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Psyche 11:47-53, 1904.

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Zoology. W. L. W.
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1
EARWIGS (ANISOLASIA AfA R/T.SfA BON.).
. -
BY CHARLES BARROWS BENNETT, PROVIDENCE, R. 1. IN the summer of 1 got I found a place near Cold Spring Harbor, N. Y ., where there were many earwigs.
As these insects are rather rare in New England. I watched themas :nu& as possible, and also captured several, from which others were reared-
-
THE EGGS AND YOUNG.
Eggs were laid mainly in the warmer months of July and August, and only a very few after the middle of September.
When first laid the eggs were almost two millimeters (about one-sixteenth of an inch) in length, were cylindrical in form, and white, and covered with an almost transparent, glossy shell. (See Figure I, e.) At first the color of each egg was uniform throughout, and its shape was regular. After some days the contents became separated into a clearly outlined embryo and acolorltss liquid. The embryo was of a crescent shape and the side of the egg on which it was became a little larger and less regular than at first. After about
seventeen days- although the time varied with varying conditions of temperature, humidity, etc.- the young emerged from the egg. Their length at that time was seven and a half millimeters (about five-sixteenths of an inch), not including the length of the antennae. (See Figure I, d.) They had, even then, forceps, or
nippers, shaped like those of the adult female, although, of course, much smaller in size. At this stage the antennae were longer in proportion to the length of the body than they were in the adult. In a few other points also the young differed slightly from the adult, but for the most part they resembled them in miniature. Their color when newly hatched was almost white, but soon becam above and brownish below, the same as that of their parents. GROWTH AND DEVELOPMENT.
I was not able to ascertain positively how many times the young ear their skins; it was probably four times. The fact that the genera! characteristics remained the same until the last change, together with the fact that they speedily devoured their own cast-off skins, made it difficult to be sure, at times, whether or



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48
PSYCHE [June
not achange had been made. The last change, I think, was usually made in the spring following the year in which the eggs were hatched; that is to say, they usually winter in the nymph stage. In confinement, however, I have had them winter also in the adult stage.
All the young up to the last nymph stage have ten plates, or tergites, on the dorsal surface between the last pair of legs and the terminal forceps. In the last
part of the nymph stage, however, some of the females have only nine phtes fully showing, with just the tip of a tenth. I found that this was due to the fact that the plate next to the last -that is, the ninth- gradually slid under the one ante- rior to it - or the eighth - until it was nearly lost to sight. No male earwig that I have ever seen had this peculiarity.




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made in the
to say, they
e bad them
gites, on the
is. In the last
line plates fully
to the fact that
sr the one ante-
lale earwig that
The females, after they have shed their skins for the last .time, have only eight plates on the upper side of the abdomen. The easiest way, therefore, to distinguish the adult female from the young is to count the number of its plates; for the genera1 shape both of the body and of the forceps is essentially the same in both. The case of. the males is different. Although until the last change of skin their forceps were not distinguishable from those of the adult femh or the young of either sex, after that the forceps were much more curved. (See Figure I, a, b, and c; a and c are adult males, and b is an aduir female.) Their plates also, after this I
last moult, seemed to overlap each other dong the sides of the abdomen to a greater extent than did those of either the females or the young. The posterior
end oå the abdomen seemed broader in proportion to the size in the male adults than in the other sex or in the younger earwigs. The abdominal plates also remained ten in number, as in the nymph stage. The legs of both male and female adults were of a uniform tan color, while those of the young were generally more or less dotted with black.
Female adults are, as a rule, longer and otherwise larger than the males. The size of the full-grown insects which I have seen varied from almost sixteen millimeters (fiveeighths of an inch) to nearly thirty-five- milli- meters (about one and three-eighths inches), not in either case including the length of the antennae.
I have not been able to ascertain the length of life of earwigs when wild, but one which 3 still have in confinement has lived about twenty-one months. The females were three or four times as numerous as the males. HARDINESS.
Earwigs seem to be capable of great endurance. They live near water, and when disturbed they frequently enter the water. One of them
remained under water for an hour and five minutes or more when disturbed above water.
It showed little sign of being weakened by its experience. They are
capable of recovery from quite serious injuries. Once when an earwig was by accident nearly torn in two just below the last pair of legs, and was consequently paralyzed for a while in one leg and most of its abdomen, I pushed in all the viscera as far as possible with a wooden toothpick, and then closed the opening. In a short time it seemed to be as well and as able-bodied as ever. They easily to lack of water ;
if kept in




