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Archive for August, 2013

Saddleback caterpillar on corn.

Saddleback caterpillars on the underside of the corn leaf. Notice damage to the foliage.

Saddleback caterpillars on the
underside of the corn leaf.
Notice damage to the foliage.

A few weeks ago I was in the “Three Sisters Garden” picking the delicious rattlesnake beans that were climbing up the corn plants when all of a sudden I felt a very painful stinging sensation on my forearm. I couldn’t figure out what had happened. I thought at first that I had gotten scratched by the edge of a corn leaf but the stinging was very intense and I knew something else had gotten me. I looked around on the corn plant where I had been picking and saw a cluster of crazy colored caterpillars on the underside of a corn leaf. As soon as I saw the spiky hairs on those caterpillars, I knew they were the culprits. Boy, did it sting! I snapped this picture of them with my phone so I would be able to identify them later. Sorry for the poor photo. This past Saturday Eric bumped into another one as he was picking more corn – he promptly put gloves on! I was glad I was able to get some better pics!

It turns out that these very colorful caterpillars were saddleback caterpillars, the larval stage of a moth (Acharia stimulea) which is commonly found in the eastern half of the United States.

Sharp spines containing a potent hemolytic venom cover the four fleshy horns

Sharp spines containing a potent hemolytic
venom cover the four fleshy horns

The saddleback caterpillar is aptly named for the large brown spot that resembles a saddle in the middle of its bright green abdomen. At both the front and back of the abdomen are a pair of prominent fleshy “horns” that are covered with sharp spines called urticating bristles. These bristles are hollow and contain a toxin that causes a painful sting when you inadvertently rub up against the caterpillar. They are very similar to the hairs that are found on stinging nettles and cause the same type of irritating sting but in my experience the sting of this caterpillar is many times worse!

The bright coloration of these caterpillars is a warning sign to stay away! Too bad I didn’t see them before I bumped into them!

They really are quite pretty but stay away!

They really are quite pretty but stay away! This week I got better photos.

My arm turned quite red and swelled up in the area of the stings and the stinging went on for hours. It was quite impressive! Now almost 2 weeks later, it still itches a bit and I can still see the red bumps where the spines must have imbedded.

As I researched this particular “stinging” caterpillar, I discovered that, because of its rather large urticating spines and relatively potent venom, the saddleback caterpillar is considered one of the most dangerous of the stinging caterpillars; perhaps second only to the puss caterpillar. Yikes – I guess I was lucky that I just got painful rash!

It turns out that though these caterpillars are found most commonly on various trees and shrubs, they also enjoy eating the leaves of corn! I could see the damage their feeding had caused on the corn foliage. There were tan streaks on the leaves where the caterpillars had scraped the green tissue between the leaf veins.

Colorful Milkweed Tussock Moth caterpillar on swamp milkweed.

Colorful Milkweed Tussock Moth
caterpillar on swamp milkweed

This week we had an inquiry about another colorful caterpillar, the milkweed tussock moth caterpillar. These hairy orange and black caterpillars are often found at this time of the year on their favorite host plants, the milkweed. I don’t think these caterpillars sting but I for one am not going to risk picking one up to find out!

Milkweeds are also the host plant for the caterpillars of the beautiful monarch butterflies. I have just recently started seeing monarchs flitting around the Buddleia and Helianthus flowers at the nursery. The black swallowtails and yellow tiger swallowtails have been around for a while but I’m always happy to see the monarchs which usually arrive a bit later in the season. These large butterflies are so majestic and fun to watch!

Monarch butterfly visits a white Buddleia

A monarch butterfly visits Buddleia ‘White Profusion’

A beautiful Tiger Swallowtail shares the flower with a bumblebee!

A beautiful Tiger Swallowtail shares the flower with a bumblebee!

Meanwhile, beware of the spiny caterpillars!

Until next time – Happy Gardening!

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Grass blade loses water through guttation

The other morning as we sat at the breakfast table at my mom’s, we noticed that the leaves of her two pothos plants had water droplets at the tips of most of the leaves. The plants were sitting on the windowsill in the bay window. Mom noticed it first and remarked about it.

It reminded me of a question that was e-mailed to me a few years ago inquiring about this very same phenomenon.

I have recently bought a wonderful plant called weeping Aglaonema and have noticed that it’s producing water droplets at the tips of the leaves. I do not mist it and always water at the base of the plant. There are no sprinklers or water sources anywhere close to it. I know that these plants are supposed to be super good for cleaning the air and I was curious if this was a property of that.

Guttation causes a droplet of water to form at the tip of a pothos leaf

Guttation causes a drop of water to form
at the tip of a pothos leaf

This is actually the result of a rather interesting event that occurs in some plant species. The appearance of water droplets at the tips and edges of the leaves of a plant is caused by a secretory process called guttation. It often occurs under conditions of moist soil, high humidity, and relatively cool air and it usually occurs in the early morning. The morning we noticed it on Mom’s pothos happened to be a relatively cool morning but rather humid as there was a light rain falling.

Here’s what happens.

There are tiny pores called stomata on the surface of a leaf. In most plant species, these pores are predominately found on the lower leaf surface. The stomata are important for the movement of gasses (carbon dioxide and oxygen) and water vapor into and out of the leaf and they are open or closed depending upon the environmental conditions. When the stomata are open, usually during the day when it is light out and photosynthesis is occurring, water leaves the plant as water vapor through the stomatal pores. This process of water loss through the leaves is called transpiration.

Water droplets forced from hydathodes on a blade of grass.

Water droplets forced from hydathodes
on a blade of grass.

The stomata are typically closed when it’s dark, so transpiration is all but stopped at night. Since the roots continue to take up water during the night, pressure (called root pressure) builds up in the leaves and forces water out of special structures called hydathodes which are found along the leaf margins. This is called guttation and is what produces the water droplets that you sometimes see along the margins of leaves in the early morning.

The process of guttation is more common in some plant species such as strawberries, lady’s mantle, and many other perennials and annuals including pothos and Aglaonema apparently. It is frequently seen on grass in the morning and is often confused with morning dew.

So that’s your botany lesson for the day!

Until next time – Happy Gardening!

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