A Beneficial Insect

Brachonid wasp coccoons on a tomato hornworm

Brachonid wasp cocoons on a tomato hornworm

Here’s another interesting post from our friend, HerbDoc:

One of my first memories of vegetable gardening at my grandparents’ home involved being given a half pound Chock Full O’Nuts can with which to pick the ugly green tomato hornworm.  These were often fed to the chickens once picked.

Over the years I followed the routine of picking and discarding these pests when I found them, but lately have become very interested in beneficial predators.  Enter the tiny brachonid wasp.  This small insect is very dark, sometimes with tinges of red and has transparent wings.  The females have a very long ovipositor with which to lay eggs under the skin of the tomato hornworm.  The eggs hatch and the larvae eat the hornworm from the inside out.  Once they emerge they spin tiny white cocoons that look like eggs; after a couple of weeks the adult brachonids emerge through an opening in the tip and begin the process all over again.  I carefully watched one particular hornworm as it literally turned from fat and green into a black, desiccated stick!  Using my loupe, I could make out the head and what was left of the body segments.

Note to gardeners:  if you see those nasty tomato hornworms with what looks like white eggs on their backs, leave them there.  They are carrying around a very significant biological control that will not only destroy them but also their descendants….and we don’t have to go through the tedious process of picking them off the tomato plants!

What's left of the hornworm - little more than a stick!

What's left of the hornworm - little more than a stick!


About dirtynailz

Writer for a daily newspaper, gardener, tree hugger, orchid-grower, photographer, animal lover, hiker, wilderness seeker. Proponent of clover in the lawn and a dog on the bed.
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6 Responses to A Beneficial Insect

  1. wiseacre says:

    Talk about having the life sucked out of ya. Kind of reminds me of my kids.


  2. Wendy says:

    This gives me nightmares every time.


  3. Joan Valade says:

    I have not seen a hornworm with eggs on it, but I must admit…I never really look…I just kill the darn things as soon as I see them. Next time I will look.


  4. HerbDoc says:

    Terrific! I think you’ll have fewer hornworms next year if you leave the cocoons to do their work. After I wrote this post, I had several more “dried up sticks” on my tomato plants. I can’t wait until next year to see what the result will be.


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