Nectar Thieves

In my previous post, I wrote that the mutually beneficial relationship between Cardinal Flowers and their pollinating hummingbirds could be disrupted by an interloper.

The interloper in this case is the Spicebush Swallowtail butterfly (Papilio troilus). The Spicebush Swallowtail is considered a nectar thief, a term used by ecologists to describe an insect that enters a flower to obtain nectar but that doesn’t pollinate it because the insect is physically incompatible with the flower. When the Spicebush Swallowtail sips nectar from a Cardinal Flower, its body usually doesn’t contact the flower’s reproductive parts sufficiently to pick up or deposit pollen.

Spicebush Swallowtail – a nectar thief of Cardinal Flower

Spicebush Swallowtails, sometimes two or three at a time, often descend upon my backyard Cardinal Flower patch to feed on nectar. If a hummingbird notices, it usually chases the swallowtails away, but the swallowtails quickly return.

The Spicebush Swallowtail is the only species of butterfly that I’ve seen feeding on Cardinal Flowers. I wondered why, since other butterfly species, like the Tiger Swallowtail (Papilio glaucus) and Great Spangled Fritillary (Speyeria cybele), often visit my backyard. I learned that the Spicebush Swallowtail has the longest proboscis (over 9/10”, or 2.31 cm) of all the butterflies in my area and may be the only species that can reach the nectar at the base of the Cardinal Flower. The closely-related Tiger Swallowtail has a proboscis that’s about 2/3” (1.17 cm) long, while the Great Spangled Fritillary’s proboscis is just under 6/10” (1.45 cm) long. Neither of these two species has shown an interest in the Cardinal Flowers.

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