Samuel Wendell Williston.

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MANUAL



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^ORTH American Diptera



BY



SAMUEL W. WILLISTON



Third Edition



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NEW HAVKN
JAMES T. HATHAWAY

297 CROWN ST. NEAR YALE COLLEGE
1908



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Copyright, 1908,

BY

SamukIv W. W11.1.1STON.



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PREFACE.

Twenty-four years ago the writer began the publica-
tion, in the Bulletin of the Brooklyn Entomological
Society, of a series of synoptic papers on the families and
genera of North American Diptera, Previous to that
time but seven of the sixty odd families had thus been
rendered accessible to the American student in the works
of Loew and Osten Sacken. In 1888 these synopses
were revised and published, with others, in a pamphlet
of 88 pages entitled ' Synopsis of the Families and
Genera of North American Diptera, exclusive of the
Nematocera and Muscidse.' It contained tabular defini-
tions of about three hundred and fifty genera, all at that
time known from the United States in the families treated.
In the succeeding eight years the writer's acquaintance,
especially with the southern forms, had been so widened
that he attempted a similar review of all the North and
Middle American genera, aided by Professor Aldrich in
the Dolichopodidse and Mr. Snow in the Ortalidse. Re-
gretfully the very large and almost chaotic families
Dexiidse and Tachinidae were not included. Eight hun-
dred and twenty-six genera were defined in this 'second
edition' more or less accurately, very nearly all of which,
save those of the Dolichopodidae, had been studied by
the writer in its preparation. The continued use of this
work, both in America and abroad, has been very grati-
fying to the author, a use that has made him the more
desirous that a better and more complete edition should
be prepared, one that would be of greater service to the
amateur, whose interests have been paramount. For such
an edition the present time seemed opportune, since the
recently published catalogue of the Diptera of North



4 NORTH AMKRICAN DIPTERA.

America, by Professor Aldrich, a very meritorious work,
has lessened materially the labor of its preparation, and
must add to its usefulness. It was with some misgivings,
however, that the author undertook the no inconsiderable
task, since his studies for some years past have been
almost wholly in a widely different field from that of
entomology — vertebrate paleontology, a subject which,
indeed, has absorbed the larger share of his attention
for the past thirty years.

But, he would not have undertaken the task, save
upon the kind assurance of assistance and contributions
by several of the leading students of diptera in the United
States. The chief progress during the last twelve years
has been in comparatively few families, the most of which
had been but indifferently well studied at the time of the
publication of the second edition; a progress in large part
due to the work of the present contributors.

Professor C. F. Adams has kindly aided in a large
part of the work, especially the Cyclorrhapha, though
the writer assumes all responsibility for changes and ad-
ditions not directly accredited to the several contributors.
Professor Adams has also furnished the tables for the
very difficult families Dexiidse and Tachinidse, omitted
in the previous edition. As in the former edition, the
characters and table of the Dolichopodidae are wholly
the work of Professor Aldrich; he has also generously
assisted in other wa3^s, and it need not be said that, with-
out the aid of his Catalogue, the labor of revision would
have been greater, and the results less satisfactory.
Mr. C. T. Brues, who has given so much critical attention
to the singular family Phoridse, has furnished the char-
acters and table of that family; one needs to compare his
table with that of the former edition to see how much has
been done in that group. Professor James Hine has re-
vised the characters and table of the Tabanidae. Professor



PREFACE. 5

O. A. Johannsen has furnished a new table of the Chiro-
nomidse. Professor V. L. Kellogg has done the same for
the Blepharoceridse, and has revised the family charac-
ters. Professor A. L. Melander has treated the Kmpididse
anew; and Professor C. H. T. Townsend has generously
criticised the figures of the Dexiidse and Tachinidse, and
has furnished important notes on many of the genera.
To all these gentlemen the author tenders his sincerest
thanks, not only on his own part, but also on the part
of those who will have occasion to use the work.

