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The cubital cells are never less than three with the
TenihredinidcB, but may be two only with Oryssus.
When there are three cubitals, either the first or
second may be the longest. The first is small with
Dolerus and Cryptocampus, large with Emphytus,
Cladius. If small, it never receives a recurrent ner-
vure, but in the other case it may receive one only or
two. If the first is small the second always receives
two nervures. When there are four the first is small
and never receives a nervure, but the second and third
receive one each, or the second may receive both, e.g.
Nematus.

On the lower side of the wing, between the median
and anal cellules, and bounded by the anal nervure
above and the accessory beneath, there is an elongated
cellule called the lanceolate cellule, which is of great
value in classification ; and it is moreover peculiar to
the Tenthredinidce. According to the position of the
accessory in relation to the anal nervure, the cellule
assumes four different forms.

I. The accessory nervure issues from the middle of
the cellule, where it curves down from it, to unite with
it again at the end, thus forming an elongated, sharply-
pointed cellule at the end. This is called a petiolated
lanceolate cellule, and it occurs with the following
genera : Nematus, Dineura, Schizocera, Fenusa, Blen-
nocampa (PL X, fig. 12 d).

II. The accessory nervure unites with the anal not
far from its origin, then breaks off, but issues again
from the anal nervure towards the middle, when it
curves down to become united with it at the end.
There are thus two unequal cellules formed, a small



!



POSTERIOR WIXGS. 13

one at the base and a larger one at the apex. This is
a contracted lanceolate cellule, and is possessed by
Zarcea, Abia, Amasis, Hylotoma, Monoctenus, Cladi*,
Camponiscus, Hemichroa, Hoplocampa, Macrophya (in
part), Syncerema (PI. X, fig. 12 e).

III. The accessory nervure touches slightly the
anal in the middle, thus forming two cellules of
nearly equal length. To this form the term subcon-
tracted has been applied, and we meet with it in
Pachyprotasis, Macrophya in part (PL X, fig. 12 b).

IV. The nervure does not touch the anal nervure at
all ; this form may be either open or closed. It may
be closed by

(a) An oblique cross nervure placed beyond the
middle of the cellule as in Dolerus, Emphytus, Phyllo-
toma, Eriocampa, Athalia, Taxonus, Poecilosoma,
Tarpa, Lyda, and Pinicola (PL X, fig. 12 a), or by

(b) A straight cross nervure in the centre of the
cellule as in Tenthredo, Tenthredopsis, Allantus, Cimbex,
Trichiosoma, Clavellaria, Lophyrus (PI. X, fig. 12 c).

(c) Without any cross nervure, as in Selandria,
Strongylog aster in part, and Aneugmenus (PI. X, fig.
12).

The posterior wings have never a stigma, but may
have an appendicular cellule (Hylotoma). They are
divided into cellules like the anterior, but they are
fewer in number and in importance.

The most important feature in classification is the
presence or absence of the transverse cubital (PI. X,
fig. 1 g, lower wing) and recurrent nervures (fig./). If
absent the inner cubital cellule (fig. 5) becomes con-
fluent with the outer (fig. 6), and the discoidal (fig. 8)
with the posterior (fig. 9). Generally both nervures
are present, but with Monophadnus, Harpiphorus,
Poecilosoma, the transverse cubital is absent, and the
recurrent present ; while with Emphytus, Fenusa, Phyl-
lotoma, Blennocampa, Taxonus, neither is present.
According as these nervures are absent or present, the
species are said to have no middle (or discoidal)



14 THE ABDOMEN.

cellule (as in JEhnphytus), one as in Poecilosoma, or two
as with Tenthredo, &c.

Specific characters, too, are sometimes afforded by
the position of the nervures. In this respect the form
of the accessory nervure is often useful. Sometimes it
is received at a greater or less distance in front of the
transverse median nervure (called then appendiculated)
(PI. X, fig. 13), or it may be joined to the transverse
median (PL X, fig. 13 a), when it is said to be inter-
stitial.

The posterior wing has, on the costa, a number of
hooks, which fit into the thickened brim of the lower
edge of the front wing, so that in this way the two
remain united in flight.

It only remains to add that with individual speci-
mens of most species, one or other of the cross ner-
vures may be absent, while, less frequently, greater
aberrations are met with. The species of Dineura (and
the Nematina generally) are especially liable to vary in
this respect ; with D. stilata, for instance, the trans-
verse radial nervure is as often absent as present.

