But few words are necessary to indicate the importance of entomology,
especially to the farming community; for while insects play a most
important part in the economy of nature and furnish us some valuable
products and otherwise do us a great deal of indirect good, yet they are
chiefly known by the annoyances they cause and by the great injury they
do to our crops and domestic animals. Hence some knowledge of insects
and how to study them becomes important, almost necessary, to every
farmer.
The scope of the science may best be indicated by a statement of the
number of species existing, as compared with other animals. The
omnipresence of insects is known and felt by all; yet few have any
accurate idea of the actual numbers existing, so that some figures will
not prove uninteresting in this connection. Taking the lists of
described species, and the estimates of specialists in the different
orders, it is safe to say that about thirty thousand species have
already been described from North America, while the number of species
already described or to be described in the Biologia Centrali-Americana,
i. e., for Central America, foot up just about the same number, Lord
Walsingham having estimated them at 30,114 in his address as president
of the London Entomological Society two years ago, neither the
Orthoptera nor the Neuroptera being included in this estimate. By way of
contrast the number of mammals, birds, and reptiles to be described from
the same region, is interesting. It foots up 1,937, as follows:
Mammals, 180; birds, 1,600; reptiles, 157.
If we endeavor to get some estimate of the number of insects that occur
in the whole world, the most satisfactory estimates will be found in the
address just alluded to, and in that of Dr. David Sharp before the same
society. Linnaeus knew nearly 3,000 species, of which more than 2,000
were European and over 800 exotic. The estimate of Dr. John Day, in
1853, of the number of species on the globe, was 250,000. Dr. Sharp's
estimate thirty years later was between 500,000 and 1,000,000. Sharp's
and Walsingham's estimates in 1889 reached nearly 2,000,000, and the
average number of insects annually described since the publication of
the Zoological Record, deducting 8 per cent for synonyms, is 6,500
species. I think the estimate of 2,000,000 species in the world is
extremely low, and if we take into consideration the fact that species
have been best worked up in the more temperate portions of the globe,
and that in the more tropical portions a vast number of species still
remain to be characterized and named, and if we take further into
consideration the fact that many portions of the globe are yet
unexplored, entomologically, that even in the best worked up regions by
far the larger portion of the Micro-Hymenoptera and Micro-Diptera remain
absolutely undescribed in our collections, and have been but very
partially collected, it will be safe to estimate that not one-fifth of
the species extant have yet been characterized or enumerated. In this
view of the case the species in our collections, whether described or
undescribed, do not represent perhaps more than one-fifth of the whole.
In other words, to say that there are 10,000,000 species of insects in
the world, would be, in my judgment, a moderate estimate.