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PSYCHE
It is certain that these earwigs are at least partly carnivorous. Any dead
insect not protected by too tough a covering will serve them as food. In captivity
they also eat cooked fish, chicken, and mutton, and both raw and cooked beef. They probably would also eat raw fish, fowl, or flesh of any kind if given them. The fact of their eating their own cast-off skins has been already noted. Whether or not they eat any vegetable food is a question, despite the common belief that they do. Certainty I have never seen one that did. I caught and dissected three earwigs and found that the alimentary tract of two contained animal matter only - very small insects, etc. In the stomach of the third, it is true, there were a few particles of starch, but this may have been accidentally eaten together with animai matter. Those which I have freshly caught, and those which I have kept in con- finement for some time, would readily eat animal matter, but refused vegetable j * i
matter.
F j1 SOME HABITS NOTICED.
Ì -
,!
#
I found that the earwigs were not at all afraid of entering the brackish water -5
'in the bay at Cold Spring Harbor, where they were found. Some voluntarily swam M about from place to place.
Perhaps they more properly floated than swam, for \ å
Ì
their movements were mainly on the surface of the water, and often their backs '3
:J
i
were perfectly dry. When frightened, however, they would often crawl to the under side of some Seating object and hide themselves under water. Earwigs easily dig holes in the sand. Those which I have observed used only their mouth-parts in digging.
They never kicked or pushed the earth out with P their feet.
2
. .
Earwigs, do not seem to be nearly as much afraid of the light as are our j i
common centipedes (Lithobms awerWajirts'), They are said to be nocturnal in their :'
i
habits, and to hide themselves by day " in any dark cranny that they can find," !<;
but those which I studied often apparently preferred the 'light to the darkness, although as a rule they chose the darkness. I have observed that whenever the ground was wet an earwig walking over it would so twist its heavy abdomen that the narrow side rather than the flat bottom would come in contact with the ground and thus serve as a runner to support its weight.
EGG LAYING AND CARE OF THE YOUNG.
When about to lay her eggs the female would make a little chamber for herself in the ground about half an inch deep, and one, or one and one-quarter, inches



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s, Any dead
In captivity
cooked beef.
if given them.
:ed. n'hether
ion belief that
lissected three
matter only-
ere were a few
let with animal
ve kept in con-
used vegetable
brackish water
oluntarily swam
than swam, for
ften their backs
awl to the under
served used only
earth out with
light as are our
loctumal in their
t they can find,"
to the darkness,
g walking over it
n the flat bottom
ler to support its
amber for herself
ae-quarter, inches
wide. This was hollowed out beneath a log or some other object that rested on the ground.
In making this chamber she carried the earth out in her mouth-parts, as already suggested, a little ata time, JUS~ as an ant would do, She never seemed
to use her forceps for either digging or carrying the earth. The chamber is made perfectly clean ; no sticks or bits oE wood or pebbles arc- allowed by the more careful females to remain inside. Here she deposits her eggs. In the chamber of
one wild earwig I counted about ninety eggs, but none of those I have had in captivity laid quite so many at one time, some laying only twentyfive or less. Immediately after the eggs were laid the female picked them up in her mouth-parts, one at a time. and wiped them all over. It looked, indeed, as if she rolled them in her mouth. However that may be, when rhe process is over the eggs are all clean and glossy. Then she places them in a neat pileand stands guard over them. Whether or not it be true with the wild insect, some of the females I have kept for observa- tion have, before their eggs were hatched, moved them all several times from pla& to place, carrying them one at a time. Some of my earwigs refused to touch food of any hind, so far as I could see, from the time they laid their eggs until the young were hatched, while others would leave their eggs at times to get something to eat Several times the females, after caring for their, eggs a while, have eaten them. I have reason to think, however, that in nearly every case the eggs had already spoiled or dried up before this occurred. The females continued to guard their young for a few days after they were hatched. When, however, they had
once left her to seek for food for themselves, they could not safely return lest she should endeavor to eat them.
One earwig which I kept in confinement deposited four fairly large. batches of eggs in one summer.
The opinion has been advanced that the main use of the forceps is to furnish the earwig with an instrument with which it may fold away its delicate wings. That this is certainly not the only use I was assured by observing those which I kept in captivity. In the first place these were wingless,- the AviisoJabia maritima, BOIL, -yet had thoroughly developed forceps. In the second place I detected at least three uses to which the forceps were put without regard to wings. These were (a) for defense, (b) ‰â oftense, and (c) as feelers in mating. (a) That the earwigs used their forceps defensively was apparent. When one was picked up, it always tried to pinch its captor; when touched or molested by another insect in any way, it always used its forceps ; in fact these forceps were the chief, and seemed to be almost the only, weapon of self-defense which they