In the radial, cubital, and transverse and recurrent
nervures, are usually found small, white, blistered
spaces, which have been called by Walsh "bullae."
These exist in other groups of Hymenoptera ; and in
the Ichneumonidce have been shown by Walsh* to have,
from their constancy in position, some value from a
systematic point of view. They do not, however,
appear to have an equal value in the Tenthredinidce,
although in some cases they would seem to differ in
position in closely allied species or genera, and conse-
quently their presence or absence is worth mentioning
in specific descriptions, or even in generic ones.

The Abdomen.

The abdomen is joined to the thorax by its entire
width. It is, as a rule, longer than the head and

* Proc. Ent. Soc. Phil., v, p. 209, and vi, p. 242.



. THE ABDOMEN. 15

thorax, but may be shorter. It is never quite cylin-
drical, being usually somewhat flattened above and
beneath. With Selandria it is ovoid, is longer and
more rounded with the Tenthredina, and much flat-
tended with Lyda. With the Tenthredinaitbvlgea out
in the middle : Cimbey has the dorsal surface some-
what arched, curved down towards the apex, and the
belly flattened with the sides sharp. A few forms
have the apical segments much contracted. On the
apex of the eighth (or ninth, counting the fourth
segment as abdominal) segment (which has sometimes
no dorsal arc) are two unjointed projecting organs,
called cf'Tcl. They are seldom very conspicuous, but
with Cryptocampus, &c., they are very prominent.
What may be their use is still an unsettled ques-
tion, but probably they act" in some way as tactile
organs.

The separation of the abdomen from the above-men-
tioned fourth thoracic segment is usually marked by
a transverse incision, covered with a white membrane,
which with Cimbex and many other genera is very
conspicuous, and is called the blotch (nuditas}. The
abdomen thus, according to the above view, consists
of eight segments. Of course, if the fourth is to be
regarded as abdominal, the number would be nine,
and certainly the fourth has every appearance of
forming part of the abdomen, if we neglect other
considerations.*

While, as has been said, the last segment is not at
all, or but slightly, developed above, below it forms
two oval or oblong plates, cleft in the middle (PI. X, fig.
5 1, 3, PI. X, fig. 4, 8), which are called the hypopygial
wlces. They are seldom of great size, rarely occupying
one fourth of the length of the abdomen, except with
those species, e.g. Nematus luteus, which oviposit in
twigs, and consequently require a long and strongly-

* As a matter of convenience, and to facilitate comparison with
Continental works, in the descriptions I have counted the number of
segments as nine.



16 THE OVIPOSITOR.

built ovipositor. In that case it occupies the apical
half of the abdomen.

The ovipositor proper consists of a pair of flattened,
broad, lancet-like organs, generally somewhat curved
towards the apex, and of a firm horny consistency.
Bach pair is composed of two distinct parts, viz. a
back piece or support (PI. X, fig. 5 a), and the
cutting instrument proper. The support is, as a
rule, very much stouter in texture than the "saw' :
itself. It is slightly hollow on one side, while on the
lower edge there is a thickened rim, by means of
which the " saw " is attached to it. At the base it
is much thicker than at the apex, while the colour
there is darker. On the surface of the support, as it
may be called, are not unfrequently a number of
transverse bars, readily noticeable by their deeper
colour. With most species these transverse bars are
simple, but occasionally they are armed with minute
teeth, e.g. Hylotoma, Nematus luteus. The support may
be (and this is more often the case) of the same shape
as the saw, but may be different, as in, e.g. Gintbex.

The lower edge of the saw bears projecting teeth,
which may be simple projections somewhat like the
teeth of a hand saw, or these projections may them-
selves be armed with minute teeth-like indentations.
In Cimbex the edge is provided with little bead-like
projections, arising at the base from a pedicle, and
covered all over with minute teeth. Like the support,
the saw bears a number of transverse bars, distin-
guishable by their darker colour, and either un-
armed or minutely toothed (Cladius). Thus, the
saw (to quote Newport's illustration) is, in its most
advanced state, a lance, a saw, and file all in one, for
there is no doubt that the teeth on the bars serve as a
file. The structure of the saw and its support has a
direct relation to the work they have to do. Thus,
those species which deposit their eggs in twigs or
young branches have the ovipositor very stout, broad,
and well armed with teeth, e.g. Hemichroa rufa,



THE OVIPOSITOR. 17

Cladius viminalis, Hylotoma rosce, and Nematus luteus ;
while, contrariwise, wlien the eggs are laid in the
leaves they are slimly built, with the teeth and bars
not well developed, e.g. Nematus miliaris, or may be
scarcely represented, as with Nematus ribesii, which
simply glues the eggs to the leaf without making any
cutting.

