Angier on dragonflies

April 2, 2013 • 10:05 am

Natalie Angier has a lovely new post about dragonflies in today’s New York Times: “Nature’s drone: pretty and deadly.” As usual, it’s a felicitious combination of good writing and intriguing science, and there’s a nice video on dragonfly research to accompany it, as well as a new feature: a movie that heads the story and starts automatically. These lovely insects turn out to be the honey badgers of the insect world, mean and voracious predators. A few bits from the article:

When setting off to feed on other flying insects, dragonflies manage to snatch their targets in midair more than 95 percent of the time, often wolfishly consuming the fresh meat on the spur without bothering to alight. “They’ll tear up the prey and mash it into a glob, munch, munch, munch,” said Michael L. May, an emeritus professor of entomology at Rutgers. “It almost looks like a wad of snuff in the mouth before they swallow it.”

Next step: grab more food. Dragonflies may be bantam, but their appetite is bottomless. Stacey Combes, who studies the biomechanics of dragonfly flight at Harvard, once watched a laboratory dragonfly eat 30 flies in a row. “It would have happily kept eating,” she said, “if there had been more food available.”

. . . as a dragonfly closes in on a meal, it maintains an image of the moving prey on the same spot, the same compass point of its visual field. “The image of the prey is getting bigger, but if it’s always on the same spot of the retina, the dragonfly will intercept its target,” said Paloma T. Gonzalez-Bellido, an author of the new report who now works at the Marine Biological Laboratory in Woods Hole, Mass.

As a rule, the hunted remains clueless until it’s all over. “Before I got into this work, I’d assumed it was an active chase, like a lion going after an impala,” Dr. Combes said. “But it’s more like ambush predation. The dragonfly comes from behind and below, and the prey doesn’t know what’s coming.”

She also describes the results given in a new paper in Current Biology (I haven’t read it):  by monitoring single neurons, researchers have found that dragonflies have a form “selective attention” (paying full attention to two objects alternately) that’s usually found in species with much more complex brains. This is apparently useful in helping dragonflies select a single prey item from a moving swarm.

Here are two dragonfly videos. First, an Attenborough clip showing their four wings working in slow motion:

. . . and an 8.5-minute video on the general biology of dragonflies (order Odonata) and mantids (order Mantodea).

16 thoughts on “Angier on dragonflies

  1. I’m sure there are resources out there, perhaps even mentioned in the NYT piece that I’ve yet to read. But I’m also guessing that readers here might have interesting contributions of their own.

    Any suggestions on good ways to attract dragonflies to a garden and make them happy enough to hang around for a while?



    1. Dragonflies will find your garden if you can supply them with a small pond with no fish, preferably rather shallow, some shade and/or with floating and emergent plants.

      I have a backyard pond about 7x5x1.5ft deep (2m x 1.5 m, ca 50 cm)in a small town in the US Northwest. The pond hosts breeding populations of tree frogs, salamanders, and many interesting insects including 3 spp. of dragonflies and one species of damselfly. Fascinating to see these emerge, by the way.

      Biocontrol of mosquitoes is necessary and straightforward — Bti pellets [mosquito-specific bacteria, available in garden stores] early in the season, none later when back-swimmers sweep the larvae and water striders catch any surviving mosquitoes on emergence.

  2. I have always had a soft spot for dragonflies. One thing I had noticed is I never see them walk (!). I wonder if they actually can, or if they gave that up for their other abilities.

  3. Attenborough says the dragonfly uses “its two pairs of wings quite independently”, but that’s not what I’m seeing. To me it looks like the rear pair is consistently about 120 degrees out of phase with the forward pair. So I’d call it “coordinated but not synchronized” rather than independent”.

  4. There are other cool things about dragonflies. Their juvenile stage is aquatic, and they have some of the weirdest mouthparts in the insect realm. Their labrum (basically the lower lip) is a surprisingly long arm-like thing that is folded under their chest. They catch live prey (usually things like mosquito larvae) by stalking it, then suddenly shooting out their labrum and grasping it with the end which can fold like salad tongs. The food is then yanked back into their their mouth.
    Oh, and the juveniles can ‘swim’ with jet propulsion by shooting water out their anus.
    And male dragonflies have really weird reproductive organs.

    1. The aquatic larvae of dragonflies are also voracious indiscriminate killing machines. I have seen a dragonfly land on a leaf of an aquatic plant and start to lay eggs into the water, then be grabbed by a dragonfly nymph – possibly of a different species, though I don’t really believe the nymph would care.

    2. The “penis scoop” that male dragonflies have, to remove the previous male’s sperm before “making the beast with eight wings” is, to my mind, the single thing in nature that most loudly screams “evolution” and can’t be explained in any manner whatsoever by creationists (outside of inexplicable and unnecessary divine caprice). However, if anyone has any other candidates, I’d certainly like to hear about them! (Currently, second on my list is the broken vitamin C gene, but I’m sure there are thousands of evolutionary oddities of which I as yet know nothing).

  5. Dragonflies have always been one of my favorites. In addition to how amazing they truly are some of that favoritism may be due to my reading “Three From The Legion” by Jack Williamson when I was a boy.

  6. ” “They’ll tear up the prey and mash it into a glob, munch, munch, munch,” said Michael L. May, an emeritus professor of entomology at Rutgers.”

    I wish scientist would learn to communicate to the general public more clearly, instead of filling these pieces with specialized jargon that laypeople have trouble understanding.

    1. Interesting point – talking about scientists & laypeople makes scientists sound too much like a priesthood, which they are not.

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