be the case if the sting were similar to a
hypodermic needle. The venom also leaks to a small extent from the
exposed portion of the sting shaft providing a pheromone alert at the
earliest possible moment.
This oblique drawing shows the action of the lancets sliding
on the rails of the stylet. The grey outline is that of a needle tip
and is to similar scale. The portion shown is approximately half a
millimetre long and indicates that the sting will penetrate much more
readily than a needle (and we all know how sharp needles are!).
The diagrams have been drawn by reference to many different
drawings and photographs, they are most similar to those found in
H.A. Dade's Book "Anatomy and Dissection".
Originated... 21-27 Aug 2002, Additions... 24 November 2002
