ultimately their bases. Until the edges of the lobes come into contact,
elongated spaces between the spikes, varying from the 1/15 to the 1/10
of an inch (1.693 to 2.54 mm.) in breadth, according to the size of the
leaf, are left open. Thus an insect, if its body is not thicker than
these measurements, can easily escape between the crossed spikes, when
disturbed by the closing lobes and in- [page 312] creasing darkness;
and one of my sons actually saw a small insect thus escaping. A
moderately large insect, on the other hand, if it tries to escape
between the bars will surely be pushed back again into its horrid
prison with closing walls, for the spikes continue to cross more and
more until the edges of the lobes come into contact. A very strong
insect, however, would be able to free itself, and Mrs. Treat saw this
effected by a rose-chafer (Macrodactylus subspinosus) in the United
States. Now it would manifestly be a great disadvantage to the plant to
waste many days in remaining clasped over a minute insect, and several
additional days or weeks in afterwards recovering its sensibility;
inasmuch as a minute insect would afford but little nutriment. It would
be far better for the plant to wait for a time until a moderately large
insect was captured, and to allow all the little ones to escape; and
this advantage is secured by the slowly intercrossing marginal spikes,
which act like the large meshes of a fishing-net, allowing the small
and useless fry to escape.
As I was anxious to know whether this view was correct and as it seems
a good illustration of how cautious we ought to be in assuming, as I
had done with respect to the marginal spikes, that any fully developed
structure is useless I applied to Dr. Canby. He visited the native site
of the plant, early in the season, before the leaves had grown to their
full size, and sent me fourteen leaves, containing naturally captured
insects. Four of these had caught rather small insects, viz. three of
them ants, and the fourth a rather small fly, but the other ten had all
caught large insects, namely, five elaters, two chrysomelas, a
curculio, a thick and broad spider, and a scolopendra. Out of these ten
insects, no less than eight [page 313] were beetles,* and out of the
whole fourteen there was only one, viz. a dipterous insect, which could
readily take flight. Drosera, on the other hand, lives chiefly on
insects which are good flyers, especially Diptera, caught by the aid of
its viscid secretion. But what most concerns us is the size of the ten
larger insects. Their average length from head to tail was .256 of an
inch, the lobes of the leaves being on an average .53 of an inch in
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