These
caterpillars cannot be caught by hand, and hitherto it has proved
exceedingly difficult to cope with them. However, when they have changed
into the perfect state, the corresponding butterflies and moths, like
most other winged insects, are strongly attracted by a bright light. As
acetylene can easily be burnt in a portable apparatus, and as the burners
can be supplied with gas at such comparatively high pressure that the
flames are capable of withstanding sharp gusts of wind even when not
protected by glass, the brilliant light given by acetylene forms an
excellent method of destroying the insects before they have had time to
lay their eggs. Two methods of using the light have been tried with
astonishing success: in one a naked flame is supported within some
receptacle, such as a barrel with one end knocked out, the interior of
which is painted heavily with treacle; in the other the flame is
supported over an open dish filled with some cheap heavy oil (or perhaps
treacle would do equally well). In the first case the insects are
attracted by the light and are caught by the adhesive surfaces; in the
second they are attracted and singed, and then drowned in, or caught by,
the liquid.
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