At the outset it was not contemplated to give many
illustrations, chiefly such as would be explanatory of
the more important characters. In the end more than
six hundred genera have been defined more or less fully
and decisively by nearly one thousand figures. Of these
figures all those of the Dolichopodidse and the first plate
of those of the Tachinidse were furnished by Professor
Aldrich. Mr. Brues has furnished the figures of the Phori-
dae. Professor Hine those of the Tabanidae, and Professor
Melander most of those illustrating the Empididae. Pro-
fessor Washburn kindly gave permission to use electro-
types of twenty-three figures prepared for his or the late
Professor Lugger's reports on Minnesota Diptera. To
Professor Kellogg and Henry Holt & Co. the writer is
indebted for eight electrotypes of figures in Professor
Kellogg's American Insects; and to Professor J. B. Smith
his thanks are due for six figures of the Culicidse, orig-
inally prepared for his Report on the Mosquitoes of New
Jersey. A few other figures have been copied from relia-
ble sources, where specimens were not easily accessible,
and are likewise credited in each case to its author. All
the remainder, whether drawings or photographs, more
than eight hundred in number, have been made by the
writer from specimens — a task which has involved many
months of labor, but which could not, in most cases, have
been safely entrusted to a professional draftsman.



5 NORTH AMERICAN DIPTERA.

To the authorities of the National Museum and Mr. D.
W. Coquillett, the writer is indebted for the communica-
tion of specimens of fourteen genera for purposes of illus-
tration. Finally he has to express his hearty thanks to
his friend and former colleague, Dr. F. H. Snow of the Uni-
versity of Kansas, for the free permission to make use of
whatever specimens were needed in the rich collections of
that University — collections which include nearly all the
types of diptera from the United States described by
Townsend, Snow, Adams and the writer.

Since the preparation of the present edition w^as begun
has occurred the death of one whose name will ever be
honorably associated with American Dipterology, Dr. C.
R. Osten Sacken. The author can not forbear placing
on record here an earnest tribute of friendship and ad-
miration for the man, and unqualified appreciation of
his work as an entomologist. His constant encourage-
ment and kindly criticism during a correspondence of
more than twenty 3^ears have made this book, whatever
be its merits, possible; and the author only hopes that it
may be found not unworthy of association with his work.
It is with pain, also, that the author here records the
death, in early years, of his friend and student the late
Mr. W. A. Snow, who assisted in the preparation of the
Ortalidae of the former edition.

About twelve hundred genera are defined in the pres-
ent edition, with the exception of a few doubtful forms,
all those known from North and Central America and
the West Indies. That the definitions are wholly with-
out error is inconceivable. Whatever revision the book
may receive in the future must be left to others, and,
in taking final leave of it after these twenty-four years,
the writer will be pardoned in repeating the words of a
master, one whose works have served as models for this,
Rudolph Schiner:

'Unci so uebergebe ich denii diese nieine Arbeit der OeffentHchkeit
mil dem Wunsche, dass sie billigen Anfordernngen entsprechen inoege
und mil dem Beifuegen, dass ich dem Urtheile unparteiischen L/eser
mit voller Beniliigung entgegensehe, da ich bewusst bin, bei lyoesung
meiner Aufgabe mit allem Eniste nnd der groessten Gewissenhaftig-
keit vogegangen zii sein.'

SAMUEL W. WIIylvISTON.

University of Chicago, June, 1908.



CONTENTS.



Introduction ....
Structure and habits of flies
Morphology

Head .

Mouth-parts

Antennae

Thorax

Legs .

Abdomen .

Wings !

Vestiture .

Chsetotaxy

Internal anatomy
Classification of diptera
Collection and preservation of



flies



Group characters and synoptic table or the eamiues of

DIPTERA

Famii^y characters and synoptic tabIvES of genera



I


Tipulidae


II


Psychodidse


III


Dixidae .


IV


Culicidse


V


Chironomidae


VI


Cecidomyidae


VII


Mycetophilidae


VIII


Bibionidse


IX


Simuliidae


X


Blepharoceridae


XI


Orphnephilidae


XII


Rhyphidae


XIII


Leptidae .


XIV


Stratiomyidae


XV


Acanthomeridae


XVI


Tabanidae


XVII


Cyrtidae .


XVIII


Neniestrinidae


XIX


Apioceridae



9
i6
20
20

24
27

31
34
36
37
43
45
49
51
62

65

81
92

94

96

no

117

131
140
144
148
153
155
157
164

173
176
182
186

188



8



NORTH AMERICAN DIPTKRA.



