The frontal ridges have been likened to ramps leading insects to the trap. Insects are attracted to the nectar in the collar region. Once inside the pitcher, it is difficult for the insect to escape. The collar is surmounted by the spines of the rim of the mouth which present a formidable barrier. If the insect slips, it winds up in the watery bath within the cavity of the pitcher. The walls in and above the water are smooth and offer no foothold. Should the victim manage to scale the walls after extricating himself from the digestive bath, he encounters the rim of the collar which is similar to a lobster trap in that it allows entrance but prohibits exits. The rim of the collar overhangs the walls of the pitcher virtually preventing an insect from climbing out. (Fig. 3-24) Flying insects may try to fly out through the transparent areas in the lid only to fall in the pitcher's enzyme and bacterial bath. Some believe that the transparent areas in the lid allow light to pass through and shine on the liquid below attracting insects to the pitcher's depths. Both theories are supportable.
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