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s2 PSYCHE
[Jme
i.
had.
(b) The use of the forceps offensively may have been less important, but was scarcely less evident.
I have often seen large earwigs in confinement chase !
and catch with their forceps crickets, sand-Seas, and even smaller earwigs, which they then proceeded to eat. When a victim was once caught, generally no i
amount of struggling freed it again from the powerful grasp of the forceps. When
\
the victim continued to struggle for some time, the earwig which had caught it would, AS 1 have often noticed, curve its own body side\vise until it took the shape of the letter W and its mouth could be brought into contact with its prey. Then the earwig would proceed to eat the living food it was holding. I have also seen earwigs clutch their victims in their forceps and drag them about from place to !
-
5 . I
1
9
. I.
' ,
4
it i
t
and caught their prey, while I was
thelopen.
The earwigs which I watched would, when hunting, walk forward until their antennae touched a desirable object ; then, with wonderful speed, they would swing the abdomen sidewise at a very sharp angle until the forceps were where the antennae had been, when they would instantaneously snap the prey if it had not escaped. If it had, the earwig, with scarcely a moment's delay, would continue its expedition, (c) Earwigs also use their forceps in mating. Although these forceps are so strong, they are yet very sensitive. One earwig can hardly touch with its antennae the forceps of another without the second one immediately knowing it. When mating, the two earwigs, after
er, ~ P P ~ O ~ C ~ I each other
/




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ement chase
rwig~, which
[enerally no
;ep. When
ad caught it
ok the shape
prey, Then
IW also seen
'xma place to
have chased
that in their
their progress
br sand-fleas in
; forward until
id, they would
{ere where the
y if it had not
Id continue its
a these forceps
touch with its
:ly knowing it.
ach each other
53
ch. Then the malecompletely inverts the end of s to back under the fema
The forceps of the male and of the female differ, as we have already noticed, those of the male being the more rounded and irregular. (The original type seems to have been that of the female, for both sexes have this type until the last stage.) The shape of the male forceps also varies greatly, male differing from male (see .
Figure I, a and c) in a marked manner, while that Oå the female is always the same. I wondered at first why the forceps of the male should be curved as they are. I noticed that the rkht one frequently laps a little over the left when they are closed, and that it is usually a little more bent than the left. When I saw that the male in mating, inverts his forceps and that therefore the right is the one to touch -
the ground, I could readily see at least one advantage in the present shape. The right is the more bent of the two, often with the point at right angles to his body, or sometimes even pointing a little forward. It would, therefore, not offer the obstruction to his backward movement that it would It his forceps were shaped like those of his mate. This applies certainly to the earwig which I had in confine- ment.
Still so great is the difference both in shape and di Ie applicable to all.




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