XX

XXI

XXII

XXIII

XXIV

XXV

XXVI

XXVII

XXVIII

XXIX

XXX

XXXI

XXXII

XXXIII

XXXIX

XXXV

XXXVI

XXXVII

XXXVIII

XXXIX

XIv

XLI

XLII

XLIII

XlylV

XI.V

XL VI

XIvVII

XLVIII

XLIX

L

hi

LII

IvIII

LIV

LV

LVI

LVII

LVIII

LIX

LX

LXI

Appendix

Index



Mydaidae

Asilidse .

Therevidse

Sceiiopinidae

Bombyliidse

Empididae

Dolicliopodidae

Phoridse .

lyonchopteridse

Platypezidse

Pipunculidse

Syrphidae

Conopidae

Tanypezidae

Micropezidae

Psilidae .

Sepsidae .

Ortalididae

Rhopalorneridae

Tr3'petidae

Saproniyzidae

Agromyzidae

Geomyzidae

Drosophilidae

Ephydridae

Oscinidse

Diopsidae

Borboridae

Phycodroniidse

Heteroiieuridae

Scioiiiyzidae
Heloniyzidae .
Cord3duridae .
Aiithoiiiyidae .
Muscidae
CEstridae
Sarcophagidae
Dexiidae .
Tachinidae
Hippoboscidae
Streolidie
Nvcteribiidae



190
192
205
208

2IO
218
228

240
241
244
246
261
264
264
267
269
271
280
282
288
291
297
299

303
310

314
315
317
318
321
324
327
331

337
344
348
352
358
382

384
386

387
391



NOETH AMERICA!^ DiPTERA.



INTRODUCTION.

The order of two-winged insects known as flies or Dip-
tera includes more than forty thousand known species
from different regions of the world. Since many of the
species are small, or even minute, and inconspicuous,
and since the order as a whole has not received the at-
tention from collectors and students of entomology that
other and more attractive groups have, it is very certain
that many more await discovery. A very reasonable es-
timate would place the entire number of species of flies
at present in existence at more than eighty thousand.
From North America the recent catalogue of Aldrich
gives a list of about eight thousand species, distributed
in more than a thousand genera. The subject is a wide
one and replete with interest.

To the student beginning the study of this interesting
order of insects a few words of advice or caution Vlislj not
be superfluous. The present work can make no preten-
sions to completeness in the characterization of genera,
at least in the majority of cases; that would require
a work many times larger than is the present one, and is
practically' impossible at the present time. One must
not, therefore, depend entirely upon tables and figures
in the absence of other information and other assistance,
especially when he knows but few forms. If he does not
immediately succeed in securely locating his specimens



lO NORTH AMERICAN DIPTERA.

he should nolf too hastily conclude that they are 'new'.
Until he has acquired a considerable acquaintance with
different families, the work of classification may at times
be tedious, but by perseverance he can not fail to over-
come whatever obstacles families and genera may pre-
sent. He will be very much aided at the beginning by
having a tolerabl}^ large collection at his command with
which to make comparisons. Difficulties to the inexpe-
rienced will often disappear with positive evidence before
him, when negative characters would be doubtful. With
each genus in a family positively determined, the diffi-
culties and uncertainties of others will gradually disap-
pear. Better still if he has numerous species reliably
named with which to begin his studies. The present
writer in his entomological career had few if any species
or genera determined for him by others, and he well ap-
preciates how wasteful of energies was such a method,
at the time unavoidable. For full generic descriptions
of many, perhaps the larger part, of the North American
genera, the student will find a most valuable aid in
Schiner's Fauna Austriaca, a work of which too much can
not be said in praise. The descriptions are remarkable
for their fullness, accuracy and simplicity, and, although
the work is forty years old, it has lost but little of its value.
To determine his species the student will need access
to a large number of books and papers, lists of wdiich to
the present time will be found in Aldrich's admirable
and indispensable Catalogue of North American Diptera,
published by the Smithsonian Institution. One must
not, however, let the formidable lists frighten him. He
will not need them all to begin with, nor even the larger
part of them, and the earnest student can alwa3^s be as-
sured of the sympathy and assistance of his fellow work-
ers. His earlier determinations, and those of the student
who is concerned chiefly in obtaining a broad general



INTRODUCTION. n

knowledge of the taxonomy of the dipteraj^may be con-
fined, for the most part, to those groups which have been
monographed, with full descriptions of genera and spe-
cies, and, if possible with numerous illustrations. Refer-
ences to the more important papers of each family will
be found in Aldrich's catalogue.

