A Killer Among Us - Cicada Killers By: Kevin Williams, Grundy County Conservation Director
September 6, 2013
I received a call a few weeks ago from a woman looking for information. She was looking for help. That is not an uncommon occurrence to have folks calling for wildlife information. If I cannot give them an answer (that does happen occasionally) then I’ll refer them to someplace else if possible. In this case, they had exhausted the other places already. I had been the referral spot from others. She began describing these tunnels that were appearing in her yard – especially along her sidewalk but other places in the yard, too. The entrances are ? or an inch wide. The piles of dirt found out front of each were evidence that they were deep. “What are they” was the question. And this was followed closely by the second question “How do we get rid of them?” I stopped by the house and took a look at these tunnels because quite frankly I was a bit baffled from our telephone conversation about them. Even after examining them, I needed to do some searching for answers. The first thought after looking at the excavations was the insect we call cicadas. But I’ll confess, I didn’t think that cicadas emerged from the ground with quite the gusto or effort to cause what these things. It turns out that they were cicada related but made by a cicada predator and not the cicada itself. The culprits were cicada killers. At least three different species of wasps construct nests in the ground in Iowa. These “digger wasps” include the cicada killer wasp. And these are the largest wasps found in Iowa. Cicada killer wasps may be up to 2 inches long! They are black with yellow markings on the thorax and abdomen and they have rusty colored wings. The cicada killer wasp and other digger wasps are solitary wasps; that is, they live independently rather than in colonies and do not depend on other members of a colony to share in the raising of young or the maintaining of a nest. Other solitary wasps include the mud daubers and potter wasps. Solitary wasps put paralyzed insects or spiders inside the nest as food for their offspring. Female cicada killer wasps capture annual cicadas in July and August and place them in cells located at the ends of tunnels they have dug in the ground. Each tunnel is about the size of a quarter and extends 24 inches or more into the ground. One or two paralyzed cicadas are placed in each cell, and a single egg deposited before the cell is closed by the female, who flies away, never to return. The wasp grubs feed on the cicadas and develop into wasps that emerge the following summer. The cicada killer, like other solitary wasps, has the capability to sting, but won’t unless handled or threatened. Only female wasps have the ability to sting. Stings inflicted by solitary wasps are usually not severe but reaction varies with each individual. So, if female cicada killers have stingers but are not quick to use them on us, then what do they use them for instead? They plunge into cicadas to inject venom that paralyzes them. With bodies up to two inches in length, huge jaws, and glossy black paintjobs streaked with yellow, they are unmistakable, and more than a little intimidating. They emerge in July and August, to coincide with the hatching of cicadas, their sole prey. We know how they get the cicada that they need but getting it back to the burrow can be an all-day affair. It may be three times the killer’s own weight—too heavy to properly fly with. Instead she drags it up the nearest tree, then launches herself, prey in claw, and glides as far as possible toward her burrow. She may have to repeat the process half a dozen times. Back at the burrow, she deposits the paralyzed cicada in a brood chamber. Then she lays an egg and carefully tucks it beneath the cicada’s foreleg, beside the puncture wound from her sting. The female then seals the chamber with dirt, the cicada still living and immobilized within it. A few days later the egg hatches and grub begins to eat the cicada alive, using the puncture wood as an entry point. Later, the grub spins a cocoon, in which it metamorphoses into an adult wasp, emerging the following year. It truly is a wonderful creation that we share!
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