Fall Harvest

The light snow here in Sackville today is a not-so-subtle reminder that the butterfly season is winding down. However on warm days a few butterflies can still be had; in the past couple of weeks I have received reports of Clouded Sulphur, Cabbage White, American Copper, American Lady, Monarch, Green Comma, Mourning Cloak, Red Admiral, and Harvester.

The Harvester report was of most interest to me, as the report was of larvae, not a chance encounter with an adult. Harvesters are unique among Maritime butterflies in that their larvae are carnivorous, feeding on Woolly Alder Aphid, a common species found in dense colonies on alder branches.  Chris Adam and Reggie Webster collected two Woolly Alder Aphid colonies near Fredericton on September 28, and after close examination indoors they found one contained a Harvester caterpillar.

Harvester caterpillar. Photograph by Chris Adam

Harvester caterpillars can be hard to detect in the aphid colonies as they are hidden in the wax jungle produced by the aphids. However, as I’ve just learned from Chris and Reggie, if you look for webbing and frass (aka caterpillar poop) produced by the harvester caterpillar you can narrow your searches.

Evidence of Harvester - note the dead aphids hanging from webbing. Photograph by Chris Adam

Another thing to keep your eyes out for when examining Woolly Alder Aphid colonies are Harvester chrysalises, which are often described as looking like monkey faces, and flower fly (Syrphidae) larvae, which also feed on the aphids. Chris has tried to rear the Harvester caterpillar he found. Since bringing the aphid colony indoors the caterpillar has grown significantly, however Chris is finding the aphid colony is dying off . Anyone reading this who is going to try to rear a Harvester might want to know the whereabouts of an extra aphid colony or two that can be brought indoors as needed.

I know I am now going to scrutinize any Woolly Alder Aphid colonies I see this fall. I am not sure how the current cold weather has affected them, but hopefully there are still some present in more sheltered spots for me to discover in the coming warm weather.


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