Long before the student has feached the dignity of
'independent research', he will have learned Vv^ho the
masters of dipterology are ; who have shown the greatest
acumen in the discernment and use of classificatory char-
acters. It will not be invidious to distinguish above all
others Schiner, lyoew and Osten Sacken as writers who
can not be too faithfully studied, too closel}^ followed.
Not that they are infallible ; none are. Indeed an error
of a master is often more instructive than the masterpiece
cf a dullard. One must learn the values of characters in
classification before he can be successful in instructing
others, or in making his discoveries known. And this
knowledge can only be acquired by long and faithful
study of living things and due reflection thereon. The
narrow systematic specialist is looked upon som^ewhat
askance by modern biologists, and rightfully too, but I
have no hesitation in saying, and it is the experience of
many years of study in different branches of natural his-
tory, that the right kind of systematic work calls for the
highest scientific powers of the student. I am aware that
some narrow specialists in other departments of science
will take exception to this statement, but I believe it and
say it for the encouragement of those who may be dis-
suaded from the earnest study of such creatures by the
flippant remark of the shallow minded. But a mere col-
lector of specimens, one who finds enjoyment in getting
the largest number and arranging them in serial form in
his cabinet is not necessarily a scientific student, though
he may have a very pleasant and useful pastime; his la-



J 2 NORTH AMERICAN DIPTERA.

bors are scarcely more important than those of the micro-
tomist who cuts up frogs' eggs and makes pictures of
them. There are no principles too deep, no speculations
too lofty to find application in such creatures as flies, the
too often proletarians of the professional entomologist
even.

Most emphatically I would impress upon all students
of dipterology who undertake the subject seriously, that
the greatest need of modern entomology is monographic
work. Nearly ever}^ family awaits the conscientious
monographer, and such work is that which lasts longest
and acquires most renown. The problems of distribution,
of relationship, of origin, of the effects of environments,
or the meaning and value of characters, can be satisfacto-
rily solved by critical monographic studies only. The
description of 'new species' as mere membra disjecta of
faunas, is scarcely worth the energies of the earnest and
careful student, certainly not as a life vocation, and none
else has an}^ business to write at all. It too easily degen-
erates into a mere roll-calling, a catalogue of the permu-
tations of a few characters, increasing the difficulties for
real students who come afterward. The name that an
insect is known by is of trivial importance, and no one
cares who described it, unless he did it poorly. It will
be a fortunate thing when the search for 'new species'
and the interminably haphazard making of 'new genera'
is done.

Even a cursory glance at some of the tables further on
will convince the intelligent student that the real mean-
ing of man}^ of the classificatory characters is yet imper-
fectly comprehended. But little attention has been paid
to homoplasy or 'convergent evolution', and as all true
classification must depend upon the proper use of genetic
characters, it is apparent that future revisions may ma-
terialh' modify our present conceptions of relationships



INTRODUCTION. 13

in many cases. I can offer no better example of this dis-
regard for phylogenetic and convergent evolution than is
shown in the proposed scheme of classification of the
Cecidomyidse on later pages. The structure and use of
the organs of orientation, — the antennae and palpi especial-
ly, the further comparative study of the ocelli and eyes,
the reasons for the evolution of the wing venation in ap-
parently different systems, the causes of the variations in
the patterns of coloration, the meaning more fully of the
different kinds of vestiture, etc., etc., all need much more
attention than has been given them by the systematist,
and it is he who is best qualified to solve such problems.
One of the first questions that a novice in classification
asks is: What is a species, genus, family? The taxono-
mist's answer to the first of these queries is easy: A spe-
cies is a form of life with all its fertile variants. A mas-
tiff and a grayhound are not distinct species of dogs,
because there exist all possible variations between the
two types, though both have bred true to themselves for
more than three thousand years. But a dog and a fox
are distinct species because there exist no varieties con-
necting the two. If no two specim.ens in a given form of
fly have precisely the same relative lengths of the anten-
nal joints, then the relative lengths of these organs is not
a specific character in that form. If, however, all the
specimens occurring in Massachusetts have a definite
relative length for each joint while these in Kansas have
another, the finst impression is that they belong to dis-
tinct species. If further discovery proves that, in cross-
ing the country between Massachusetts and Kansas, the
lengths gradually vary from one to the other, then we
must consider the eastern and western specimens as mere-
ly racial varieties of a single species. The systematist is
never troubled as to what a species is, if he has all the
material he wants.



