Salutations, BugFans,
Time for a mid-summer brain-stretch—lots of good science vocabulary in this story.
A few weeks ago, the BugLady photographed this small insect ovipositing on an unopened daisy fleabane flower. “What a strange-looking little fly,” she thought to herself. And when she put it up on the monitor, she thought “What odd antennae for a fly!” If BugFan Gretchen hadn’t nudged her toward the Wedge-shaped beetles (family Ripiphoridae), it might have languished in the “X-Files,” unidentified, for a long time. The BugLady thinks it belongs in a group called the Ripiphorus fasciatus complex (no common name). Her only previous acquaintance with the family was a slim beetle named Macrosaigon (of previous BOTW fame), and there’s not much of a family resemblance.
Wedge-shaped Beetles
Ripiphoridae comes from a Greek word meaning fan carrier, a reference to the fancy antennae sported by the male (it really should be Rhipiphoridae, but an early transcribing error/misspelling by a taxonomist cannot be corrected at this stage of the game). There are about 50 species of these Ripiphorid beetles in North America, and 30 of them are in the genus Ripiphorus. While the general outline of how the family operates has been charted, only one species in the genus Ripiphorus has been studied, and it’s assumed that the other 29 follow the same general pattern.
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Ripiphorus beetles are smallish, chunky, “bug-eyed,” and hump-backed, with an abdomen that curves under the body and extremely short elytra—just a little scale at the base of each flying wing. With their wings exposed and held out over their backs, they are easily mistaken for flies and wasps as they visit flowers. In many species, the female’s antennae are once-divided pectinate or monoflabellate (flabellate, from the Latin flabellum, meaning fan). A Classical redundancy but each joint of the male’s fancier antennae has two branches (biflabellate).
Determination of the genus is easier than of the species (according to bugguide.net, “species identification of Ripiphorus may be extremely difficult even with specimens in hand.”), in part because in many Ripiphorid species, especially in the genus Ripiphorus, the adults are uncommonly seen and very short-lived (Ripiphorus males may live only a single day and females not much longer—when the BugLady returned the next day she could not find them). In addition, the males look sufficiently different from females so that taxonomists aren’t always sure who goes with whom. Evans, in Beetles of Eastern North America, says “Genus is in need of revision.”
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One of their claims to fame (besides their clever disguise) is that their larvae are parasitoids—parasitoids find a host and consume it slowly, from the inside or the outside, making their host last until the interloper is ready to pupate. It’s a highly unusual lifestyle for a beetle—most practitioners are flies or wasps. Their hosts are mainly the larvae of ground-nesting bees, each species of beetle targeting certain genera of bees. Hosts of Ripiphorus fasciatus include several species of digger bees and sweat bees.
Here’s how it works. Females oviposit in flowers just as the buds start to open. They may leave five to fifteen eggs in a single flower (females of R. smithii, the best-studied Ripiphorus species, produced as many as 850 eggs). The flowers open and the eggs hatch just as pollinators begin to visit, and the assertive first stage/instar beetle larvae stand erect on the flowers to intercept their ancestral hosts. These very active larvae are called triungulins or planidia—the terms are often used interchangeably (planidium comes from the Greek word for roaming). This is not your typical soft, sluggish beetle grub. Triungulins are somewhat armored, and although some have claws or sucker pads on their feet that allow them to attach to visiting bees and ride away with them to their underground nests, Ripiphorus triungulins use their mandibles to grab onto a bee (the BugLady thinks that phoresy—when one organism uses another, harmlessly, as a taxi—is amazing). You can see the reddish Ripiphorid triungulins under the bee’s abdomen.
Once there, the triungulin enters one of the bee’s egg chambers, and there it waits, until the bee has finished caching pollen and nectar inside for her offspring. She lays an egg and closes the chamber, sealing the Ripiphorid larva in, too. When the bee larva hatches, the triungulin chews its way into its host and feeds within (as an endoparasite). The two overwinter as larvae, like Matryoshka dolls, with the Ripiphorus larva still in its first instar, but it starts doing real damage the next spring as the bee prepares to pupate. It exits its host’s body and starts eating from the outside (an ectoparasite), molts five times (looking more like a typical soft, beetle grub), and finally pupates in the cell when the bee has been consumed. It emerges as an adult and exits the bee’s tunnel.
Insects that produce larvae that change form and function during their larval lives rather than simply growing larger are said to develop via hypermetamorphisis.
With the clock ticking loudly, how do Ripiphorus fasciatus males find a female? They hang around the underground nest tunnels of their host species, hoping to snag a newly emerged female as she leaves the tunnel. Scientists suspect that Ripiphorus fasciatus females use pheromones (airborne chemical “scents”) to attract males, and his fancy antennae allow him to sense those signals. Some species stage mating swarms.
Seriously—it is not a fly!
The BugLady