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Befriending the harvester

By Ranger Steve

Meeting a harvester on daily walks allows my friendship to strengthen with it. He works daily along my travel route and sometimes meets other harvesters. His encounter with them is not always agreeable. His focus is on meeting the girl of his dreams. If another harvester arrived, he’d determine if it was a rival or a potential mate.

My friend aggressively flies from his perch on a gray dogwood leaf to drive another male from his territory. The two males tumble through the air in sunlight and shade until one leaves. The established territory gives the advantage to the resident male. The traveling male departs to a nearby forest opening.

If the visitor is a female, the two also tumble around each other and disappear to a secluded area to mate. I witnessed a mated pair once this summer but only after they had already joined in copula. 

The two butterflies look similar but the female has an abdomen swollen with eggs. The two join abdomen ends and face opposite directions on a leaf. One can observe the male pumping his abdomen to deliver a spermatophore packet to the female. The packet contains both sperm and protein nutrients for her eggs.

The spermatophore is about 10 percent of the male’s weight and is energetically expensive for him to produce. Female butterfly species can determine the quality of male spermatophores by various means and that determines mating receptivity. How female harvesters determine male sperm packet quality is still unknown.

The spermatophore has a hard-outer covering that encloses sperm and proteins. Once delivered to the female, sperm exit and enter a storage pouch. Harvester eggs are laid individually among a colony of wooly aphids the butterfly finds on various plant species. The egg hatches and begins feeding on the aphids. The wooly aphids cover their bodies with a waxy covering that the caterpillar also uses to cover and conceal its body.

Ants protect the aphids that secrete a sugar solution food supply. They do not notice the caterpillar predator eating their food source. The Harvester quickly matures among the aphids. Unlike most butterflies that have five larval caterpillar stages called instars, the Harvester has four. Its “meaty” diet allows it to mature to the pupa stage quickly. 

After the sperms leave, the remaining proteins in the spermatophore are absorbed by the female and help her produce healthy robust nutrient filled eggs. As each egg passes through the reproductive tract for laying among aphids, a sperm fertilizes the egg by entering through a tiny opening in the eggshell called the micropyle. Adequate sperm is stored in the sperm pocket to fertilize the many eggs the female produces. 

On my daily walks through an area I call “Woodcock Circle,” I look for harvesters. Usually I see one but sometimes three. One day I saw three and proceeded to a trail called Julianne’s Wildflower Trail where I saw two more harvesters. How many harvesters live in the neighborhood is not known. I sometimes see a harvester along the forest edge in corners of the big field. Rich wild habitat is maintained for the harvesters.

This species is generally considered uncommon but is probably more common than we expect. Their nature niche is tied to various plant species that are fed on by wooly aphids that in turn are protected by ants. Hidden among the mass of aphids there is likely a Harvester caterpillar eating its fill. This butterfly species is the only predatory butterfly in the United States. All other butterfly caterpillars feed on plants.

It has an interesting and unique life cycle. For me, I enjoy the daily friendship encounter that is one sided. Though I like to think we are friends, it considers me an unknown passerby as it goes about its business. To support its preferred lifestyle and habitat, I maintain the forest clearing called “Woodcock Circle” where it resides. It might not know it, but we are friends because I maintain habitat for it.

Natural history questions or topic suggestions can be directed to Ranger Steve (Mueller) at odybrook@chartermi.net – Ody Brook Nature Sanctuary, 13010 Northland Dr. Cedar Springs, MI 49319 or call 616-696-1753.

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