The Question: It’s VERY hot and humid here in Milwaukee – the cicadas and other insects seem to be the only ones enjoying it. Last night while walking my dog about dusk, I saw two different mourning doves being “chased” by something about 1.5 inches (4 cm) or so. The bird was flying quickly – in one case it had tried to land in a maple tree and then seems to have been sent off as this shape followed it. Could the tormenter be a cicada?
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The Short Answer: Lezlie, it doesn’t seem very likely to me that it would be a cicada. I would rather expect the bird to be chasing the cicada than the other way around. But in trying to think of a 1.5 inch flying creature that a bird might wish to avoid and that might also be associated with a noisy population of cicadas, I first wondered whether it could it be a cicada killer, of which there are several species in the U.S. These large wasps (as large as 5 cm, 2 in) specialize in preying on cicadas. The female cicada killer stings a cicada to paralyze it and then stuffs the cicada down a hole dug in the ground. The cicada killer lays an egg on the cicada and when the egg hatches, the larva consumers the cicada. Female cicada killers tend to dig their holes in the same area, so in sandy, dry soil, you can sometimes see dozens or hundreds of these holes, especially when cicadas have a big year. During the summer, the males, which cannot sting, form “leks.” A lek is when males congregate to struggle for dominance and females arrive to mate – usually with the winners.
Chuck Holliday, an emeritus professor of biology at Lafayette College in Pennsylvania, has studied cicada killers extensively. He says that when they are on a lek, male cicada killers will chase anything that in any possible way could be a female cicada killer. Pretty much anything that moves.
“They will chase small birds, people and even small stones thrown in front of them. After all, for them, it’s ‘mate in the next 1-2 weeks or die childless.'”
My first thought was that maybe it was male cicada killers that chased the doves. But Professor Holliday pointed out that cicada killers in Wisconsin (which would be Sphecius speciosus) would be done mating around the middle of August. So since you made your observations in September, that pretty much rules out cicada killers. He suggested that chaser would be more likely to be European hornets (Vespa crabro), another large wasp (up to 2.4 cm for workers, 3.5 for queens). They look a bit like oversized yellow jackets. European hornets build nests in tree holes, and will sting to defend the nest. If a bird were to inadvertently fly near a European hornet nest, it will probably get chased. There have been reports of European hornets killing small birds such as hummingbirds. And Dr. Holliday suggests a hornet might even be hoping to take a bite out of a dove. “Hornets (including yellow jackets) will land on carcasses and even people and bite out a chunk of skin to take back to the grubs in their nests to feed them.”
So it seems more likely that it was a European hornet than a cicada or a cicada killer, and the connection with cicadas may be nothing more than that cicadas and European hornets are both associated with trees. But if you see it again, look to see if it’s a large hornet. If it’s a cicada killer, from a distance it will look mostly black with some red, whereas the European hornet will show yellow, like a large bee or yellow jacket.