14 NORTH AMERICAN DIPTERA.

The answer to the second query, What is a genus? is,
however, a very different matter. Ordinarily we might
appl}^ the same criterion, that groups of species gradu-
all}^ blending together should not be separated into two
or more genera. But this will not suffice, since, because
of the actual presence of the connecting links, the ex-
tremes may vary enormously, far more than in many cases
where the connecting links have disappeared, leaving
the extremes isolated into easil}^ distinguishable genera.
Both convenience and the demands of relationships re-
quire here that such groups be broken up, though it may
and often does entail the result that such genera may be
ultimately distinguishable in their most allied species by
only trivial characters. But the temptation offered here,
especiall}^ to the narrow, perspectiveless specialist, is to
use those same boundary characters, or their equivalents,
as generic characters through the whole family, and the
result is an almost innumerable number of proposed di-
visions. As nearly every species of flies has some plastic
or structural distinguishing character, it is very evident
that we might ultimately reach the absurd result of mak-
ing species and genera ^ coterminous. Between this ex-
treme and the other, the grouping of large numbers of
species into genera, all of which can be distinguished by
decisive, if not important, structural characteristics, there
must be a happy mean. This mean, however, must de-
pend more or less upon the opinions of those best quali-
fied to interpret them. In other words I am tempted to
define a genus as being merely the personal opinion of its
propose?'. By an excessive 'splitting' of genera, broader
relationships are lost sight of, and the tendency is inevit-
able to restore these evidences by the invention of new
group terms to express them. Perhaps no better exam-
ples of these tendencies are observable than in the more
recently proposed classification of the mosquitoes. For



INTRODUCTION. l^

many decades systematists were satisfied to distribute tlie
known mosquitoes in a relatively small number of genera,
genera which could be defined by characters equivalent to
those used in the allied families of diptera. With the great
impetus given to the study of these insects by the discov-
er}^ of their agency in the spread of disease, the genera
have been broken up into many new divisions, until sev-
enty or eighty are now recognized by some students of
the family. In the dearth of striking characters, those
of extreme minuteness have been resorted to, such as the
relative lengths and vv^idths of the scales and their distri-
bution on the body; and even colorational characters
have been called in aid. The obliteration of relationships
thus brought about has rendered the erection of numer-
ous subfamilies necessary, and it is even seriously pro-
posed to elevate the previously accepted subfamilies to
family rank, and the family Culicidse to a superfamily !
And I doubt not that some zealous confrere ma}'' yet se-
riously propose to consider the old family Culicidae as a
suborder! Possibly also, it may be necessary some time
in the future to have a quantitative chemical analysis of
a mosquito before deciding to which genus it may belong.
Now it is very apparent that the importance of the mos-
quitoes in man's economy can have no value in classifica-
tion; that, if the happiness and welfare of every living
being were dependent upon the mosquitoes it could not
affect the classification of the family one whit ; but some-
thing of the sort seems to have resulted.

I will admiit that excessive 'splitting' of genera often
brings to light and tests many differential characters
which otherwise might long remain obscure. Neverthe-
less, convenience is an important end of classification, as
well as the expression of relationships. In days gone by
the profuse maker of genera was ridiculed and the results
of his labors were largely ignored; but I fear even Des-



J 5 NORTH AMERICAN DIPTBRA.

void3^'s shade would turn pale with envy in the contem-
plation 'of some of the proposed genera of the modern
culicidologists.

STRUCTURE OF FLIES.

The word diptera, b3^ which the two-winged flies are
known, signifies two wings, the chief characteristic of
the adult insects. All diptera, if they have any wings,
have but a single pair. The hind pair of other insects is
really represented by a small organ on either side, back
of the true wings, consisting of a short, slender stem,
terminating in a knob. The precise function of these
'halteres' or 'balancers', as they are called, if they have
any, is not known ; that they have a secondarily acquired
use is probable, since they are always in vibration



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