Friday, July 20, 2012

Life and Death In the Garden

Cicada Killer Wasp
I walked out to the garden on a hot afternoon earlier this week and was confronted, or rather, investigated, by a giant wasp. No, this is not a science fiction story. The wasp in question was an eastern cicada killer, Sphecius speciosus.  At over two inches in length and marked with warning coloration like other wasps and hornets, this insect generally elicits alarm when it shows up in the garden. Fear not, however, as the energetic, territorial males—such as the one that approached me—have no sting, and are aggressive only toward other male wasps in the vicinity. They investigate any movement in their field of vision, however, and have no fear of humans. I was unable to get a shot, due to the frenetic activity. The image posted is from Texas A&M's web site. Female cicada killers have the ability to sting, but are so docile they can be picked up safely. Unless roughly handled, the wasp saves her sting for her prey, any of the several species of cicada that inhabit our area. Cicadas are paralyzed by the sting, and stored in a burrow dug by the female, where they serve as food for the wasp’s developing larvae. If you have male wasps in the garden, it is almost certain that you will also find the burrows made by the females. The entrance hole is about an inch in diameter, and there is usually a lot of spoil lying at the entrance, where the soil removed by the wasp was deposited. They like to locate them under flat stones or the surface roots of trees, for added protection. If you watch the entrance for a while, you may see a female laboriously hauling in a cicada. Cicada killer wasps are beneficial insects because cicadas can damage some crops and turfgrasses. The wasps are extremely unlikely to harm a human, and so should be welcomed into the garden.
Velvet "Ant" Wasp
Another interesting wasp typically appears at about this time each summer. It is the eastern velvet ant, Dasymutilla occidentalis, which only resembles an ant superficially. So far, I have only observed the males, which are easy to distinguish because they have wings. The wingless females spend their time on the ground searching for the burrows of solitary bumblebees. When she finds one, the female enters the burrow and lays her eggs on the developing pupae of the bumblebee. In so doing, she helps to control the bee population.
Owing to their bright red and black coloration, these insects are hard to mistake for anything else. Males have no stinger, but the females carry a sting so painful it is said to hurt “bad enough to kill a cow.” This has earned the name, “cow killer ant” for the bug, although it poses no actual threat of harm to a cow. More likely, the venom evolved to discourage insectivorous mammals, like shrews and possums. As with many venomous insects, the velvet ant advertises its weaponry with bright coloration and alternating stripes. Fortunately, the female velvet ant is so dedicated in her search for prey that she poses no threat to humans. Simply avoid her, and you won’t have anything to worry about.
A garden with many plant species and numerous micro-habitats within it will support many varieties of insects. Most will be either neutral or beneficial, as far as your food crops are concerned, and their presence will help to deter serious pests, like squash bugs. Finding a diversity of insects in the garden is a sign that you are managing your homestead wisely.

Learn more about cicada killers here. Learn more about velvet ants here.

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