Outside the saw and its support, and serving as a
protecting case to them, is a two-jointed organ, which
projects to a certain extent out of the last abdominal
segment. The outer joint of this case is, as a rule,
differently coloured from the basal portion, is much
thinner than it, and hairy at the apex. At the base
the inner side is lengthened out, so as to follow the
curve of the basal joint, while at the apex it is rounded,
but not very sharply (PI. X, fig. 5).

At first sight the basal joint looks as if it were
composed of one piece, but on dissection it is seen to
be composed of two. The main piece is longer than
broad, and curved to a point at each end, the lower
end being the sharpest. At the outer end of the
upper part is, firmly attached, a triangular plate,
which joins the whole to the base of the eighth abdo-
minal segment (PI. X, fig. 5, 1), the basal part being
thus composed of two pieces.

The saw and the back piece are joined to the above-
described plates in the following way : The support
is attached, on the one hand, by its curved base to
the middle of the oblong plate on the inner side (fig.
4), while from its thickened rim there proceeds, not far
from the base, a thin wire-like structure, which goes
round the top of the " oblong " plate, to which it is
firmly attached close to the above-mentioned smaller
piece (fig. 5, 3). In a similar way a wire-like projection
proceeds from the base of the saw, above that of the
support, and fixes the saw to the triangular plate, but
it is not attached otherwise, save, of course, to the
support.

The basal half of the sheath thus not only serves as

VOL. i. 2



18 THE ANAL APPENDAGES.

a point of attachment to the saw, but it may be also
said to support its outer valve, which is only loosely
attached to it, and consequently is capable of being
moved about by the insect with some freedom. It
undoubtedly serves as a sheath to protect the apical
part of the saw, but I believe it acts also, in some way,
as a tactile organ.

The ovipositor, then, is composed of three pairs of
organs, or six pieces in all, the two-jointed outer
sheath, the support, and the saw itself. The saws are
joined near the top, and on the lower side, by a
muscular band, but the connection between them is
often not very close. They are thus capable of being
separated, and form a passage for the eggs to go
down. Above the saw may be seen a pair of chitinous
processes, between which the tube of the poison gland
enters.

The Male Anal Appendages.

The last abdominal segment projects on the lower
side and forms a kind of hollow, in which the male
genital armature lies. Like the female organs, they are
easily extracted, and are of a tough, horny, or leathery
texture. At the base is a thin ring (PI. XV, fig. 14,
3), by means of which the parts are brought into con-
nection with the inner sexual organs. The parts next
to this ring are two double- jointed valves, united by
membrane at the base. They are curved round on
the inner side so as to form a hollow tube, in which
the double-valved penis lies (PI. XV, fig. 14, 2, and
fig. 14 a), forming, in fact, a sheath for it. The basal
part is hard, horny, glabrous, and deep brown in
colour. The apical portion is much smaller, more
membranous, lighter coloured, and hairy externally
(fig. 14, 1) ; it is usually somewhat triangular or oval
in shape, and possesses some flexibility. The shape
of the organs may be seen by reference to the figures
(PL XV, fig. 14).



THE AXAL APPENDAGES. SPIRACLES. 19

The male anal appendages undoubtedly might be
made to furnish specific characters, but they are very
minute, and difficult either to describe or figure, so I
have not mentioned them in the descriptions of the
species.

The spiracles are nine in number. The first is
placed on the prothorax, close to its union with the
mesothorax, and a little way down from the tegulas.
The second is on the metathorax, close to the meso-
thorax ; the rest are on the first to seventh abdominal
segments. They are always placed on the front of
the segment, and on the abdomen are situated on the
upper edge immediately below the back.

With the larvae the first segment bears a spiracle ;
the next is on the footless fourth segment, the rest on
segments five to eleven.

The outer covering of the imago is generally smooth
and somewhat shining, rarely is it punctured to
any extent. A few forms have hairy bodies, e.g.
Trichiosoma. Many (especially exotic species of the
Hylotomina) have their bodies of a decided metallic
lustre.

As for colour, it is generally black or some shade of
it. Some are coppery-green or blue ; a few green
without any metallic reflection, e.g. Tenthredo punc-
tulata ; yellow or some shade of it is not uncommon
with Nematina and Hylotomina. The legs are often
differently coloured from the rest of the body ; red is
a not uncommon colour for them, and, as a rule, the
tarsi are black, or darker coloured than the other
parts. The antennse may be either uniformly coloured
or paler on the under side, more rarely they are orna-
mented with white rings.

