There are few points about which we know less than the causes of
distribution and rarity, although there are certain tolerably well
recognized laws which govern the occurrence of some species in certain
localities. What I mean is that marshy spots, say salt marshes for
instance, attract certain beetles and bugs which are never found except in
such places; certain kinds of flowers attract bees which never appear to
visit any others, but these localities and kinds of flowers occur often at
great distances from each other, and why--given a certain flower you
probably find a certain bee peculiar to it; or given a certain kind of
marsh you probably find a certain beetle, although the localities may be
hundreds of miles apart--I think still awaits explanation. I will give an
example with which I am personally well acquainted. {106} There is a rare
little bee (_Macropis labiata_) which at one time was looked upon as an
extreme rarity, having only occurred three or four times in this country.
Mr. F. Enoch, comparatively lately, took a fair number on the flowers of
the greater loose-strife (_Lysimachia vulgaris_) along the canal at Woking;
now that its food-plant is known, it has occurred in several other places
in numbers, and no doubt wherever the _Lysimachia_ is abundant _Macropis_
will probably occur, but how the little creature has been distributed over
the places where this plant occurs, which are often far distant from each
other, seems to me to be an unsolved problem. Then there is another
puzzling point, and that is the extreme rarity of certain insects. No doubt
in many cases this is due to ignorance of their habits, as it has
frequently happened that species once considered of great rarity have
occurred in abundance when their habits have been discovered, as in the
case of _Macropis_, but there are some cases which do not seem to be
explainable in this way. I will again give an example which has been
specially under my own observation. _Dufourea vulgaris_, a little black
bee, {107} which certainly might not be recognized from its outward
appearance, as there are many which very closely resemble it, is still one
of our greatest rarities, only three British examples having been recorded.
The first was taken by Sir Sidney Saunders at Chewton, Hants, on the
twelfth of August, 1879; this was a male; the second, a female, was taken
by Mr. T. R. Billups at Woking, on the first of August, 1881; and the third
by myself at Chobham (about four miles from Woking) on the first of August,
1891. I believe in all cases these were taken on yellow composite flowers.
The flight and behaviour of the male I caught were so peculiar, as it
wriggled itself into the flower, that I knew at once I had caught a rarity,
and remarked to my companions that I believed I had got a _Dufourea_. I
also hazarded the remark that it was "ten years since it had been taken."
When I got home and looked up the former record it was ten years to a day.
Now there are few places in England that have been better worked for the
bee tribe than the Woking, Chobham, and Weybridge neighbourhood; it has
been worked by experienced men who would see a difference {108} in the
flight of an insect directly. The late Mr. F. Smith, in his day our leading
authority, the Rev. F. D. Morice, than whom no one has probably worked the
neighbourhood more thoroughly, Mr. T. R. Billups, Mr. E. B. Nevinson, and
the late Mr. A. Beaumont, have all been over the ground again and again,
and yet only these two _Dufoureas_! and these taken four miles apart. Here
again is a problem which is very perplexing! What part in nature does this
little rarity play? No doubt like everything else it has its duties, and
its corner to fill, but beyond that one can suggest nothing.
Other bees are often exceedingly abundant in one season and very rare the
next, or they will entirely desert a locality where they have been
abundant, and move somewhere else--the occasional scarceness is due
probably to continued wet weather, which often appears to kill the larvae.
Cold winters seem to have no injurious effect, although at one time they
were thought to determine the scarcity or otherwise of the bees of the
following summer. It has, I think, been clearly shown that larvae can stand
almost any amount of cold, although they succumb to {109} the effects of
mildew produced by wet, but there is often no apparent reason why a well
established colony should migrate to quite new pastures. Sometimes the
proximity of new buildings or the digging up of ground may disturb them,
but I know of colonies that have gone from where I knew them a
comparatively few years ago, and where I can detect no change likely to
have affected them. On the other hand there are colonies which one has
known all one's life and which still go on as strongly or more strongly
than ever--the case quoted under _Anthophora_, p. 63, shows what
persistence there can be in some.
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