Spending more than 100 nights per year away from home actually led McDonald to another, less expected (and slightly gross) discovery: a method of determining the predatory activity of his beetles.
After a long day with the Laricobius, McDonald worried about a different kind of bug crawling between his hotel sheets. “Bedbugs feed on blood,” he explains, “and blood fluoresces under the right wavelength light.”
So, in search of hotel bedbugs, he roamed through Seattle until he found and purchased a pocket ultraviolet wand. And although bedbug blood wasn’t what McDonald found during his investigation, he packed up the UV pen in his duffle and, several days later, brought it home to Western North Carolina.
“One night, I’m bored, I’m sick with a cold, I had this spy pen,” he says, “and I knew I also had adelgids with the predator on a tree out in the woods.”
He walked outside, shining his wand, and, suddenly, found himself standing before a thousand tiny lights.
“It looked like a Christmas tree,” he says. “Blue, yellow and chartreuse green” — with dots of brilliant orange glowing under the blacklight.
You see, he continues, the Laricobius “is like a beneficial vampire. It eats six to eight of these adelgids a day. But, no, they don’t chew them up. They’re blood feeders; they come up to the adelgid, slit it open and suck it dry.”
And because the adelgid has quinones in its blood, he says, the blood fluoresces bright under UV light. When [the Lariocbius] feeds on hemlock wooly adelgid, it leaves behind a mess, just like a vampire would — a blood spatter of blue and yellow and green.”
According to McDonald’s report, published in late 2013, an undisturbed adelgid egg sac fluoresces a bluish-white. A bleeding adult adelgid, likely attacked by Laricobius, glows a yellow-green. Predator-damaged eggs glow bright yellow. And when the Laricobius feed on their luminous prey, the blood changes color in their stomachs, leaving behind tiny dots of vivid, brilliant orange — fading to a pinkish red over time.
This information makes it easier to determine if the seasonal predator has come out to feed, whether a predator is present on a specific tree, and how much activity and how recent the tree has seen a battle between beetles and bugs.
To see more from McDonald and his colleague’s report, click here.