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ESPECIALLY
(Under the supervision of
FOR
FIELD
FRED T. THORNE,
COLLECTORS
1360 Merritt Dr., 'El Cajon, Calif., U.S.A.)
COLLECTING (ENEIS NEVADENSIS (SATYRIN.IE)
AND OTHER GENERA ON VANCOUVER ISLAND,
WITH A THEORY TO ACCOUNT FOR HILLTOPPING
by
RICHARD GUppy
The discussion on "hilltopping" butterflies, which has somewhat died
out in recent years, was in 1960 revived in my mind by a rather good
season for (Eneis nevadensis. This butterfly is by all accounts the most
inveterate hilltopper in this part of the world.
The spot in which I collect most of my CE. nevadensis Felder is actually
the top of a ridge, rising quite steeply up from the seashore. It is by a
rough estimate, perhaps 500 ft. high. On the landward side the slope
is much more gentle; from my home it takes me about ten minutes to
walk to the top of the ridge, although the ascent from this point is
probably no more than 200 to 300 ft.
The butterflies are found always along a short stretch of the ridge,
about 50 yards altogether, which I suppose mllst be the highest point.
This area is divided into three "compartments", small clearings separated
by clumps of Arbutus and stunted Douglas Firs. In 1960, for about two
weeks in the latter part of June, I could almost depend on finding each
of these compartments occupied by a male (E. nevadensis, which when
collected, would be replaced by the following day.
If it were not for their stubborn insistence on staying in their chosen
small area, these butterflies would not be easy game by any means. With
most of the more active and wary butterflies, a missed swipe means
that the insect will clear out in a hurry, and give the collector no second
chance. But these hilltop CEneis will circle repeatedly; often the collector
is able to get in five or six successive tries, and even if he finally frightens
the butterfly off, only a little patience is needed; in ten minutes or so
it will be back.
These hilltop CEneis are all males. Females I very seldom find, and
always in localities at some distance from where the mal es like to disport
themselves. Having considered all this evidence, I have arrived at the
conclusion that this hilltopping business is simply a means by which th e
males and females are brought together. The problem of finding mates
1962
Journal of the Lepidopterists' Society
65
that are other than siblings, must trouble most insects, and it must be
admitted that not all solve the difficulty by hilltopping. Among butterflies some, notably the Lycrenidre, would not meet with the problem, because they tend to form colonies, which remain in one small area, where
the necessary host plant is plentiful.
In spite of these objections, it seems certain that, in the case of species
that wander a great deal, some instinct that would draw all newly
emerged individuals towards a central point would serve them in good
stead. Suppose that every (Eneis, on emerging, is possessed of an urge
to fly uphill. The males, which are always on the wing before the females,
will become concentrated at certain high spots. The females will then
begin to arrive at these meeting places. It is a known fact that the behaviour pattern of a female insect may change after mating. We can
suppose then that since the female (Eneis, on reaching a hilltop, will
immediately meet a male, she will shortly lose her uphill instinct, which
will be replaced by an urge to search for a suitable place for oviposition.
The strongest support for this part of my theory lies in the fact that, if
females did not fly up to the hilltops, the males which persisted in staying
there would get no mates. That being so, natural selection would inevitably eradicate the habit. The short stay necessary for the females to complete business and move on would mean that a collector could easily miss
seeing them , if he were in the habit of stopping only long enough to
collect any males in residence at the time.
An interesting aspect of the problem, for which J have no good explanation, is the way in which males can establish and hold a territory.
On most peaks, only one is present at a given time, unless there is quite
a plateau, in which case several will remain about 50 yards apart. At that
distance they apparently cannot see one another. The tree clumps on my
ridge, by screening the butterflies from sight of one another, allow three
males to occupy quite a small area. When a male comes into a rival's
territory, the two flutter around each other for a time, then one, which
I cannot say of course is always the trespasser, will clear off out of sight.
Why it should do so it is difficult to say, since the other male obviously
cannot hurt it. But the utility of the system is evident. Each male is under
the necessity of investigating every butterfly which comes into its range
of vision, in case it should prove to be a female of his species. Two males
remaining continuously in sight of one another, would create an intolerable situation.
It seems probable that some species that are not hilltoppers use the
rendezvous system, although with these the means by which the meeting
place is selected remains a mystery. I know of spots near my home where,
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Vo1.l6: no.l
year after year during the correct season, I can go each day to collect
the current male Limerzitis lorquirzi Bdv., which will be replaced each
time just as are the CErzeis males on the ridge. But these Limerzitis spots
have, so far as I can make out, absolutely nothing to set them apart from
the rest of the scenery. They are not at the tops of hills, but often on a
slope.
While on the subject of hilltoppers, I would like to add some further
information that has come to light, regarding our other inveterate hilltopper, Papilio zelicaorz Luc. In this journal (Vol.7: 43-44; 1953) I stated
that on Mt. Arrowsmith there were no suitable host plants for P. zelicaorz,
and that to reach the summit from the nearest stand of umbelliferous
plants, they would have to fly about five miles over, or through, dense
forest. In 1960, while on my annual collecting trip to Mt. Arrowsmith,
I noticed a butterfly of this species, behaving in a suspicous manner.
So certain was I that it was engaged in oviposition, that after an unsuccessful attempt to collect it, I returned to examine what had appeared
to be a patch of rocks supporting a few lichens and mosses. Close examination revealed a number of tiny plants, just coming into bud. So
small were they, and so closely appressed to the rock, that anyone of
them could have been hidden by a silver dollar, yet in the aggregate
there were enough to feed several P. zelicaon larvie. I took home a
sample, and in water the buds opened into tiny yellow umbels. They
were undoubtedly a species of Lomatium, very probably L. martindalei
C. & R. I could find no ova on any of the plants, but it is, after all, immaterial whether the butterfly was ovipositing or not. By looking as if it
were laying eggs, it had led me to discover on Mt. Arrowsmith an umbelliferous plant which I had not noticed before, and which certainly
could account for the presence of P. zeMcaorz in the vicinity.
R. R. I, Wellington, B.
c., CANADA
The artist who prepared the figure for the front cover for Volume 16
is again WILLIAM VARS, of Yale University.