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| Mason wasp, Euodynerus hidalgo and caterpillar
© Beatriz Moisset. 2014
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Recently I found a wasp on a sunflower wrestling a
caterpillar almost as big as herself into submission. The caterpillar had made
considerable damage to the flower head as shown on the pictures. Finally the
hunter managed to grip its prey by the throat, if that is where caterpillars have
a throat. Carefully tucking her prey under her body, she flew away, presumably
to her nest to feed her brood with it.
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| Caterpillar held firmly behind the head
© Beatriz Moisset. 2014
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I identified the hunter as one of the mason wasps, so called
because they use clay to build nest partitions. It was a rather small wasp,
mostly black with yellow markings on its body. The wings remained folded
lengthwise. All members of the family Vespidae do this when not in flight. Now,
I finally could decipher the mystery presented to me a year earlier in the same
garden where I was doing my observations.
On that occasion, I noticed a mason wasp furiously searching
a flower head, almost a carbon copy of the one in front of my eyes. It had the
same kind of damage, but, at that point, I didn't know what or who had caused
it. The mason wasp rummaged the entire center of the blossom, even burying half
of her body in it with no apparent success. After observing these antics for a
while I moved on without finding out what she was looking for. Now, I had the
answer.
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| Another mason wasp found a year earlier
© Beatriz Moisset. 2014
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A mother mason wasp, like the one I was observing, builds
her nest inside any available hole of the right size, slightly wider than her
own body. It could be a hollow stem or some other cavity previously dug up by a
beetle or other insect. Unlike their distant cousins, hornets and
yellowjackets, they don't form large colonies. Each mother wasp minds her own
business, builds a nest where it raises maybe a dozen babies and is not
inclined to defend this small investment as ferociously as hornets tend to do.
Thus, their presence can be easily tolerated in the garden.
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Mason wasp tending her nest
© 2010 Charles Schurch Lewallen
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Interestingly the so called mason bees have similar nesting habits.
These bees are excellent pollinators of fruit trees and other plants, so gardeners
prize their services. Some gardeners provide housing for them by hanging a
bundle of hollow twigs or drilling a number of holes in a piece of wood. These
bee houses and bee hotels have been growing in popularity in recent years. You
can purchase them from several venues usually accompanied by an instructions
booklet.
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| © Beatriz Moisset. 2014 |
Mason wasps use caterpillars to feed their babies. They keep
their prey alive, so the food supply remains fresh as long as needed. They do
so by paralyzing but not killing their victims with their stingers, a delicate
operation. This is why my wasp was so busy getting the right hold of the caterpillar,
firm but not too harsh.
Most adult wasps are often seen on flowers because they feed
mostly on nectar. This particular species has another reason for visiting
flowers. This is where it finds its prey. Some caterpillars, especially some
inchworms and owlet moths, show a preference for sunflower heads. They hide in
the very heart of the flower and proceed to eat the growing seeds causing a bit
of destruction. It is nice to see that this hunting wasp prey on them
preventing further damage.
If you love pollinators you may be raising mason bees.
Perhaps you find some of the holes in your bee houses occupied by mason wasps.
You may be tempted to destroy the "invaders." Please, don't! You
probably didn't know that they help the pollinators by keeping down the
populations of plant eating insects. We need biological controls as much as we
need pollinators to maintain a healthy garden.
Additional readings
In Praise of WaspsUrban Bee Gardens. Berkeley University
Nests for Native Bees. The Xerces Society
Bee houses. National Wildlife Federation. (How to build a bee house)
Sellers of bee houses
Knox Cellars.
Mason bee homes.
List of articles
Beginners Guide to Pollinators and Other Flower Visitors
© Beatriz Moisset. 2014
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