Palo Verde beetles show up; is rain far behind?

As people in the Phoenix area eagerly anticipate the first monsoon rains of the summer, there is already a sign that the wait might not last too much longer.

Palo Verde beetles are starting to show up.

The big, mostly harmless bugs usually are a welcome presence every summer. They can grow to as large as five inches long and are mistaken for giant, flying cockroaches by some.

Their sheer size can cause folks who are squeamish about such things to freak out, even though the big bugs aren’t really interested in people.

But they aren’t meteorologists. It’s just a coincidence that their appearance generally coincides with the start of the monsoon around the Phoenix area.

Why the beetles come out now

Dawn Gouge, a public health entomologist with the University of Arizona, said the most visible part of the Palo Verde beetle’s life cycle – the adult phase – starts at about the same time the monsoon finally delivers storms.

She said they spend years underground as grubs munching on the roots of Palo Verde trees.

“Palo Verde root borer, derobrachus hovorei, can feed for a few years before pupating (becoming adults) and

emerging from June-August,” Gouge said via email. “We have a number of similar species found in the Southwest, some of which do seem to emerge a little before the monsoons, but yes, the monsoon rains coincide with PVRB emergence.”

What are the beetles doing here?

In short, they come up this time of year looking for love. The adult beetles don’t eat much. They don’t make a lot of noise like cicadas. They aren’t looking to sting anybody (they can’t anyway) and while they can bite, that usually only happens if you handle them.

They have a one-track mind at this stage in their lives. Once they mate, they’re not long for this world. They crawl back into the roots of Palo Verde trees to lay their eggs and die.

Why they’re pretty much harmless

Palo Verde beetles have menacing looking jaws, and they can give you a pretty good bite if you handle one. They also have spines on their bodies which look more dangerous than they are.

But they aren’t looking for a fight, Gouge said

“They can pinch using their mouth parts, but they do not feed as adults, so they are not trying to eat you,” she said.

Their biggest threat comes from the fact that they aren’t particularly agile fliers and their sheer sizes means you’ll remember it if they crash into you.

“If you collide with one riding a bike or a motorcycle, you’ll hate them forever,” Gouge said.