Tomato Hornworms Glowing in the Dark

hornworm under blacklight

hornworm under blacklight

I learned from another Master Gardener Volunteer that tomato and tobacco hornworms actually glow in the dark under blacklight. ¬†Armed with this knowledge and a cheap blacklight from Amazon, I took a little trip out to the veggie garden this evening for a most gruesome task… dispatching the hornworms munching on my tomatoes!

I walk the garden every day, whether I’m picking produce or not. This year is very hot and dry, so I spend a lot of those days hand watering plants. It takes about an hour to cover the whole garden, and I enjoy this time with nature.

The time in the garden has another benefit. I don’t use sprays in the garden, so the only way to stay on top of a problem is to catch it early. I spend a lot of those hours looking for problems.

Every morning I inspect all 24 tomato plants for green monsters chewing away at the plants. Tomatoe hornworms are voracious eaters! I mostly get tobacco hornworms, which look very similar and have the same diet.  They waddle to the end of a tomato branch or leaf, and then systematically work their way back to the base. You can see in this daytime picture the stub left behind after a tomato leaf has met its end at the mouth of a hornworm.

When I’m lucky, I find them small before they do much damage. Unfortunately, that doesn’t always happen. If they are still healthy and green and munching away, I have to do away with them. If the bluebirds are keeping an eye on me, I’ll toss the caterpillar out into an open area for them to enjoy. It’s the circle of life, and I don’t feel quite as guilty as I do when I have to do the deed. If braconid wasp cocoons are visible, I move the hornworms to a small patch of plants I keep in pots just so they can continue the parasitic cycle.

hornworm under blacklight

hornworm under blacklight

The blacklight helped find two hornworms tonight! I’ll head out each night to see if it helps cut down on time spent during the heat of the day searching. Let me know if you have any luck with hornworms or any hornworm deterrents. I’ve tried borage with no success.

hornworm on tomato

hornworm on tomato


*** This site is comprised solely of the opinions of its author, Stacey Morgan Smith. She works to promote gardening and tourism in the Shenandoah Valley of Virginia, from Roanoke to the Potomac River.***

2 comments to Tomato Hornworms Glowing in the Dark

  • Athanasia

    That’s amazing and disgusting at the same time.
    I have not seen those worms around here. The bugs most likely to attack my garden are the vine borers. We always get plenty of rain so seldom have to water. But we are getting too much this year. Enough is enough. Though it replenishes the groundwater so I don’t really want to complain.

    • Haha, I agree — they are! We have been lucky with the borers.

      It’s funny how we all have different problems — we are dry as a bone here because the mountains often break up the weather. 10 minutes north or south has a deluge and we get nothing. Ugh. I hope some of your water moves this way and you can dry out! Thanks for stopping by.

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