There is one curious point about the coloration
pattern in these insects which deserves notice, namely,
that many species belonging to widely separated
genera are coloured alike. Especially is this the case in



20 COLORATION.

the neotropical region, where two forms of coloration,
rare in Europe, are very common, there being scarcely
a genus without an example of the two patterns. In
one case the body and wings are black, or bluish-black,
and the prothorax and, it may be, part of the meso-
notum, red ; in the other the ground colour is yellow
with black on part of the thorax, and the wings yellow,
with two or more broad black bands. Of the first
class we have two or three British examples, of which
Blennocampa eppiphium is the best known. As the
insects having this form are broad compared to their
length, and as they have the habit of folding the wings
and of pressing the antennge and legs close to the body,
and dropping to the ground, where they remain motion-
less as if dead, it is possible that the red on thorax may
aid in concealing them. The other type of coloration is
a common one with terebrant Hymenoptera in South
and Central America, and I suspect it has some refer-
ence to the flower-frequenting habits of the insects.

Secondary Sexual Characters.

Apart from the internal or primary sexual characters,
there are more or less well-marked secondary distinc-
tions between the males and females. These differ-
ences may be grouped under six heads, it being
premised that in all cases the males are smaller, and
of a slighter build than the females, while the abdomen
is flat, seldom or never cylindrical.

1. Coloration. The general rule is that the males
are darker and more obscurely coloured than the
opposite sex, while their specific characters are much
less well marked. In many luteous species of Nematus,
for example, the males have the upper surface of the
body black ; in others, e.g. Macrophya, they want the
white, yellow, or reddish markings, which the
females have on the legs, thorax and abdomen. Many
species show no distinction in colour between the 1
sexes, while in others it is extreme. Thus with



SECONDARY SEXUAL CHARACTERS, 21

Hemichroa alni the ? has the head and thorax for
the greater part red and the legs black, while the
cj has the head and thorax black and the legs
testaceous. On the other hand, there are species which
have the males lighter coloured than the females.
This is the case with Nematus rumicis, Heptamelus
ochroleucus, Tenth-redo zonata, T. velox, 8fc.

2. The eyes. The most noteworthy difference in the
eyes is with the <? of Alia, in which they are con-
fluent, or nearly so, at the top of the head, although in
the normal position with the ? .

3. Month organs. In Cimbex, Trichiosoma, and
especially Clavellaria, the mandibles in the male are
very largely developed, projecting, and strongly
toothed.

4. Differences in the structure of the legs. In
Trichiosoma the hind femora are grooved on the lower
side, each end of the groove at the apex terminating in
a blunt tooth. In Gimbex the patellae are well deve-
loped, and at the base of the basal one there is a pro-
jecting spine. In the same genus there are blunt,
short spines on the coxae, which are themselves very
large, and projecting. Some species of Allantus and
Tenth-redo have the legs in the rf (especially the hinder
pair) much longer than in the ? , and the tarsi and
base of tibiae thickened, while in Tenthredo zonata,
besides these differences, the tarsi on the under side,
are provided with closely pressed velvety pads of hair.

5. Antennce. With the majority of saw-flies, the
antennae merely differ in being a little longer or
thicker, or in having the joints more compressed.
But with the Lophyrina they are very dissimilar, being
either deeply biramose as in Lophyrus, or with only
one row of pectinations as in Monoctenus and Clado-
macra. The same is the case in a less degree with
Cladius. In Schizocera and other Hylotomina, they are
furcate or cleft in two, like the prongs of a fork, the
joints being either densely covered with long hair, as
in Sericocera, or bare and grooved as with Dielocera.



22 SECONDARY SEXUAL CHARACTERS.

Many widely divergent species have them densely
pilose, e.g. Oladius padi, Nematus lucidus, Blenno-
campa aterrima. In Peranthrix the terminal joint has
a stiff bristle. Not a few have the third joint curved
in the c? . The species which have flabellate antennae
in the males, have heavy, thick-bodied females, which,
according to my experience, are very sluggish in their
habits.

