Wednesday, March 6, 2013

Host Plants and Butterflies

The featured speaker at the recent Wildflower Association of Michigan annual conference was Dr. Douglas Tallamy of the University of Delaware.  Dr. Tallamy is the author of the book Bringing Nature Home: How You Can Sustain Wildlife with Native PlantsThe focus of Dr. Tallamy's talk at the WAM conference (and the topic of his book) is the relationship between plants, insects, and vertebrates (particularly birds).  To sum up Dr. Tallamy's ideas in two sentences:  If you want more birds in your yard, you need more insects.  To get more insects, you need to plant native plants.

Many species of herbivorous insects evolved to eat a specific type of plant.  The larva of many species of butterflies and moths can eat only a single genus or species of plant.  These plants are referred to as host plants.  If you want to have these species of butterflies around you need to allow their host plants to grow.

Butterflies and Host Plants

Monarchs and Milkweeds

Probably the best known example of butterfly and host plant relationship is that between the Monarch Butterfly (Danaus plexippus) and plants in the Milkweed family.  In Mid-Michigan the two most common milkweeds are the Common Milkweed (Asclepias syriaca) and Swamp Milkweed (Asclepias incarnata).  The caterpillar of the Monarch has coevolved with plants of the Milkweed family and cannot feed on any other species.  Unfortunately, many people view the Common Milkweed as a weed.  Even if they allow it to flower for a short time, many people will cut the plant off when it starts to seed in August.  This is exactly when Monarchs are laying eggs for the generation of butterflies that will migrate to Mexico for the winter.  If you have milkweeds and want to trim them back, do it in July so fresh growth is available for the caterpillars in August and September.

Monarch Butterfly

Monarch Caterpillar on Common Milkweed

Common Milkweed

Swamp Milkweed
Great Spangled Fritillary and Violets

Another species that relies on a single genus of plants is the Great Spangled Fritillary (Speyeria cybele).  The caterpillars of this species feed only on violets.

Great Spangled Fritillary adult feeding on Swamp Milkweed nectar

Some of the violets that grow in Mid-Michigan include:

Common Blue Violet (Viola sororia)

Dog Violet (Viola conspersa)

Downy Yellow Violet (Viola pubescens)

Long-spurred Violet (Viola rostrata)
Stinging Nettle and Butterflies

Most people do not want Stinging Nettle (Urtica dioica) plants in their yards.  Stinging nettles are covered with large numbers of hollow needle-like hairs that inject chemical into whatever brushes against them.  These chemicals cause a painful stinging sensation.  I can speak from experience that you do not want to walk through a patch of Stinging Nettles while wearing shorts.  Despite this, nettles are a very valuable host plant for many butterfly species including the Red Admiral (Vanessa atalanta), Painted Lady (Vanessa cardui), and Question Mark (Polygonia interrogationis).  All of these species also use other plants as larval hosts.

Stinging Nettle

Red Admiral

Painted Lady

Question Mark
Silver Spotted Skipper and the Pea Family (Fabaceae)

The caterpillar of the Silver-spotted Skipper (Epargyreus clarus) feeds on a variety of plants in Pea (Fabaceae) family.  These host plants include Hog Peanut (Amphicarpaea bracteata) and Showy Tick-trefoil (Desmodium canadense).

Silver-spotted Skipper

Hog Peanut

Showy Tick-trefoil
Generalists

Some species of butterflies are not tied down to a specific host plant, and instead have caterpillars that can eat a wide variety of plants.  These caterpillars can be referred to as generalists instead of specialists.  Two of the species that fit in this category are the Eastern Tiger Swallowtail (Papilio glaucus) and the Viceroy (Limenitis archippus).  Some of their shared potential larval hosts include willows, cottonwoods, birches, and cherries.  The Tiger Swallowtail can also use maple, elm, and ash trees as hosts.

Eastern Tiger Swallowtail

Viceroy

These first four plants are common larval hosts of both the Eastern Tiger Swallowtail and the Viceroy.

Black Cherry (Prunus serotina)

Eastern Cottonwood (Populus deltoides)
 
Black Willow (Salix nigra)

Paper Birch (Betula papyrifera)
 
The next five trees are hosts of the Eastern Tiger Swallowtail, but not of the Viceroy.

Silver Maple (Acer saccharinum)

Sugar Maple (Acer saccharum)

Red Maple (Acer rubrum)
 
Black Ash (Fraxinus nigra)

Green Ash (Fraxinus pennsylvanica)

These are just a few of the butterflies that rely on native plants as a host.  Very few species are able to utilize non-native trees and landscape plants as hosts for their larva.  If you want to learn more about planting native plants to help insects and birds check out the Pollinator Partnership, the Xerces Society, Wild Ones, or Bringing Nature Home. If you want to attract butterflies and other pollinators to your yard, plant native plants that they can use throughout their life cycle and not just for nectar.

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