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Archive for the ‘Native Plants’ Category

A few days ago, I spotted a large (about 2 inches, or 5 cm, long), wasp-like insect nectaring on swamp milkweed (Asclepias incarnata) in my garden. Although it looked like a wasp, I suspected that it wasn’t because it appeared to have only one pair of wings and it didn’t have a narrow, wasp-like waist.

Mydas tibialis golden legged mydas fly midas on Asclepias incarnata swamp milkweed

Mystery Insect

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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 Papilio troilus on Cardinal Flower Lobelia cardinalis

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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Lobelia cardinalis Cardinal Flower inflorescense

Cardinal Flower spike

In mid to late summer, the brilliant red blooms of the Cardinal Flower (Lobelia cardinalis) brighten areas with moist to wet soils in eastern North America as well as farther west to the southwestern states and California. The Cardinal Flower is an ideal example of a plant that has flowers adapted for a single type of pollinator, the hummingbird. The only hummingbird species in northeastern North America is the Ruby-throated Hummingbird (Archilochus colubris). This hummingbird gets its name from the iridescent red patch on the throat of the males—females lack the red patch. I’ve enjoyed watching these tiny, energetic birds darting about in a patch of Cardinal Flowers in my backyard, sipping nectar while performing valuable pollination services.

The show starts in mid summer

Cardinal Flowers extend their spike-like inflorescences upward beginning in mid summer and ultimately reach a height of 24” to 48” (60 to 122 cm). Individual flowers open in succession from the bottom of the stem to the top over a period of about six weeks. Each spike can have several to over 50 individual flowers. Each flower consists of a tube about 1 1/2” (3.8 cm) long that flares out into five petals—two outstretched petals forming an upper lip and three downward pointing petals forming a lower lip.

Cardinal Flower Lobelia cardinalis male phase

Cardinal Flower male phase

Lobelia cardinalis male phase beard

Close-up of male phase “beard”

Projecting upward from between the two upper petals of the tubular flower is another tubular structure that contains both the male and female reproductive parts. When the flowers first open, they’re in the male phase. In this phase, pollen is held in the tip of the tubular reproductive structure. A tuft of white hairs, looking like a tiny beard, extends beyond the tip. When the tuft of hairs is pushed back, the tip of the tube opens and releases pollen.

Lobelia cardinalis Cardinal Flower female phase

Cardinal Flower female phase

After about five days, the flower shifts to the female phase. In this phase, the female structure called a style elongates and extends out beyond the end of the tube. On the tip of the style are the stigmas, which are receptive to pollen from male phase flowers. At any given time, a spike can have unopened flowers, male phase flowers, female phase flowers, and remnants of flowers that have finished blooming.

Cardinal Flower Lobelia cardinalis male and female phase

Male and female phase flowers in bloom on same spike

Hummingbirds at your service

Hummingbirds are attracted to red flowers, and the Cardinal Flower certainly meets this requirement. Hummingbirds also have long, grooved, forked tongues that can lick nectar from the bases of long, tubular flowers like Cardinal Flowers. The hummingbird feeds while hovering at the flower’s opening, beating its wings at about 55 times per second.

Ruby-Throated Hummingbird Archilochus colubris w Cardinal Flower Lobelia cardinalis

Bright red flowers attract female Ruby-Throated Hummingbird

As the hummingbird hovers at the Cardinal Flower’s opening and enjoys a drink of sweet nectar, the top of its head comes in contact with the flower’s reproductive parts. If the flower is in the male phase, the hummingbird’s head will brush against the tuft of hairs at the end of the reproductive tube and receive a dusting of pollen.

Ruby-Throated Hummingbird Archilochus colubris w Lobelia cardinalis male phase

Hummingbird’s head is dusted with pollen from male phase flower
Copyright Edna Greig

If the flower is in the female phase, pollen already on the hummingbird’s head will stick to the female stigmas. Since male and female phase flowers are present at the same time, the hummingbird usually is successful in transferring pollen to female phase flowers. Cardinal Flower is self-compatible, so seeds will be produced whether the pollen is transferred to a female phase flower on the same plant or on a different plant.

Ruby-Throated Hummingbird Archilochus colubris w Lobelia cardinalis female phase

Female phase stigmas pick up pollen

But … beware an interloper

This mutually beneficial relationship between Cardinal Flowers and hummingbirds can be disrupted by an interloper. Learn more in the next Eye on Nature blog post.

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Milkweed (members of the genus Asclepias) flowers are unique and fascinating structures that attract a myriad of insect pollinators. The insects are rewarded with sweet nectar that milkweed flowers produce in copious amounts. Yet, insects sometimes cannot pull free from the nectar trough and perish in the grips of the milkweed flower.

Asclepias tuberosa butterfly weed w spicebush swallowtail

Butterfly weed, true to its name, with a spicebush swallowtail butterfly

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