6. In the ivings.-^-Tliis is a rare occurrence. The
most interesting peculiarity occurs with Perineura,
Synaerema, Blennocampa with a few species, Erio-
campa Cinxia, and Taxonus agrorum, in which the
apical cross nervures are situated at the apex of the
wing, so as to form a continuous border round it,
while with the females they are in the nor malposition,
i.e. in the middle. The median cellules, therefore, do
not exist, properly speaking (PI. VIII, fig. 10, PI. XI,
fig. 6 a).

Habits of the Perfect Insects.

In the perfect state saw-flies live but a very short
time generally only a few days. They abound mostly
during the months of May, June, and the early part of
July, and with the second broods at the end of July
and in August. As a rule they are very sluggish in
their habits. Their flight is weak and heavy, and they
never fly far at a streteh ; usually they alight after a
flight of ten to twelve feet, and unless engaged in lay-
ing their eggs it is only in the sunshine that they fly
much, nor do they rest long on any particular spot
when the weather is warm. During dull weather, and
after the sun has set, they rest almost motionless on the
leaves of plants, &c. The species of Lyda are very
active during hot sunny days. Many species frequent
flowers, partly for the purpose of feeding on the pollen,
but also, in the case of Tenthredo and Allantus, in
order to prey upon Meligethes, Byturus, and other
insects found in such situations. The plants which



HABITS OF IMAGOS. 23

they are most partial to are Ranunculacece, Umbel-
liferce, Rosacece, and Compositce. The flower- visiting
species belong mostly to Tentkredo and Allantus ; next
in order we have Hylotoma, Cephas, Athalia, Dolerus >
and last of all Nematus, which are very seldom found
on flowers. Selandria serva is often seen on Umbel-
liferce; Tarpa on Compositce; Abia on UmbeUiferw and
Compositce ; Tenthredo Hvida I have noticed to have a
partiality for Rubus idceus ; various species of
Dolerus (which are the earliest in the season to appear)
are not uncommonly observed on willow catkins. I
have a specimen of Atlialia hcematopus (a South-
African species) with pollinia of an orchid attached
to the fore tarsi.

Many of the smaller species especially those of
Blennocampa, Fenusa, and some of the smaller species
of Nematus, have a habit, when alarmed in any way, of
tucking the antennas, legs, and wings, close to the body,
and falling to the ground as if dead ; and often they
remain some minutes in this position before making an
attempt to escape. This seems to be the only peculiar
method they have of escaping from their enemies,
except the usual ones of flight, &c., and, in the case of
Trichiosoma and other larger forms, of using the
mandibles on whatever attacks them.

Beyond depositing the eggs in the proper nidus, the
females, in the great majority of species, take no
further care of their progeny, and generally die imme-
diately after oviposition. An interesting exception to
this is found in the case of a Tasmanian species of
Perga (P. Leioisii, W.), which deposits its eggs in a
longitudinal incision between the two surfaces of the
leaves of an Eucalyptus, close to the midrib, arranged
across in a double row, there being about eighty eggs
in all. The mother sits over them with outstretched
legs, and when the larvse make their appearance she
follows them, defending them with great assiduity from
the attacks of Ichneumons and other enemies.

I am not aware of any internal parasites attacking



24 HABITS OF IMAGOS.

them in the perfect state except fungi. Nor do they
seem to have any special external enemies. Birds I
have never seen feeding on them, but have often
witnessed combats between them and ants, carnivorous
beetles, and centipedes.

The males appear five or six days in advance of the
females. The union of the sexes generally takes place
in the sunshine. It lasts only for a few minutes, after
which the female gets restive and kicks off the male,
who dies in a few hours after, while the female imme-
diately proceeds to deposit her eggs. From the struc-
ture of the copulatory organs, the <$ has to insert
them backwards ; and sometimes one may be seen
dragged about by the ? , attached only by the anal
appendages.

So far as my observations go no selection is shown
by either sex in choosing partners. With Trichiosoma
I have noticed that the males, after emerging, and
apparently before the females have appeared, assemble
together on the tops of birches (with T. lucorum), round
which they fly in circles in the hot sunshine, making
as they do so a loud buzzing noise, not unlike the
humming of a Bombus. They do not fly far, and gene-
rally return after a short flight to the tree top from
which they started. I was once the witness of a
battle between two males of T. lucorum, which lasted
for nearly ten minutes, or perhaps longer, for they
flew away, and may have continued the fight after I
lost sight of them. Their mode of fighting was simply
to fly at each other in the air, a concussion of the two
bodies being the result ; and they must have come



Online LibraryPeter CameronA monograph of the British phytophagous Hymenoptera .. (Volume 1) → online text (page 2 of 31)