Dirty Hands Diaries – July 16, 2023

Silent Partners

The other day when I walked into the hoop house – that alien-looking structure in the middle of the orchard where we grow phenomenal cucumbers, tomatoes, eggplants – I saw a little green Martian… I’m kidding, this is not a story about an alien landing! As I walked into the hoop house then, a fly zoomed in through the other door and landed on a sunlit cucumber leaf. The fly was startlingly large, its stout, shiny black abdomen bristling with sparse black hairs, its fuzzy feet a bright orange to match the orange markings under its wings. Not so long ago I would have instinctively stepped back, in fear of getting bitten. But I know better now so I smiled and took a photo of one of the hard-working silent partners in our garden.

Tachinid flies, or bristle flies, can look fierce, and indeed they are, if you are a cutworm, a Colorado potato beetle, tomato worm (horn worm), cabbage worm, cabbage looper, harlequin bug, lygus bug, squash bug or cucumber beetle just to name a few of the insects that help themselves to the plants we grow with so much effort and pride. Tachinid flies, most of which are highly specialized by the way, so the more species visit the garden the better, lay their eggs directly on these individuals.

When those eggs hatch a few days later, each tiny fly larva burrows into the host and yes, you guessed it, starts feeding on it. It is a clever set-up in that the unfortunate host insect continues to live with the larvae growing inside – I’ll spare you the details. In some instances, the host will die only when the larvae reach maturity, but its death is always the end product which is exactly what we gardeners want. Sometimes the flies lay their eggs on the leaves their potential hosts devour.

But rest assured, a tachinid fly will not bite or lay eggs on you! Just like bees and bumblebees, it prefers to feed on flower nectar, so the more flowers and flowering herbs in the garden, the more tachinids. I’m sometimes lucky enough to surprise a tachinid fly in one of our flower beds. Aphid honeydew is another delicacy they are attracted to so a few aphids is not a bad thing either.

Our garden teems with silent partners. Next time I’ll write about another one I love to watch for, the beautiful Hover Fly. I promise you’ll really like this one!

Anna Mioduchowska
Green & Gold Community Garden Volunteer

To all our devoted volunteers and customers. We have started a blog called the Dirty Hands Diaries for your reading pleasure. The purpose of the blog is to share your reflections of the garden throughout the growing season. Anyone can submit an entry by sending it to us at: gggarden@ualberta.ca.