- Author: Kathy Keatley Garvey
It's not often you see a Mexican cactus fly, Copestylum mexicanum, nectaring on a Mexican sunflower, Tithonia rotundifolia.
At first glance, you may think the insect is a carpenter bee or bumble bee.
Then you see it hovering. Then you see its head. Then you see its stubby antennae.
Fly!
It's a large black syrphid fly, aka flower fly or hover fly.
The genus Copestylum includes more than 350 species in the new world, according to Martin Hauser, senior insect biosystematist with the Plant Pest Diagnostics Branch of the California Department of Food and Agriculture (CDFA).
Lynn Kimsey, director of the Bohart Museum of Entomology and UC Davis professor of entomology, says the female Mexican cactus fly lays its eggs in rotting or dying cactus tissue.
This fly, about 3/4 of an inch long, was a few inches short of a neighboring cactus, a torch cactus, Echinopsis spachiana.
The cactus is neither dying nor rotten.
Thankfully.
The Mexican cactus fly simply stopped to sip some nectar from the Mexican sunflower.
- Author: Kathy Keatley Garvey
You've heard of "musical chairs," that anxiety-driven elimination game involving chairs, music and players. When the music stops and a chair is eliminated, the players race for the remaining seats. No one wants to be the first loser.
Well, insects, too, play "musical chairs," but with flowers as chairs. The music: the flapping or buzzing of insect wings.
Such was the case this week as two syrphid flies, aka hover flies or flower flies, kept jockeying for the same Mexican sunflower blossom (Tithonia rotundifolia).
It was a close contest between the black hover fly or Mexican cactus fly (Copestylum mexicanum) and the hover fly (probably Eristalis tenax), which is often mistaken for a honey bee. Neither wanted to be the first loser.
Who won? Neither. They abandoned the "fight" and took flight, each heading for a different blossom to forage for more nectar and pollen.
Life is like that.
- Author: Kathy Keatley Garvey
Hide the cactus! There's a Mexican cactus fly in our midst.
A large black fly hovers over a Mexican sunflower (Tithonia) in our bee garden and then drops down to sip some nectar. At first glance it looks like a carpenter bee but this one hovers like a syrphid fly, aka flower fly or hover fly.
"Hover fly," I say.
Entomologists Martin Hauser, Lynn Kimsey and Robbin Thorp quickly identified the critter.
Hauser, senior insect biosystematist with the Plant Pest Diagnostics Branch of the California Department of Food and Agriculture, says it's in the genus Copestylum (with over 350 species in the new world) and figured it to be the species, mexicanum, commonly known as the Mexican cactus fly.
Said Lynn Kimsey, director of the Bohart Museum of Entomology and professor of entomology at UC Davis: "Nice, this is actually a kind of syrphid flower fly, better known as a cactus fly. The larvae breed in rotting cactus tissue."
Native pollinator specialist Robbin Thorp, emeritus professor of entomology, also figured it to be a Mexican cactus fly, Copestylum mexicanum. "It's commonly known as a cactus fly (Syrphidae, Tribe Volucellini). "It used to be in the genus Volucella, But now it's in the genus Copestylum."
This fly is not small. It's about 3/4 of an inch long. It lays its eggs in rotting plant material "and they really like rotting cacti," Hauser commented. "As far as I know, they only go into dying cacti and do not attack healthy cacti…. But there is actually not much known about their biology."
The resident cacti expert at our house is worried, showing his best prickly pear expression. He quickly canvasses the yard. Whew! No rotting cacti. All thriving and in good health.
So far, so good...
